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Activity of gemifloxacin tested against Neisseria gonorrhoeae isolates including antimicrobial-resistant phenotypes
Diagnostic Microbiology and Infectious Disease 54 (2006) 127 – 134 www.elsevier.com/locate/diagmicrobio
Antimicrobial susceptibility studies
Activity of gemifloxacin tested against Neisseria gonorrhoeae isolates including antimicrobial-resistant phenotypes Sudha Pottumarthya, Thomas R. Fritschea, Ronald N. Jonesa,b,T a
Jones Microbiology Institute Laboratories, North Liberty, IA 52317, USA b Tufts University School of Medicine, Boston, MA, USA Received 29 June 2005; accepted 29 August 2005
Abstract The antigonococcal potency of gemifloxacin and 5 reference comparator antimicrobials was determined for a selected collection of gonococcal isolates. The 250 Neisseria gonorrhoeae strains were inclusive of (1) 50 historic strains from Japan with elevated fluoroquinolone minimal inhibitory concentration values (QRNG) and (2) 200 contemporary strains from clinical specimens in 2004 (176 from 6 sentinel sites in the United States and 24 bacteremic isolates from the SENTRY Antimicrobial Surveillance Program). The rank order of potency of the tested antimicrobials for the entire collection was: ceftriaxone (MIC90 = 0.06 Ag/mL) N gemifloxacin (1 Ag/mL) N tetracycline (2 Ag/mL) N ciprofloxacin = levofloxacin = penicillin (4 Ag/mL). The activity of gemifloxacin was not affected by penicillinase production; however, its activity was decreased for penicillin-resistant strains. Cross-resistance between gemifloxacin and the older fluoroquinolones was present, and the gemifloxacin MIC90 value was higher for the ciprofloxacin-resistant strains compared with the ciprofloxacin-susceptible strains (2 versus 0.016 Ag/mL, respectively). More than 20.0% of the recent clinical strains were resistant to penicillin, tetracycline, and ciprofloxacin with N 30.0% of gonococci resistant to ciprofloxacin in Washington State and Hawaii. The historic QRNG strains from the Far East were predominantly of intermediate susceptibility (88.0%) to ciprofloxacin, with a gemifloxacin MIC90 value of only 0.25 Ag/mL. The bacteremic gonococcal strains were exquisitely susceptible to the 3 quinolones tested (ciprofloxacin, levofloxacin, and gemifloxacin, MIC90 at V 0.03 Ag/mL) and ceftriaxone (MIC90 = 0.06 Ag/mL). In summary, the potency of gemifloxacin was competitive and positioned between that of ceftriaxone and older quinolones or penicillin or tetracycline, irrespective of the gonococcal resistance phenotype. Gemifloxacin should be considered for further development as a therapeutic option to treat uncomplicated infections due to emerging strains resistant to penicillins, tetracycline, and some older fluoroquinolones. D 2006 Elsevier Inc. All rights reserved. Keywords: Gemifloxacin; N. gonorrhoeae; SENTRY program; Fluoroquinolones; Resistance; Ceftriaxone
1. Introduction Over 4 decades of directed research and development in the field of quinolones have led to the development of a new group of bnovelQ or brespiratoryQ fluoroquinolones (Appelbaum and Hunter, 2000; Emmerson and Jones, 2003). These new compounds developed for the 21st century, follow a better understanding of structure–activity relationships and are characterized by enhanced activity against Gram-positive cocci, especially Streptococcus pneumoniae, as well as many intracellular pathogens, while retaining
T Corresponding author. Jones Microbiology Institute Laboratories, 345 Beaver Kreek Centre, Suite A, North Liberty, IA 52317, USA. Tel.: +1319-665-3370; fax: +1-319-665-3371. E-mail address: [email protected] (R.N. Jones). 0732-8893/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2005.08.013
excellent activity against Gram-negative organisms (Emmerson and Jones, 2003; Jones, 2002). Gemifloxacin (formerly SB265805, LB20304) represents one such synthetic broad-spectrum fluoronaphthyridone with high affinity for both fluoroquinolone target enzymes (DNA gyrase and topoisomerase IV) at therapeutically achievable drug concentrations (Lowe and Lamb, 2000; Morrissey and Tillotson, 2004). This bdual-targetingQ action of gemifloxacin confers higher in vitro activity against first- and second-step fluoroquinolone-resistant mutants of pneumococci compared with the other marketed fluoroquinolones analyzed (Appelbaum et al., 2004; File and Iannini, 2003). Studies conducted in the late 1990s testing clinical strains of Neisseria gonorrhoeae, including strains with reduced susceptibility to quinolones (QRNG), established the higher potency of gemifloxacin (Berron et al., 2000; Jones et al.,
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2000a, 2000b; Tanaka et al., 2000a, 2000b). Testing 150 clinical strains of gonococci, 33.3% of which had an elevated ciprofloxacin minimal inhibitory concentration (MIC; 43 intermediate susceptibility [MIC = 0.12– 0.5 Ag/mL] and 7 resistant [MIC z 1 Ag/mL] obtained from Japan, United States, and the Netherlands), the authors found a gemifloxacin MIC90 result of 0.12 Ag/mL that was lower than those recorded for trovafloxacin (0.25 Ag/mL) and for moxifloxacin or grepafloxacin (0.5 Ag/mL) (Jones et al., 2000a). Similarly in Japan, testing 94 consecutive clinical isolates of N. gonorrhoeae from 1992 to 1993 and 100 isolates from 1996 to 1997 (including 31 ciprofloxacinresistant strains), Tanaka et al. (2000a, 2000b) substantiated the higher potency of gemifloxacin with MIC90 values of 0.03 and 0.12 Ag/mL, respectively. This was in contrast to the MIC90 values of 0.12– 0.25 Ag/mL (for 1992–1993 isolates) and from 0.5 to 2 Ag/mL (for 1996–1997 isolates) of the other fluoroquinolones analyzed (sparfloxacin, trovafloxacin, tosufloxacin, and levofloxacin) (Tanaka et al., 2000a, 2000b). However, the authors also noted that the gemifloxacin MIC90 value for the 1996–1997 isolates was 4-fold higher than that for the 1992–1993 isolates (0.12 versus 0.03 Ag/mL), and that the MIC90 values for the comparator fluoroquinolones were 2- to 8-fold greater for the 1996 –1997 isolates, reiterating the need for continued resistance surveillance among gonococci (Tanaka et al., 2000a, 2000b). To evaluate if gemifloxacin has retained its superior potency among fluoroquinolones against gonococcal isolates, which have since evolved further and developed higher levels of resistance to fluoroquinolones, we tested a collection of 250 N. gonorrhoeae isolates. The collection was chosen to represent well-characterized genotypes of QRNG, multiple phenotypes of h-lactam, tetracycline, and QRNG resistance, and a sample of recent clinical isolates (2004) of N. gonorrhoeae isolated from blood cultures and also from 6 distinct geographic locations in the United States, where QRNG has been reported to be endemic/ epidemic (Centers for Disease Control and Prevention [CDC], 2002a, 2002b, 2004a, 2004b; Wang et al., 2003).
2. Materials and methods
(36, 20.5%), Oregon (15, 8.5%), and Washington (70, 39.8%). More than one fourth of the strains from the entire collection (74, 29.6%) had well-characterized resistance phenotypes by mechanisms analysis: 50 QRNG isolates, 14 strains resistant to penicillin and tetracycline, and 10 isolates with intermediate susceptibility to penicillin. The QRNG strains were isolated in the Far East and characterized in Japan (courtesy of Professors Tanaka and Deguchi). More than half (29, 58.0%) of these QRNG strains have documented mutations in the quinoloneresistance–determining regions (QRDR) with (1) a single amino acid substitution in gyrA (19 strains), (2) single substitution in both gyrA and parC (7 strains), and (3) double amino acid substitution in gyrA and a single mutation in parC (3 strains) (Deguchi et al., 1995, 1996). 2.2. Susceptibility testing methods MICs of 6 antimicrobial agents were determined by the reference agar dilution method using GC agar base supplemented with a defined supplement (National Committee for Clinical Laboratory Standards, 2003). The antimicrobial agents tested were: gemifloxacin (Oscient Pharmaceuticals, MA), ciprofloxacin, levofloxacin, penicillin, tetracycline, and ceftriaxone. The results were interpreted according to the criteria of the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) (CLSI, 2005). The following quality control strains were used to validate the study: N. gonorrhoeae ATCC 49226 and Staphylococcus aureus ATCC 29213 (CLSI, 2005). 2.3. Data analysis The results were analyzed to determine the effect of the various resistance mechanisms, such as penicillinase production and penicillin and fluoroquinolone susceptibility category on the activity of gemifloxacin and its peer drugs. The results were also stratified to analyze the effect of geographical distribution and isolation from blood on the antimicrobial susceptibility profiles of the gonococcal isolates. The activity of the antimicrobials against the historic QRNG gonococcal isolates from the Far East (Tanaka et al., 2000a, 2000b, 2004; Deguchi et al., 1995, 1996) was analyzed separately.
2.1. Strain collection The selected collection of 250 N. gonorrhoeae clinical isolates included 176 (70.4%) recent strains isolated from clinical specimens in 2004 from geographic sites in the United States, 24 recent clinical bacteremic strains from the SENTRY Antimicrobial Surveillance Program, and 50 historic QRNG Japanese strains from the Jones Microbiology Institute (North Liberty, IA) laboratories’ collection were analyzed. The clinical strains were obtained from 6 geographically distinct sites in the United States where QRNG has been reported to be endemic/epidemic, which includes California (5 strains, 2.8% of recent clinical isolates), Hawaii (25, 14.2%), New York (25, 14.2%), Ohio
Table 1 Gemifloxacin activity compared with reference agents when tested against 250 strains of N. gonorrhoeae Antimicrobial agent Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
MIC (Ag/mL)
Susceptible/ resistant (%)a
50%
90%
Range
0.016 V 0.008 0.016 1 0.5 V 0.008
1 4 4 4 2 0.06
V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.016 to N 4 0.06 to N 4 V 0.008 to 0.12
/ 61.2/20.0 / 5.6/31.2 19.6/23.6 100.0/
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005).
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3. Results 3.1. Activity of gemifloxacin and 5 comparator antimicrobial agents against N. gonorrhoeae Gemifloxacin MIC results were compared with 5 antimicrobials commonly used as reference agents (Table 1).
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The rank order of potency of these antimicrobials for the entire collection (250 isolates) was ceftriaxone (MIC90 = 0.06 Ag/mL) N gemifloxacin (1 Ag/mL) N tetracycline (2 Ag/mL) N ciprofloxacin = levofloxacin = penicillin (4 Ag/mL). Using MIC90 for comparison, gemifloxacin was consistently 4-fold more potent than the other quinolones
Table 2 Comparative gemifloxacin activity tested against N. gonorrhoeae isolates having defined resistance mechanisms or interpretive categories for h-lactams and ciprofloxacin Organism group (no. tested)
Penicillin Susceptible (14)
Intermediate (158)
Resistant (78)
h-Lactamase–positive (28)
h-Lactamase–negative (222)
Ciprofloxacin Susceptible (153)
Intermediate (47)
Resistant (50)
Nonsusceptible (50)b
Antimicrobial agent
MIC (Ag/mL)
Susceptible/ resistant (%)a
50%
90%
Range
Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone
V 0.008 V 0.008 0.016 0.25 V 0.008 V 0.008 V 0.008 0.016 0.5 V 0.008 0.06 0.25 0.25 2 0.03 0.06 0.25 0.25 2 V 0.008 V 0.008 V 0.008 0.016 0.5 V 0.008
0.06 0.12 0.12 0.5 V 0.008 1 4 4 1 0.016 1 N4 N4 4 0.12 0.5 2 2 N4 0.03 1 4 4 2 0.06
V 0.008 to 0.06 V 0.008 to 0.12 V 0.008 to 0.25 0.06 to 0.5 V 0.008 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.12 to N 4 V 0.008 to 0.12 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.25 to N 4 V 0.008 to 0.12 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.25 to N 4 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.06 to N 4 V 0.008 to 0.12
/ 85.7/0.0 / 85.7/0.0 100.0/ / 74.1/19.0 / 22.8/7.0 100.0/ / 30.8/25.6 / 1.3/61.5 100.0/ / 32.1/25.0 / 3.6/64.3 100.0/ / 64.9/19.4 / 21.6/18.5 100.0/
Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
V 0.008 0.016 0.25 0.5 V 0.008 0.06 0.25 2 1 0.03 1 4 1 1 0.016 0.06 0.25 0.25 2 1 0.03
0.016 0.03 2 2 0.03 0.12 0.5 N4 2 0.12 2 N4 N4 4 0.03 0.25 1 1 N4 2 0.12
V 0.008 to 0.016 V 0.008 to 0.06 0.016 to N 4 0.06 to N 4 V 0.008 to 0.06 0.016 to 0.25 0.12 to 0.5 0.03 to N 4 0.5 to N 4 V 0.008 to 0.12 0.06 to 2 0.06 to N 4 0.25 to N 4 0.12 to N 4 V 0.008 to 0.06 0.03 to 1 0.12 to N 4 0.12 to 4 0.03 to N 4 0.5 to 4 V 0.008 to 0.12
/ / 7.8/15.7 31.4/14.4 100.0/ / / 4.3/72.3 0.0/31.9 100.0/ / / 0.0/40.0 2.0/44.0 100.0/ / 0.0/12.0 / 4.0/70.0 0.0/36.0 100.0/
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005). b Fifty Far East clinical isolates from 1994 to 1997 with defined QRDR changes.
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tested (1 versus 4 Ag/mL), and the highest gemifloxacin MIC recorded was only 2 Ag/mL. The QRNG rate was 38.8% and high-level penicillin and tetracycline resistance rates were elevated at 31.2% and 23.6% respectively. No isolates were resistant to the parenteral cephalosporin (ceftriaxone) tested.
3.2. Activity of gemifloxacin and 5 comparators categorized by b-lactam susceptibilities Penicillinase-producing N. gonorrhoeae (PPNG) constituted 11.2% of the collection tested (Table 2). Production of the penicillinase did not result in any adverse changes in
Table 3 Gemifloxacin and 5 comparison agents tested against recent (2004) genital and blood culture isolates listed by geographic area (United States) or specimen source Organism group (no. tested)
Antimicrobial agent
California (5)
Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
MIC (Ag/mL) 50%
Hawaii (25)
New York (25)
Ohio (36)
Oregon (15)
Washington (70)
Bacteremia (24)
All clinical cases (200)
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005).
V 0.008 V 0.008 0.016 1 0.5 V 0.008 0.5 4 2 1 1 V 0.008 0.016 V 0.008 0.016 0.25 0.5 V 0.008 V 0.008 V 0.008 0.016 0.25 0.25 V 0.008 V 0.008 V 0.008 0.016 0.25 0.5 V 0.008 V 0.008 V 0.008 0.016 0.5 0.5 V 0.008 V 0.008 0.016 0.016 1 1 0.016 V 0.008 V 0.008 0.016 0.5 0.5 V 0.008
Susceptible/ resistant (%)a 90%
Range
1 4 4 N4 N4 0.016 0.016 0.016 0.03 1 1 0.016 V 0.008 V 0.008 0.016 2 2 0.016 1 N4 N4 4 2 0.03 1 N4 N4 2 2 0.03 0.016 0.03 0.03 4 2 0.06 1 4 4 2 2 0.03
V 0.008 to 0.5 V 0.008 to 2 0.016 to 2 0.06 to N 4 0.25 to N 4 V 0.008 to 0.016 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.06 to N 4 0.25 to N 4 V 0.008 to 0.03 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.12 to 2 0.5 to 2 V 0.008 to 0.03 V 0.008 to 0.03 V 0.008 to 0.12 V 0.008 to 0.25 0.016 to 2 0.06 to 2 V 0.008 to 0.06 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.03 to 4 0.12 to 2 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.03 to N 4 0.12 to N 4 V 0.008 to 0.06 V 0.008 to 0.016 V 0.008 to 0.03 V 0.008 to 0.06 0.03 to 4 0.12 to N 4 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.016 to N 4 0.06 to N 4 V 0.008 to 0.06
/ 80.0/20.0 / 20.0/20.0 20.0/20.0 100.0/ / 28.0/64.0 / 8.0/44.0 12.0/20.0 100.0/ / 92.0/8.0 / 0.0/8.0 0.0/8.0 100.0/ / 97.2/0.0 / 8.3/16.7 52.8/16.7 100.0/ / 86.7/13.3 / 20.0/13.3 46.7/13.3 100.0/ / 67.1/32.9 / 2.9/14.3 22.9/21.4 100.0/ / 100.0/0.0 / 4.2/45.8 12.5/41.7 100.0/ / 76.5/22.0 / 6.0/21.5 24.5/20.5 100.0/
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the MIC results of the fluoroquinolones or the enzymestable h-lactam tested. In fact, MIC90 was z 2-fold lower for the penicillinase-positive compared with the penicillinase-negative strains for all 4 agents: gemifloxacin, ciprofloxacin, levofloxacin, and ceftriaxone. Tetracycline MIC values were z 4-fold higher for the penicillinase-positive compared with the penicillinase-negative strains (MIC50 = 2 versus 0.5 Ag/mL and MIC90 N 4 versus 2 Ag/mL). The majority of the gonococcal isolates (94.4%) had reduced susceptibility to penicillin (MIC z 0.12 Ag/mL; Table 2). Increasing resistance to penicillin was associated with elevated MIC50 and MIC90 values for gemifloxacin and the 5-comparators analyzed. The rank order of the antimicrobials with the highest difference in the MIC90 values between the penicillin-susceptible and penicillin-resistant strains was ciprofloxacin and levofloxacin (32-fold) N ceftriaxone and gemifloxacin (16-fold) N tetracycline (8-fold). Gemifloxacin MIC90 values increased from 0.06 Ag/mL for penicillin-susceptible to 1 Ag/mL for penicillin-intermediate and penicillin-resistant strains. 3.3. Activity of gemifloxacin and 5 comparators categorized by ciprofloxacin susceptibility More than a third of the isolates (97, 38.8%) had reduced susceptibility to ciprofloxacin, with 18.8% of strains having intermediate susceptibility (0.12-0.5 Ag/mL) and 20.0% resistant ( z 1 Ag/mL; see Table 2). Activity of gemifloxacin was negatively affected by increasing ciprofloxacin and levofloxacin MIC; MIC90 value was 128-fold higher (2 versus 0.016 Ag/mL) for ciprofloxacin-resistant versus susceptible strains, indicating cross resistance. The activity of ceftriaxone remained unaffected, with an identical MIC90 value (0.03 Ag/mL) for the ciprofloxacin-susceptible and ciprofloxacin-resistant strains. 3.4. Activity of gemifloxacin and 5 comparator antimicrobial agents against recent clinical isolates Analysis of 200 recent clinical isolates from 2004 (Table 3; 176 from 6 states and 24 bacteremic strains) revealed that gemifloxacin had an identical MIC90 value (1 Ag/mL) to that obtained for the entire collection. The rank order of the antimicrobials with the highest rates of nonsusceptible isolates (intermediate and resistant) was penicillin (94.0%) N tetracycline (75.5%) N ciprofloxacin (23.5%) N ceftriaxone (0.0%). The potency of gemifloxacin (MIC90 = 1 Ag/mL) was clearly at a level between that of ceftriaxone (0.03 Ag/mL) and older quinolones (4 Ag/mL). The antibiograms of the 176 clinical strains from 6 US states and the 24 bacteremic isolates are listed in Table 3. The number of isolates from each state varied between 5 (California) and 70 (Washington) and there was a preselection bias toward QRNG. There was a definite impact of geographical distribution on the endemic antimicrobial susceptibility rates. Penicillin susceptibility rates for the isolates from all 6 states was V 20.0% and ranged from 0.0% (New York) to a maximum of 20.0% (California and
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Oregon), and tetracycline susceptibility rates varied from 0.0% (New York) to 52.8% (Ohio). Ciprofloxacin susceptibility rates varied enormously, ranging from 28.0% (Hawaii) to greater than 90.0% (New York and Ohio). High-level ciprofloxacin resistance (MIC z 1 Ag/mL) was documented in the gonococcal isolates from 5 of the 6 states, ranging from 8.0% (New York) to more than 30.0% (Washington and Hawaii), but was absent in Ohio. Resistance to ciprofloxacin was also not detected among the isolates from bacteremic infections. 3.5. Activity of gemifloxacin and 5 comparators against previously characterized QRNG strains The 50 QRNG strains isolated in the Far East (Table 2; 29 with documented mutations in the QRDR region) were analyzed independently. The gemifloxacin MIC50 and MIC90 values were 0.06 and 0.25 Ag/mL, respectively, and the highest MIC was only 1 Ag/mL. These strains isolated in the 1990s generally had an intermediate range of MIC results to the monitored fluoroquinolones, and only 12.0% of the 50 strains had a resistant ciprofloxacin MIC. This is in clear contrast to the recent QRNG isolates (Section 3.4), which were predominantly high-level resistant (ciprofloxacin MIC z 1 Ag/mL). Levofloxacin appears to have equal clinical potential to that observed for ciprofloxacin, if adjusted to ofloxacin breakpoints (data not shown). 4. Discussion The nature and epidemiology of antimicrobial resistance in N. gonorrhoeae is a dynamic process evolving continually under selection pressures principally from (1) exposure to different classes of antimicrobial agents (Tapsall, 2001) and (2) change in behavior patterns of humans, the only reservoir for gonococci (CDC, 2002a, 2002b; Newman et al., 2004; World Health Organization [WHO], 2003). N. gonorrhoeae, adept at genetic recombination, has successfully acquired resistance to all the recommended therapeutic agents (CDC, 2002a). Plasmid-mediated penicillinase- producing and high-level tetracycline resistances (PPNG and TRNG, respectively) followed by chromosomally mediated resistance to these agents (CMRNG) in the 1970s, rendered these treatment regimens obsolete (Tapsall, 2001). Recommendation of fluoroquinolones as therapeutic agents in the last decade was soon followed by emergence and spread of QRNG strains with resistance rates of more than 90.0% in some countries in the Far East (WHO, 2003; Knapp et al., 1997; Ito et al., 2004; Kam et al., 1995). More recently, acquisition of resistance to highly effective cephalosporin agents (ceftriaxone and cefixime) has also been reported (Wang et al., 2003; Ito et al., 2004). Gonorrhoeae in individuals with a history of either foreign travel to areas of high QRNG prevalence or men who have sex with men has been recognized as risk factors for fluoroquinolone resistance, with recommendations to treat such individuals with either ceftriaxone or oral cefixime (CDC, 2002b).
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However, with the waxing and waning in the availability of cefixime, there is an urgent need for a safe, alternative highly effective ( N 95.0% cure rate; b 5.0% reported resistance) antigonococcal agent that can be administered orally, preferably with a single-dose regimen (CDC, 2002b). Our current study was performed to analyze the antigonococcal potency of gemifloxacin against a carefully selected sample of gonococcal isolates including contemporary strains (2004) from 6 sentinel sites in the United States where QRNG has occurred, enriched with isolates harboring established resistance phenotypes (PPNG, TRNG, CMRNG, and historic QRNG strains). Our results confirm that gemifloxacin continues to be most active in vitro among fluoroquinolones when tested against recent gonococcal isolates (MIC50 = 0.016 Ag/mL and MIC90 = 1 Ag/mL). Despite the preselection bias toward antimicrobial-resistant gonococcal isolates (entire collection QRNG rate of 38.8%, and high-level penicillin and tetracycline rates of 31.2% and 23.6%, respectively), the potency of gemifloxacin was competitive and positioned between that of ceftriaxone and older quinolones, penicillin, and tetracycline. Also corroborating the earlier reports (Jones et al., 2000a, 2000b), the activity of gemifloxacin was not affected by penicillinase production (PPNG), and the MIC90 value was 2-fold lower for penicillinase-positive when compared with the penicillinase-negative strains (0.5 versus 1 Ag/mL) (Berron et al., 2000; Jones et al., 2002a). Although the reported PPNG rates are more than 50.0% in certain countries of the southeast Asian and western Pacific regions, a decline in the PPNG rates has been noted recently in certain parts of the world including the United States (11.1% in 1991 to 1.0% in 2003) and Japan (7.9% in 1993–1994 to 2.0% in 1997–1998) (CDC, 2002b; Tanaka et al., 2000a; Tapsal et al., 2001; WHO, 2003). Investigators in Hong Kong, analyzing N. gonorrhoeae strains over a 2-year period (1992–1994), noted that the emergence of QRNG was associated with a rapid decline of rates of both PPNG and TRNG and attributed this decline to the bplasmid-curingQ effect of fluoroquinolones (Kam et al., 1995). However, increasing penicillin MIC was associated with z 8-fold increase in the MIC90 value of gemifloxacin and its comparators (ciprofloxacin, levofloxacin, ceftriaxone, and tetracycline), but the highest gemifloxacin MIC was only 2 Ag/mL. Occurrence of coresistance in gonococcal isolates resulting in increase in MIC values of structurally unrelated compounds such as h-lactams, tetracyclines, and fluoroquinolones has been reported previously (Tanaka et al., 2000a, 2000b, 2004; Dewi et al., 2004). It is recognized that coexistence of chromosomal mutations in the QRDR region contributing to fluoroquinolone resistance (gyrA with or without parC mutations) along with recognized chromosomal mutations in other loci like penA (decreased binding to PBP2), penB (reduced porin permeability conferring reduced susceptibility to penicillin, tetracycline, and quinolones), and mtr (multidrug efflux pump) can result in multidrug resistance in gonococcal isolates (Tanaka et al.,
2004). Testing 131 recent clinical N. gonorrhoeae isolates from Japan (72.5% QRNG), investigators noted that 71.0% of the strains carried mutations in both gyrA gene and mtrR coding sequence, substantiating the simultaneous occurrence of mutations in the QRDR regions and MtrRCDE efflux system (Dewi et al., 2004). Although cross-resistance among the various fluoroquinolones is well recognized, it is recommended that fluoroquinolones be analyzed independently due the differential target affinities (DNA gyrase and topoisomerase IV) of each compound, resulting in varying potencies (Berron et al., 2000; Jones et al., 2000a; Tanaka et al., 2000b). Although the MIC90 value of gemifloxacin was 128-fold higher for the ciprofloxacin-resistant compared with the ciprofloxacin-susceptible strains (2 versus 0.016 Ag/mL), the gemifloxacin MIC90 value was z 2-fold lower than that for the older quinolones analyzed for the QRNG strains. Analyzing 85 gonococcal isolates from Japan (20 with no mutations in QRDR region, 43 with mutations in gyrA alone, and 22 with mutations in both gyrA and parC regions), the investigators reported that gemifloxacin showed the strongest activity against all 3 subsets of strains compared with 6 other fluoroquinolones (ciprofloxacin, levofloxacin, norfloxacin, tosufloxacin, trovafloxacin, and sparfloxacin) (Tanaka et al., 2000b). Gemifloxacin retained potency against strains with a single gyrA mutation (MIC = 0.004– 0.06 Ag/mL) and those with 2 or 3 mutations within gyrA and parC (MIC = 0.03– 0.25 Ag/mL), and the superior activity was attributed to stronger inhibitory activity of GyrA and ParC proteins in comparison with the other quinolones (Morrissey and Tillotson, 2004; Tanaka et al., 2000b). It has also been reported that due to the bdualtargetingQ action of gemifloxacin, selection of resistant mutants during treatment would be less likely, and the anticipated incidence of spontaneous mutation was only 1 in 1012 to 1014 (File and Iannini, 2003; Ruiz et al., 2001). The 2 factors that are recognized to influence the antibiograms of gonococcal isolates are exposure time and geographic distribution (Tapsall, 2001). The resistance mechanism to quinolones in gonococci has been mainly due to chromosomal mutations in the target QRDR regions that develops incrementally, with stepwise accrual of chromosomal changes over a period resulting in gradual increase in the quinolone MIC (Tapsall, 2001). This observation was exemplified in the 50 historic QRNG strains isolated more than a decade ago in Japan and further analyzed in this study (Deguchi et al., 1995, 1996). These gonococci in which QRDR changes resulting in quinolone resistance was demonstrated for the first time had predominantly intermediate-level susceptibility to ciprofloxacin (88.0%), and correspondingly, the majority of the strains had a single mutation in gyrA (19/29 strains with QRDR changes, 65.5%) (Deguchi et al., 1996). This was in contrast to the 200 contemporary strains from 2004 analyzed in this study, where 93.6% (47/200 strains) of the QRNG strains were fully resistant to ciprofloxacin. This
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shift in the degree of reduced susceptibility to ciprofloxacin, resulted in a corresponding 4-fold increase in the MIC90 value of gemifloxacin over 10 years (1 versus 0.25 Ag/mL; Tables 2 and 3). The impact of the geographical distribution on the endemic antimicrobial susceptibility rates of gonococci recognized by the surveillance studies conducted worldwide and in United States was also evident from the 6 sentinel sites (states) in United States cited here (CDC, 2004a, 2004b; Tapsall et al., 2001; WHO, 2003). The ciprofloxacin resistance (MIC z 1 Ag/mL) rates for the states on the Pacific Coast (California, Oregon, and Washington) and Hawaii were very elevated, ranging from 13.3% (Oregon) to z 32.9% (Washington and Hawaii). These findings are in accord with the surveillance report from the Gonococcal Isolate Surveillance Project, where testing of 6,552 gonococcal isolates from 30 participating cities across the United States in 2003 found a staggering two thirds (186 strains) of the 4.1% isolates (270 total) resistant to ciprofloxacin were from California (CDC, 2004a). Similarly, an increase in the proportion of isolates resistant to ciprofloxacin among Gonococcal Isolate Surveillance Project isolates was also noted in Seattle (6.9% in 2003 versus 3.0% in 2002) and in Honolulu (13.3% in 2003 versus 11.7% in 2002) (CDC, 2004a). Irrespective of the high rates of ciprofloxacin resistance in our study, gemifloxacin remained most active against these strains (MIC90 V 0.008–1 Ag/mL). In contrast, to the high QRNG rates noted in the western states, the bacteremic isolates (24 strains) were exquisitely susceptible to the quinolones analyzed (ciprofloxacin, levofloxacin, and gemifloxacin MIC 90 V 0.03 Ag/mL) and ceftriaxone (MIC90 0.06 Ag/mL). This finding substantiates the report that a majority of the QRNG isolates are proline-requiring autotypes compared with bacteremic strains, which require arginine-hypoxanthine–uracil (Tanaka et al., 2004). In conclusion, our results confirm the high activity of gemifloxacin in comparison to the other fluoroquinolones analyzed against the collection of contemporary strains of N. gonorrhoeae, irrespective of the resistance mechanism or phenotype. Gemifloxacin with its documented potency, should be considered for further development as an antigonococcal agent to treat emerging strains that are resistant to penicillins, tetracycline, and some older fluoroquinolones or have become less responsive to azithromycin (Yong et al., 1997). Gemifloxacin concentrations in genitourinary tract tissues (KG Naber, Oscient Pharmaceuticals Report, data on file, 2005) indicates the following levels after a 320-mg dose: plasma C max (1.25 Ag/mL), ejaculate (1.4 – 8.0 Ag/mL; z 3 plasma concentration), prostatic fluid (0.119–3.12 Ag/mL), and vaginal secretions (15% of plasma concentration). The urinary excretion was 28% (elimination half-life, 25 h) compared with 81% for the ofloxacin control. Single-dose or short-course gemifloxacin regimens should be evaluated as dictated by pharmacokinetic/pharmacodynamic modeling.
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Acknowledgments The coauthors express their gratitude to the following contributors to this investigation: L Deshpande, DJ Biedenbach, MG Stilwell, and KL Meyer. We also thank Joseph DiPersio (Summa Health Systems), Dwight Hardy (University of Rochester Medical Center), Judy Fusco (TPMG Regional Laboratory— San Francisco), Sue Swanzy (University of Washington), and William Whittington (Hartonview Medical Center) for their assistance in the collection of recent clinical isolates. This study was sponsored by an educational/research grant by Replidyne, Inc. References Appelbaum PC, Hunter PA (2000) The fluoroquinolone antibacterials: past, present and future perspectives. Int J Antimicrob Agents 16:5 – 15. Appelbaum PC, Gillespie SH, Burley CJ, Tillotson GS (2004) Antimicrobial selection for community-acquired lower respiratory tract infections in the 21st century: a review of gemifloxacin. Int J Antimicrob Agents 23:533 – 546. Berron S, Vazquez JA, Giminez MJ, de la Fuente L, Aguilar L (2000) In vitro susceptibilities of 400 Spanish isolates of Neisseria gonorrhoeae to gemifloxacin and 11 other antimicrobial agents. Antimicrob Agents Chemother 44:2543 – 2544. Centers for Disease Control and Prevention (2002a) Discontinuation of cefixime tablets—United States. MMWR Morb Mortal Wkly Rep 51:1052. Centers for Disease Control and Prevention (2002b) Sexually transmitted diseases treatment guidelines 2002. MMWR Morb Mortal Wkly Rep 51(RR-6):1 – 78. Centers for Disease Control and Prevention (2004a) Increases in fluoroquinolone-resistant Neisseria gonorrhoeae among men who have sex with men—United States, 2003, and revised recommendations for gonorrhoea treatment, 2004. MMWR Morb Mortal Wkly Rep 53:335 – 338. Centers for Disease Control and Prevention (2004b) Sexually Transmitted Disease Surveillance 2003 Supplement: Gonococcal Isolate Surveillance Project (GISP) Annual Report—2003. Atlanta (GA)7 US Department of Health and Human Services. Clinical and Laboratory Standards Institute (2005) Performance standards for antimicrobial susceptibility testing 15th Informational Supplement M100-S15. Wayne (PA)7 CLSI. Deguchi T, Yasuda M, Asano M, Tada K, Iwata H, Komeda H, Ezaki T, Saito I, Kawada Y (1995) DNA gyrase mutations in quinolone-resistant clinical isolates of Neisseria gonorrhoeae. Antimicrob Agents Chemother 39:561 – 563. Deguchi T, Yasuda M, Nakano M, Ozeki S, Ezaki T, Saito I, Kawada Y (1996) Quinolone-resistant Neisseria gonorrhoeae: correlation of alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV with antimicrobial susceptibility profiles. Antimicrob Agents Chemother 40:1020 – 1023. Dewi BE, Akira S, Hayashi H, Ba-Thein W (2004) High occurrence of simultaneous mutations in target enzymes and MtrRCDE efflux system in quinolone-resistant Neisseria gonorrhoeae. Sex Transm Dis 31: 353 – 359. Emmerson AM, Jones AM (2003) The quinolones: decades of development and use. J Antimicrob Chemother 51:13 – 20. File Jr TM, Iannini PB (2003) A profile of gemifloxacin, a new respiratory fluoroquinolone. Today’s Ther Trends 21:415 – 435. Ito M, Yasuda M, Yokoi S, Ito S, Takahashi Y, Ishihara S, Maeda S, Deguchi T (2004) Remarkable increase in central Japan in 2001–2002 of Neisseria gonorrhoeae isolates with decreased susceptibility to penicillin, tetracycline, oral cephalosporins, and fluoroquinolones. Antimicrob Agents Chemother 48:3185 – 3187.
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Jones RN, Deshpande LM, Erwin ME, Barrett MS, Beach ML (2000a) Anti-gonococcal activity of gemifloxacin against fluoroquinoloneresistant strains and a comparison of agar dilution and Etest methods. J Antimicrob Chemother 45:67 – 70. Jones RN, Erwin ME, The Quality Control Study Group (2000b) Development of gemifloxacin in vitro susceptibility test methods for gonococci including quality control guidelines. Diagn Microbiol Infect Dis 37:195 – 201. Jones RN (2002) Microbiology of newer fluoroquinolones: focus on respiratory pathogens. Diagn Microbiol Infect Dis 44:213 – 220. Kam KM, Lo KK, Ho NK, Cheung MM (1995) Rapid decline in penicillinase-producing Neisseria gonorrhoeae in Hong Kong associated with emerging 4-fluoroquinolone resistance. Genitourin Med 71:141 – 145. Knapp JS, Fox KK, Trees DL, Whittington WL (1997) Fluoroquinolone resistance in Neisseria gonorrhoeae. Emerg Infect Dis 3:33 – 39. Lowe MN, Lamb HM (2000) Gemifloxacin. Drugs 59:1137 – 1148. Morrissey I, Tillotson G (2004) Activity of gemifloxacin against Streptococcus pneumoniae and Haemophilus influenzae. J Antimicrob Chemother 53:144 – 148. National Committee for Clinical Laboratory Standards (2003) Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically Document M7-A6. Wayne (PA)7 NCCLS. Newman LM, Wang SA, Olhye RG, O’Connor N, Lee MV, Weinstock HS (2004) The epidemiology of fluoroquinoloneresistant Neisseria gonorrhoeae in Hawaii, 2001. Clin Infect Dis 38:649 – 654. Ruiz J, Jurado A, Garcia-Mendez E, Marco F, Aguilar L, Jimenez De Anta MT, Vila J (2001) Frequency of selection of fluoroquinolone-resistant
mutants of Neisseria gonorrhoeae exposed to gemifloxacin and four other quinolones. J Antimicrob Chemother 48:545 – 548. Tanaka M, Nakayama H, Haraoka M, Saika T, Kobayashi I, Naito S (2000a) Antimicrobial resistance of Neisseria gonorrhoeae and high prevalence of ciprofloxacin-resistant isolates in Japan, 1993 to 1998. J Clin Microbiol 38:521 – 525. Tanaka M, Tunoe H, Mochida O, Kanayama A, Saika T, Kobayashi I, Naito S (2000b) Antimicrobial activity of gemifloxacin (SB-265805), a newer fluoroquinolone, against clinical isolates of Neisseria gonorrhoeae, including fluoroquinolone-resistant isolates. Diagn Microbiol Infect Dis 38:109 – 113. Tanaka M, Nakayama H, Notomi T, Irie S, Tsunoda Y, Okadome A, Saika T, Kobayashi I (2004) Antimicrobial resistance of Neisseria gonorrhoeae in Japan, 1993–2002: continuous increasing of ciprofloxacinresistant isolates. Int J Antimicrob Agents 24S:S15 – S22. Tapsall J (2001) Antimicrobial resistance in Neisseria gonorrhoeae WHO/CDS/DRS/2001.3:16. Geneva (Switzerland)7 World Health Organization. Wang SA, Lee MV, O’Connor N, Iverson CJ, Ohye RG, Whiticar PM, Hale JA, Trees DL, Knapp JS, Effler PV, Weinstock HS (2003) Multidrugresistant Neisseria gonorrhoeae with decreased susceptibility to cefixime, Hawaii, 2001. Clin Infect Dis 37:849 – 852. World Health Organization Western Pacific Gonococcal Antimicrobial Surveillance Programme (2003) Surveillance of antibiotic resistance in Neisseria gonorrhoeae in the World Health Organization Western Pacific Region, 2002. Commun Dis Intell 27:488 – 491. Yong H, Moyes A, McMillan A (1997) Azithromycin- and erythromycinresistant Neisseria gonorrhoeae following treatment with azithromycin. Int J STD AIDS 8:299 – 302.
Antimicrobial susceptibility studies
Activity of gemifloxacin tested against Neisseria gonorrhoeae isolates including antimicrobial-resistant phenotypes Sudha Pottumarthya, Thomas R. Fritschea, Ronald N. Jonesa,b,T a
Jones Microbiology Institute Laboratories, North Liberty, IA 52317, USA b Tufts University School of Medicine, Boston, MA, USA Received 29 June 2005; accepted 29 August 2005
Abstract The antigonococcal potency of gemifloxacin and 5 reference comparator antimicrobials was determined for a selected collection of gonococcal isolates. The 250 Neisseria gonorrhoeae strains were inclusive of (1) 50 historic strains from Japan with elevated fluoroquinolone minimal inhibitory concentration values (QRNG) and (2) 200 contemporary strains from clinical specimens in 2004 (176 from 6 sentinel sites in the United States and 24 bacteremic isolates from the SENTRY Antimicrobial Surveillance Program). The rank order of potency of the tested antimicrobials for the entire collection was: ceftriaxone (MIC90 = 0.06 Ag/mL) N gemifloxacin (1 Ag/mL) N tetracycline (2 Ag/mL) N ciprofloxacin = levofloxacin = penicillin (4 Ag/mL). The activity of gemifloxacin was not affected by penicillinase production; however, its activity was decreased for penicillin-resistant strains. Cross-resistance between gemifloxacin and the older fluoroquinolones was present, and the gemifloxacin MIC90 value was higher for the ciprofloxacin-resistant strains compared with the ciprofloxacin-susceptible strains (2 versus 0.016 Ag/mL, respectively). More than 20.0% of the recent clinical strains were resistant to penicillin, tetracycline, and ciprofloxacin with N 30.0% of gonococci resistant to ciprofloxacin in Washington State and Hawaii. The historic QRNG strains from the Far East were predominantly of intermediate susceptibility (88.0%) to ciprofloxacin, with a gemifloxacin MIC90 value of only 0.25 Ag/mL. The bacteremic gonococcal strains were exquisitely susceptible to the 3 quinolones tested (ciprofloxacin, levofloxacin, and gemifloxacin, MIC90 at V 0.03 Ag/mL) and ceftriaxone (MIC90 = 0.06 Ag/mL). In summary, the potency of gemifloxacin was competitive and positioned between that of ceftriaxone and older quinolones or penicillin or tetracycline, irrespective of the gonococcal resistance phenotype. Gemifloxacin should be considered for further development as a therapeutic option to treat uncomplicated infections due to emerging strains resistant to penicillins, tetracycline, and some older fluoroquinolones. D 2006 Elsevier Inc. All rights reserved. Keywords: Gemifloxacin; N. gonorrhoeae; SENTRY program; Fluoroquinolones; Resistance; Ceftriaxone
1. Introduction Over 4 decades of directed research and development in the field of quinolones have led to the development of a new group of bnovelQ or brespiratoryQ fluoroquinolones (Appelbaum and Hunter, 2000; Emmerson and Jones, 2003). These new compounds developed for the 21st century, follow a better understanding of structure–activity relationships and are characterized by enhanced activity against Gram-positive cocci, especially Streptococcus pneumoniae, as well as many intracellular pathogens, while retaining
T Corresponding author. Jones Microbiology Institute Laboratories, 345 Beaver Kreek Centre, Suite A, North Liberty, IA 52317, USA. Tel.: +1319-665-3370; fax: +1-319-665-3371. E-mail address: [email protected] (R.N. Jones). 0732-8893/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2005.08.013
excellent activity against Gram-negative organisms (Emmerson and Jones, 2003; Jones, 2002). Gemifloxacin (formerly SB265805, LB20304) represents one such synthetic broad-spectrum fluoronaphthyridone with high affinity for both fluoroquinolone target enzymes (DNA gyrase and topoisomerase IV) at therapeutically achievable drug concentrations (Lowe and Lamb, 2000; Morrissey and Tillotson, 2004). This bdual-targetingQ action of gemifloxacin confers higher in vitro activity against first- and second-step fluoroquinolone-resistant mutants of pneumococci compared with the other marketed fluoroquinolones analyzed (Appelbaum et al., 2004; File and Iannini, 2003). Studies conducted in the late 1990s testing clinical strains of Neisseria gonorrhoeae, including strains with reduced susceptibility to quinolones (QRNG), established the higher potency of gemifloxacin (Berron et al., 2000; Jones et al.,
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2000a, 2000b; Tanaka et al., 2000a, 2000b). Testing 150 clinical strains of gonococci, 33.3% of which had an elevated ciprofloxacin minimal inhibitory concentration (MIC; 43 intermediate susceptibility [MIC = 0.12– 0.5 Ag/mL] and 7 resistant [MIC z 1 Ag/mL] obtained from Japan, United States, and the Netherlands), the authors found a gemifloxacin MIC90 result of 0.12 Ag/mL that was lower than those recorded for trovafloxacin (0.25 Ag/mL) and for moxifloxacin or grepafloxacin (0.5 Ag/mL) (Jones et al., 2000a). Similarly in Japan, testing 94 consecutive clinical isolates of N. gonorrhoeae from 1992 to 1993 and 100 isolates from 1996 to 1997 (including 31 ciprofloxacinresistant strains), Tanaka et al. (2000a, 2000b) substantiated the higher potency of gemifloxacin with MIC90 values of 0.03 and 0.12 Ag/mL, respectively. This was in contrast to the MIC90 values of 0.12– 0.25 Ag/mL (for 1992–1993 isolates) and from 0.5 to 2 Ag/mL (for 1996–1997 isolates) of the other fluoroquinolones analyzed (sparfloxacin, trovafloxacin, tosufloxacin, and levofloxacin) (Tanaka et al., 2000a, 2000b). However, the authors also noted that the gemifloxacin MIC90 value for the 1996–1997 isolates was 4-fold higher than that for the 1992–1993 isolates (0.12 versus 0.03 Ag/mL), and that the MIC90 values for the comparator fluoroquinolones were 2- to 8-fold greater for the 1996 –1997 isolates, reiterating the need for continued resistance surveillance among gonococci (Tanaka et al., 2000a, 2000b). To evaluate if gemifloxacin has retained its superior potency among fluoroquinolones against gonococcal isolates, which have since evolved further and developed higher levels of resistance to fluoroquinolones, we tested a collection of 250 N. gonorrhoeae isolates. The collection was chosen to represent well-characterized genotypes of QRNG, multiple phenotypes of h-lactam, tetracycline, and QRNG resistance, and a sample of recent clinical isolates (2004) of N. gonorrhoeae isolated from blood cultures and also from 6 distinct geographic locations in the United States, where QRNG has been reported to be endemic/ epidemic (Centers for Disease Control and Prevention [CDC], 2002a, 2002b, 2004a, 2004b; Wang et al., 2003).
2. Materials and methods
(36, 20.5%), Oregon (15, 8.5%), and Washington (70, 39.8%). More than one fourth of the strains from the entire collection (74, 29.6%) had well-characterized resistance phenotypes by mechanisms analysis: 50 QRNG isolates, 14 strains resistant to penicillin and tetracycline, and 10 isolates with intermediate susceptibility to penicillin. The QRNG strains were isolated in the Far East and characterized in Japan (courtesy of Professors Tanaka and Deguchi). More than half (29, 58.0%) of these QRNG strains have documented mutations in the quinoloneresistance–determining regions (QRDR) with (1) a single amino acid substitution in gyrA (19 strains), (2) single substitution in both gyrA and parC (7 strains), and (3) double amino acid substitution in gyrA and a single mutation in parC (3 strains) (Deguchi et al., 1995, 1996). 2.2. Susceptibility testing methods MICs of 6 antimicrobial agents were determined by the reference agar dilution method using GC agar base supplemented with a defined supplement (National Committee for Clinical Laboratory Standards, 2003). The antimicrobial agents tested were: gemifloxacin (Oscient Pharmaceuticals, MA), ciprofloxacin, levofloxacin, penicillin, tetracycline, and ceftriaxone. The results were interpreted according to the criteria of the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) (CLSI, 2005). The following quality control strains were used to validate the study: N. gonorrhoeae ATCC 49226 and Staphylococcus aureus ATCC 29213 (CLSI, 2005). 2.3. Data analysis The results were analyzed to determine the effect of the various resistance mechanisms, such as penicillinase production and penicillin and fluoroquinolone susceptibility category on the activity of gemifloxacin and its peer drugs. The results were also stratified to analyze the effect of geographical distribution and isolation from blood on the antimicrobial susceptibility profiles of the gonococcal isolates. The activity of the antimicrobials against the historic QRNG gonococcal isolates from the Far East (Tanaka et al., 2000a, 2000b, 2004; Deguchi et al., 1995, 1996) was analyzed separately.
2.1. Strain collection The selected collection of 250 N. gonorrhoeae clinical isolates included 176 (70.4%) recent strains isolated from clinical specimens in 2004 from geographic sites in the United States, 24 recent clinical bacteremic strains from the SENTRY Antimicrobial Surveillance Program, and 50 historic QRNG Japanese strains from the Jones Microbiology Institute (North Liberty, IA) laboratories’ collection were analyzed. The clinical strains were obtained from 6 geographically distinct sites in the United States where QRNG has been reported to be endemic/epidemic, which includes California (5 strains, 2.8% of recent clinical isolates), Hawaii (25, 14.2%), New York (25, 14.2%), Ohio
Table 1 Gemifloxacin activity compared with reference agents when tested against 250 strains of N. gonorrhoeae Antimicrobial agent Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
MIC (Ag/mL)
Susceptible/ resistant (%)a
50%
90%
Range
0.016 V 0.008 0.016 1 0.5 V 0.008
1 4 4 4 2 0.06
V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.016 to N 4 0.06 to N 4 V 0.008 to 0.12
/ 61.2/20.0 / 5.6/31.2 19.6/23.6 100.0/
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005).
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3. Results 3.1. Activity of gemifloxacin and 5 comparator antimicrobial agents against N. gonorrhoeae Gemifloxacin MIC results were compared with 5 antimicrobials commonly used as reference agents (Table 1).
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The rank order of potency of these antimicrobials for the entire collection (250 isolates) was ceftriaxone (MIC90 = 0.06 Ag/mL) N gemifloxacin (1 Ag/mL) N tetracycline (2 Ag/mL) N ciprofloxacin = levofloxacin = penicillin (4 Ag/mL). Using MIC90 for comparison, gemifloxacin was consistently 4-fold more potent than the other quinolones
Table 2 Comparative gemifloxacin activity tested against N. gonorrhoeae isolates having defined resistance mechanisms or interpretive categories for h-lactams and ciprofloxacin Organism group (no. tested)
Penicillin Susceptible (14)
Intermediate (158)
Resistant (78)
h-Lactamase–positive (28)
h-Lactamase–negative (222)
Ciprofloxacin Susceptible (153)
Intermediate (47)
Resistant (50)
Nonsusceptible (50)b
Antimicrobial agent
MIC (Ag/mL)
Susceptible/ resistant (%)a
50%
90%
Range
Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Tetracycline Ceftriaxone
V 0.008 V 0.008 0.016 0.25 V 0.008 V 0.008 V 0.008 0.016 0.5 V 0.008 0.06 0.25 0.25 2 0.03 0.06 0.25 0.25 2 V 0.008 V 0.008 V 0.008 0.016 0.5 V 0.008
0.06 0.12 0.12 0.5 V 0.008 1 4 4 1 0.016 1 N4 N4 4 0.12 0.5 2 2 N4 0.03 1 4 4 2 0.06
V 0.008 to 0.06 V 0.008 to 0.12 V 0.008 to 0.25 0.06 to 0.5 V 0.008 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.12 to N 4 V 0.008 to 0.12 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.25 to N 4 V 0.008 to 0.12 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.25 to N 4 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.06 to N 4 V 0.008 to 0.12
/ 85.7/0.0 / 85.7/0.0 100.0/ / 74.1/19.0 / 22.8/7.0 100.0/ / 30.8/25.6 / 1.3/61.5 100.0/ / 32.1/25.0 / 3.6/64.3 100.0/ / 64.9/19.4 / 21.6/18.5 100.0/
Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
V 0.008 0.016 0.25 0.5 V 0.008 0.06 0.25 2 1 0.03 1 4 1 1 0.016 0.06 0.25 0.25 2 1 0.03
0.016 0.03 2 2 0.03 0.12 0.5 N4 2 0.12 2 N4 N4 4 0.03 0.25 1 1 N4 2 0.12
V 0.008 to 0.016 V 0.008 to 0.06 0.016 to N 4 0.06 to N 4 V 0.008 to 0.06 0.016 to 0.25 0.12 to 0.5 0.03 to N 4 0.5 to N 4 V 0.008 to 0.12 0.06 to 2 0.06 to N 4 0.25 to N 4 0.12 to N 4 V 0.008 to 0.06 0.03 to 1 0.12 to N 4 0.12 to 4 0.03 to N 4 0.5 to 4 V 0.008 to 0.12
/ / 7.8/15.7 31.4/14.4 100.0/ / / 4.3/72.3 0.0/31.9 100.0/ / / 0.0/40.0 2.0/44.0 100.0/ / 0.0/12.0 / 4.0/70.0 0.0/36.0 100.0/
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005). b Fifty Far East clinical isolates from 1994 to 1997 with defined QRDR changes.
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tested (1 versus 4 Ag/mL), and the highest gemifloxacin MIC recorded was only 2 Ag/mL. The QRNG rate was 38.8% and high-level penicillin and tetracycline resistance rates were elevated at 31.2% and 23.6% respectively. No isolates were resistant to the parenteral cephalosporin (ceftriaxone) tested.
3.2. Activity of gemifloxacin and 5 comparators categorized by b-lactam susceptibilities Penicillinase-producing N. gonorrhoeae (PPNG) constituted 11.2% of the collection tested (Table 2). Production of the penicillinase did not result in any adverse changes in
Table 3 Gemifloxacin and 5 comparison agents tested against recent (2004) genital and blood culture isolates listed by geographic area (United States) or specimen source Organism group (no. tested)
Antimicrobial agent
California (5)
Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone Gemifloxacin Ciprofloxacin Levofloxacin Penicillin Tetracycline Ceftriaxone
MIC (Ag/mL) 50%
Hawaii (25)
New York (25)
Ohio (36)
Oregon (15)
Washington (70)
Bacteremia (24)
All clinical cases (200)
= no interpretive criteria have been determined for this agent. a Interpretive criteria as published by the CLSI (2005).
V 0.008 V 0.008 0.016 1 0.5 V 0.008 0.5 4 2 1 1 V 0.008 0.016 V 0.008 0.016 0.25 0.5 V 0.008 V 0.008 V 0.008 0.016 0.25 0.25 V 0.008 V 0.008 V 0.008 0.016 0.25 0.5 V 0.008 V 0.008 V 0.008 0.016 0.5 0.5 V 0.008 V 0.008 0.016 0.016 1 1 0.016 V 0.008 V 0.008 0.016 0.5 0.5 V 0.008
Susceptible/ resistant (%)a 90%
Range
1 4 4 N4 N4 0.016 0.016 0.016 0.03 1 1 0.016 V 0.008 V 0.008 0.016 2 2 0.016 1 N4 N4 4 2 0.03 1 N4 N4 2 2 0.03 0.016 0.03 0.03 4 2 0.06 1 4 4 2 2 0.03
V 0.008 to 0.5 V 0.008 to 2 0.016 to 2 0.06 to N 4 0.25 to N 4 V 0.008 to 0.016 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.06 to N 4 0.25 to N 4 V 0.008 to 0.03 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.12 to 2 0.5 to 2 V 0.008 to 0.03 V 0.008 to 0.03 V 0.008 to 0.12 V 0.008 to 0.25 0.016 to 2 0.06 to 2 V 0.008 to 0.06 V 0.008 to 1 V 0.008 to N 4 V 0.008 to N 4 0.03 to 4 0.12 to 2 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.03 to N 4 0.12 to N 4 V 0.008 to 0.06 V 0.008 to 0.016 V 0.008 to 0.03 V 0.008 to 0.06 0.03 to 4 0.12 to N 4 V 0.008 to 0.06 V 0.008 to 2 V 0.008 to N 4 V 0.008 to N 4 0.016 to N 4 0.06 to N 4 V 0.008 to 0.06
/ 80.0/20.0 / 20.0/20.0 20.0/20.0 100.0/ / 28.0/64.0 / 8.0/44.0 12.0/20.0 100.0/ / 92.0/8.0 / 0.0/8.0 0.0/8.0 100.0/ / 97.2/0.0 / 8.3/16.7 52.8/16.7 100.0/ / 86.7/13.3 / 20.0/13.3 46.7/13.3 100.0/ / 67.1/32.9 / 2.9/14.3 22.9/21.4 100.0/ / 100.0/0.0 / 4.2/45.8 12.5/41.7 100.0/ / 76.5/22.0 / 6.0/21.5 24.5/20.5 100.0/
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the MIC results of the fluoroquinolones or the enzymestable h-lactam tested. In fact, MIC90 was z 2-fold lower for the penicillinase-positive compared with the penicillinase-negative strains for all 4 agents: gemifloxacin, ciprofloxacin, levofloxacin, and ceftriaxone. Tetracycline MIC values were z 4-fold higher for the penicillinase-positive compared with the penicillinase-negative strains (MIC50 = 2 versus 0.5 Ag/mL and MIC90 N 4 versus 2 Ag/mL). The majority of the gonococcal isolates (94.4%) had reduced susceptibility to penicillin (MIC z 0.12 Ag/mL; Table 2). Increasing resistance to penicillin was associated with elevated MIC50 and MIC90 values for gemifloxacin and the 5-comparators analyzed. The rank order of the antimicrobials with the highest difference in the MIC90 values between the penicillin-susceptible and penicillin-resistant strains was ciprofloxacin and levofloxacin (32-fold) N ceftriaxone and gemifloxacin (16-fold) N tetracycline (8-fold). Gemifloxacin MIC90 values increased from 0.06 Ag/mL for penicillin-susceptible to 1 Ag/mL for penicillin-intermediate and penicillin-resistant strains. 3.3. Activity of gemifloxacin and 5 comparators categorized by ciprofloxacin susceptibility More than a third of the isolates (97, 38.8%) had reduced susceptibility to ciprofloxacin, with 18.8% of strains having intermediate susceptibility (0.12-0.5 Ag/mL) and 20.0% resistant ( z 1 Ag/mL; see Table 2). Activity of gemifloxacin was negatively affected by increasing ciprofloxacin and levofloxacin MIC; MIC90 value was 128-fold higher (2 versus 0.016 Ag/mL) for ciprofloxacin-resistant versus susceptible strains, indicating cross resistance. The activity of ceftriaxone remained unaffected, with an identical MIC90 value (0.03 Ag/mL) for the ciprofloxacin-susceptible and ciprofloxacin-resistant strains. 3.4. Activity of gemifloxacin and 5 comparator antimicrobial agents against recent clinical isolates Analysis of 200 recent clinical isolates from 2004 (Table 3; 176 from 6 states and 24 bacteremic strains) revealed that gemifloxacin had an identical MIC90 value (1 Ag/mL) to that obtained for the entire collection. The rank order of the antimicrobials with the highest rates of nonsusceptible isolates (intermediate and resistant) was penicillin (94.0%) N tetracycline (75.5%) N ciprofloxacin (23.5%) N ceftriaxone (0.0%). The potency of gemifloxacin (MIC90 = 1 Ag/mL) was clearly at a level between that of ceftriaxone (0.03 Ag/mL) and older quinolones (4 Ag/mL). The antibiograms of the 176 clinical strains from 6 US states and the 24 bacteremic isolates are listed in Table 3. The number of isolates from each state varied between 5 (California) and 70 (Washington) and there was a preselection bias toward QRNG. There was a definite impact of geographical distribution on the endemic antimicrobial susceptibility rates. Penicillin susceptibility rates for the isolates from all 6 states was V 20.0% and ranged from 0.0% (New York) to a maximum of 20.0% (California and
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Oregon), and tetracycline susceptibility rates varied from 0.0% (New York) to 52.8% (Ohio). Ciprofloxacin susceptibility rates varied enormously, ranging from 28.0% (Hawaii) to greater than 90.0% (New York and Ohio). High-level ciprofloxacin resistance (MIC z 1 Ag/mL) was documented in the gonococcal isolates from 5 of the 6 states, ranging from 8.0% (New York) to more than 30.0% (Washington and Hawaii), but was absent in Ohio. Resistance to ciprofloxacin was also not detected among the isolates from bacteremic infections. 3.5. Activity of gemifloxacin and 5 comparators against previously characterized QRNG strains The 50 QRNG strains isolated in the Far East (Table 2; 29 with documented mutations in the QRDR region) were analyzed independently. The gemifloxacin MIC50 and MIC90 values were 0.06 and 0.25 Ag/mL, respectively, and the highest MIC was only 1 Ag/mL. These strains isolated in the 1990s generally had an intermediate range of MIC results to the monitored fluoroquinolones, and only 12.0% of the 50 strains had a resistant ciprofloxacin MIC. This is in clear contrast to the recent QRNG isolates (Section 3.4), which were predominantly high-level resistant (ciprofloxacin MIC z 1 Ag/mL). Levofloxacin appears to have equal clinical potential to that observed for ciprofloxacin, if adjusted to ofloxacin breakpoints (data not shown). 4. Discussion The nature and epidemiology of antimicrobial resistance in N. gonorrhoeae is a dynamic process evolving continually under selection pressures principally from (1) exposure to different classes of antimicrobial agents (Tapsall, 2001) and (2) change in behavior patterns of humans, the only reservoir for gonococci (CDC, 2002a, 2002b; Newman et al., 2004; World Health Organization [WHO], 2003). N. gonorrhoeae, adept at genetic recombination, has successfully acquired resistance to all the recommended therapeutic agents (CDC, 2002a). Plasmid-mediated penicillinase- producing and high-level tetracycline resistances (PPNG and TRNG, respectively) followed by chromosomally mediated resistance to these agents (CMRNG) in the 1970s, rendered these treatment regimens obsolete (Tapsall, 2001). Recommendation of fluoroquinolones as therapeutic agents in the last decade was soon followed by emergence and spread of QRNG strains with resistance rates of more than 90.0% in some countries in the Far East (WHO, 2003; Knapp et al., 1997; Ito et al., 2004; Kam et al., 1995). More recently, acquisition of resistance to highly effective cephalosporin agents (ceftriaxone and cefixime) has also been reported (Wang et al., 2003; Ito et al., 2004). Gonorrhoeae in individuals with a history of either foreign travel to areas of high QRNG prevalence or men who have sex with men has been recognized as risk factors for fluoroquinolone resistance, with recommendations to treat such individuals with either ceftriaxone or oral cefixime (CDC, 2002b).
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However, with the waxing and waning in the availability of cefixime, there is an urgent need for a safe, alternative highly effective ( N 95.0% cure rate; b 5.0% reported resistance) antigonococcal agent that can be administered orally, preferably with a single-dose regimen (CDC, 2002b). Our current study was performed to analyze the antigonococcal potency of gemifloxacin against a carefully selected sample of gonococcal isolates including contemporary strains (2004) from 6 sentinel sites in the United States where QRNG has occurred, enriched with isolates harboring established resistance phenotypes (PPNG, TRNG, CMRNG, and historic QRNG strains). Our results confirm that gemifloxacin continues to be most active in vitro among fluoroquinolones when tested against recent gonococcal isolates (MIC50 = 0.016 Ag/mL and MIC90 = 1 Ag/mL). Despite the preselection bias toward antimicrobial-resistant gonococcal isolates (entire collection QRNG rate of 38.8%, and high-level penicillin and tetracycline rates of 31.2% and 23.6%, respectively), the potency of gemifloxacin was competitive and positioned between that of ceftriaxone and older quinolones, penicillin, and tetracycline. Also corroborating the earlier reports (Jones et al., 2000a, 2000b), the activity of gemifloxacin was not affected by penicillinase production (PPNG), and the MIC90 value was 2-fold lower for penicillinase-positive when compared with the penicillinase-negative strains (0.5 versus 1 Ag/mL) (Berron et al., 2000; Jones et al., 2002a). Although the reported PPNG rates are more than 50.0% in certain countries of the southeast Asian and western Pacific regions, a decline in the PPNG rates has been noted recently in certain parts of the world including the United States (11.1% in 1991 to 1.0% in 2003) and Japan (7.9% in 1993–1994 to 2.0% in 1997–1998) (CDC, 2002b; Tanaka et al., 2000a; Tapsal et al., 2001; WHO, 2003). Investigators in Hong Kong, analyzing N. gonorrhoeae strains over a 2-year period (1992–1994), noted that the emergence of QRNG was associated with a rapid decline of rates of both PPNG and TRNG and attributed this decline to the bplasmid-curingQ effect of fluoroquinolones (Kam et al., 1995). However, increasing penicillin MIC was associated with z 8-fold increase in the MIC90 value of gemifloxacin and its comparators (ciprofloxacin, levofloxacin, ceftriaxone, and tetracycline), but the highest gemifloxacin MIC was only 2 Ag/mL. Occurrence of coresistance in gonococcal isolates resulting in increase in MIC values of structurally unrelated compounds such as h-lactams, tetracyclines, and fluoroquinolones has been reported previously (Tanaka et al., 2000a, 2000b, 2004; Dewi et al., 2004). It is recognized that coexistence of chromosomal mutations in the QRDR region contributing to fluoroquinolone resistance (gyrA with or without parC mutations) along with recognized chromosomal mutations in other loci like penA (decreased binding to PBP2), penB (reduced porin permeability conferring reduced susceptibility to penicillin, tetracycline, and quinolones), and mtr (multidrug efflux pump) can result in multidrug resistance in gonococcal isolates (Tanaka et al.,
2004). Testing 131 recent clinical N. gonorrhoeae isolates from Japan (72.5% QRNG), investigators noted that 71.0% of the strains carried mutations in both gyrA gene and mtrR coding sequence, substantiating the simultaneous occurrence of mutations in the QRDR regions and MtrRCDE efflux system (Dewi et al., 2004). Although cross-resistance among the various fluoroquinolones is well recognized, it is recommended that fluoroquinolones be analyzed independently due the differential target affinities (DNA gyrase and topoisomerase IV) of each compound, resulting in varying potencies (Berron et al., 2000; Jones et al., 2000a; Tanaka et al., 2000b). Although the MIC90 value of gemifloxacin was 128-fold higher for the ciprofloxacin-resistant compared with the ciprofloxacin-susceptible strains (2 versus 0.016 Ag/mL), the gemifloxacin MIC90 value was z 2-fold lower than that for the older quinolones analyzed for the QRNG strains. Analyzing 85 gonococcal isolates from Japan (20 with no mutations in QRDR region, 43 with mutations in gyrA alone, and 22 with mutations in both gyrA and parC regions), the investigators reported that gemifloxacin showed the strongest activity against all 3 subsets of strains compared with 6 other fluoroquinolones (ciprofloxacin, levofloxacin, norfloxacin, tosufloxacin, trovafloxacin, and sparfloxacin) (Tanaka et al., 2000b). Gemifloxacin retained potency against strains with a single gyrA mutation (MIC = 0.004– 0.06 Ag/mL) and those with 2 or 3 mutations within gyrA and parC (MIC = 0.03– 0.25 Ag/mL), and the superior activity was attributed to stronger inhibitory activity of GyrA and ParC proteins in comparison with the other quinolones (Morrissey and Tillotson, 2004; Tanaka et al., 2000b). It has also been reported that due to the bdualtargetingQ action of gemifloxacin, selection of resistant mutants during treatment would be less likely, and the anticipated incidence of spontaneous mutation was only 1 in 1012 to 1014 (File and Iannini, 2003; Ruiz et al., 2001). The 2 factors that are recognized to influence the antibiograms of gonococcal isolates are exposure time and geographic distribution (Tapsall, 2001). The resistance mechanism to quinolones in gonococci has been mainly due to chromosomal mutations in the target QRDR regions that develops incrementally, with stepwise accrual of chromosomal changes over a period resulting in gradual increase in the quinolone MIC (Tapsall, 2001). This observation was exemplified in the 50 historic QRNG strains isolated more than a decade ago in Japan and further analyzed in this study (Deguchi et al., 1995, 1996). These gonococci in which QRDR changes resulting in quinolone resistance was demonstrated for the first time had predominantly intermediate-level susceptibility to ciprofloxacin (88.0%), and correspondingly, the majority of the strains had a single mutation in gyrA (19/29 strains with QRDR changes, 65.5%) (Deguchi et al., 1996). This was in contrast to the 200 contemporary strains from 2004 analyzed in this study, where 93.6% (47/200 strains) of the QRNG strains were fully resistant to ciprofloxacin. This
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shift in the degree of reduced susceptibility to ciprofloxacin, resulted in a corresponding 4-fold increase in the MIC90 value of gemifloxacin over 10 years (1 versus 0.25 Ag/mL; Tables 2 and 3). The impact of the geographical distribution on the endemic antimicrobial susceptibility rates of gonococci recognized by the surveillance studies conducted worldwide and in United States was also evident from the 6 sentinel sites (states) in United States cited here (CDC, 2004a, 2004b; Tapsall et al., 2001; WHO, 2003). The ciprofloxacin resistance (MIC z 1 Ag/mL) rates for the states on the Pacific Coast (California, Oregon, and Washington) and Hawaii were very elevated, ranging from 13.3% (Oregon) to z 32.9% (Washington and Hawaii). These findings are in accord with the surveillance report from the Gonococcal Isolate Surveillance Project, where testing of 6,552 gonococcal isolates from 30 participating cities across the United States in 2003 found a staggering two thirds (186 strains) of the 4.1% isolates (270 total) resistant to ciprofloxacin were from California (CDC, 2004a). Similarly, an increase in the proportion of isolates resistant to ciprofloxacin among Gonococcal Isolate Surveillance Project isolates was also noted in Seattle (6.9% in 2003 versus 3.0% in 2002) and in Honolulu (13.3% in 2003 versus 11.7% in 2002) (CDC, 2004a). Irrespective of the high rates of ciprofloxacin resistance in our study, gemifloxacin remained most active against these strains (MIC90 V 0.008–1 Ag/mL). In contrast, to the high QRNG rates noted in the western states, the bacteremic isolates (24 strains) were exquisitely susceptible to the quinolones analyzed (ciprofloxacin, levofloxacin, and gemifloxacin MIC 90 V 0.03 Ag/mL) and ceftriaxone (MIC90 0.06 Ag/mL). This finding substantiates the report that a majority of the QRNG isolates are proline-requiring autotypes compared with bacteremic strains, which require arginine-hypoxanthine–uracil (Tanaka et al., 2004). In conclusion, our results confirm the high activity of gemifloxacin in comparison to the other fluoroquinolones analyzed against the collection of contemporary strains of N. gonorrhoeae, irrespective of the resistance mechanism or phenotype. Gemifloxacin with its documented potency, should be considered for further development as an antigonococcal agent to treat emerging strains that are resistant to penicillins, tetracycline, and some older fluoroquinolones or have become less responsive to azithromycin (Yong et al., 1997). Gemifloxacin concentrations in genitourinary tract tissues (KG Naber, Oscient Pharmaceuticals Report, data on file, 2005) indicates the following levels after a 320-mg dose: plasma C max (1.25 Ag/mL), ejaculate (1.4 – 8.0 Ag/mL; z 3 plasma concentration), prostatic fluid (0.119–3.12 Ag/mL), and vaginal secretions (15% of plasma concentration). The urinary excretion was 28% (elimination half-life, 25 h) compared with 81% for the ofloxacin control. Single-dose or short-course gemifloxacin regimens should be evaluated as dictated by pharmacokinetic/pharmacodynamic modeling.
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Acknowledgments The coauthors express their gratitude to the following contributors to this investigation: L Deshpande, DJ Biedenbach, MG Stilwell, and KL Meyer. We also thank Joseph DiPersio (Summa Health Systems), Dwight Hardy (University of Rochester Medical Center), Judy Fusco (TPMG Regional Laboratory— San Francisco), Sue Swanzy (University of Washington), and William Whittington (Hartonview Medical Center) for their assistance in the collection of recent clinical isolates. This study was sponsored by an educational/research grant by Replidyne, Inc. References Appelbaum PC, Hunter PA (2000) The fluoroquinolone antibacterials: past, present and future perspectives. Int J Antimicrob Agents 16:5 – 15. Appelbaum PC, Gillespie SH, Burley CJ, Tillotson GS (2004) Antimicrobial selection for community-acquired lower respiratory tract infections in the 21st century: a review of gemifloxacin. Int J Antimicrob Agents 23:533 – 546. Berron S, Vazquez JA, Giminez MJ, de la Fuente L, Aguilar L (2000) In vitro susceptibilities of 400 Spanish isolates of Neisseria gonorrhoeae to gemifloxacin and 11 other antimicrobial agents. Antimicrob Agents Chemother 44:2543 – 2544. Centers for Disease Control and Prevention (2002a) Discontinuation of cefixime tablets—United States. MMWR Morb Mortal Wkly Rep 51:1052. Centers for Disease Control and Prevention (2002b) Sexually transmitted diseases treatment guidelines 2002. MMWR Morb Mortal Wkly Rep 51(RR-6):1 – 78. Centers for Disease Control and Prevention (2004a) Increases in fluoroquinolone-resistant Neisseria gonorrhoeae among men who have sex with men—United States, 2003, and revised recommendations for gonorrhoea treatment, 2004. MMWR Morb Mortal Wkly Rep 53:335 – 338. Centers for Disease Control and Prevention (2004b) Sexually Transmitted Disease Surveillance 2003 Supplement: Gonococcal Isolate Surveillance Project (GISP) Annual Report—2003. Atlanta (GA)7 US Department of Health and Human Services. Clinical and Laboratory Standards Institute (2005) Performance standards for antimicrobial susceptibility testing 15th Informational Supplement M100-S15. Wayne (PA)7 CLSI. Deguchi T, Yasuda M, Asano M, Tada K, Iwata H, Komeda H, Ezaki T, Saito I, Kawada Y (1995) DNA gyrase mutations in quinolone-resistant clinical isolates of Neisseria gonorrhoeae. Antimicrob Agents Chemother 39:561 – 563. Deguchi T, Yasuda M, Nakano M, Ozeki S, Ezaki T, Saito I, Kawada Y (1996) Quinolone-resistant Neisseria gonorrhoeae: correlation of alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV with antimicrobial susceptibility profiles. Antimicrob Agents Chemother 40:1020 – 1023. Dewi BE, Akira S, Hayashi H, Ba-Thein W (2004) High occurrence of simultaneous mutations in target enzymes and MtrRCDE efflux system in quinolone-resistant Neisseria gonorrhoeae. Sex Transm Dis 31: 353 – 359. Emmerson AM, Jones AM (2003) The quinolones: decades of development and use. J Antimicrob Chemother 51:13 – 20. File Jr TM, Iannini PB (2003) A profile of gemifloxacin, a new respiratory fluoroquinolone. Today’s Ther Trends 21:415 – 435. Ito M, Yasuda M, Yokoi S, Ito S, Takahashi Y, Ishihara S, Maeda S, Deguchi T (2004) Remarkable increase in central Japan in 2001–2002 of Neisseria gonorrhoeae isolates with decreased susceptibility to penicillin, tetracycline, oral cephalosporins, and fluoroquinolones. Antimicrob Agents Chemother 48:3185 – 3187.
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