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In vitro activity of various antimicrobial agents against Staphylococcus aureus isolates including fluoroquinolone- and oxacillin-resistant strains
517
DIAGN MICROBIOL INFECT DIS 1992;15:517-521
ANTIMICROBIAL SUSCEPTIBILITY STUDIES
In vitro Activity of Various Antimicrobial Agents Against Staphylococcus aureus Isolates Including Fluoroquinolone- and Oxacillin-Resistant Strains Kenneth E. Aldridge, Ronald N. Jones, Arthur L. Barry, and Michael S. Gelfand
To determine susceptibility to 31 old and new antimicrobials, 44 strains of Staphylococcus aureus, most resistant to oxacillin and ciprofloxacin and isolated in a community hospital, were tested in vitro. For the peptide/peptide-derivative compounds, with the exception of mersacidin, all strains were inhibited by <-2 t~g/ml. Minimum inhibitory concentration (MIC)9o values indicated mupirocin, teicoplanin, and MDL 62211 to be fourfold more active than vancomycin, ramoplanin, and decaplanin. For fluoroquinolones, ciprofloxacin-resistant S. aureus exhibited high-level cross-resistance to ofloxacin, norfloxacin, fleroxacin, enoxacin, and Ro 23-9424. WIN 57253, a new fluorinated naphthyridine, showed good activity
against these strains. Among the jS-lactams, the penem-derivatire compounds (imipenem, meropenem, FCE 22101, and HRE 664) had the greatest activity, although resistance to each compound was detected among oxacillin-resistant S. aureus. The presence of tazobactam reduced the piperacillin MICgo fourfold. Oxacillin-susceptible strains were susceptible to cephalosporins/cephamycins, whereas most oxacillin-resistant strains exhibited resistance. This study has shown that certain old and new quinolones and peptide-derivative compounds have good in vitro activity against multiply resistant strains of S. aureus.
INTRODUCTION
of choice for t r e a t m e n t of these infections, the fluoroquinolone g r o u p of antibiotics has b e e n rep o r t e d to have g o o d in vitro activity against oxacillin-resistant a n d oxacillin-susceptible staphylococci (Aldridge et al., 1985; Smith a n d Eng, 1985). H o w e v e r , selection of fluoroquinolone-resistant ORSA m u t a n t s in the p r e s e n c e of subinhibitory concentrations of fluoroquinolones has b e e n rep o r t e d (Kayser a n d Novak, 1987). Moreover, in early therapeutic trials of fluoroquinolones for ORSA infections, small n u m b e r s of therapeutic failures w e r e associated with the d e v e l o p m e n t of resistant strains (Piercy et al., 1989; Smith et al., 1989). Currently within the United States, significant increases in f l u o r o q u i n o l o n e resistance a m o n g ORSA have b e e n r e p o r t e d within 12-18 m o n t h s after introduction of ciprofloxacin into use (Daum et al., 1990; Isaacs et al., 1988; Peterson et al., 1990;
Oxacillin-resistant Staphylococcus aureus (ORSA) is an i m p o r t a n t cause of hospital- a n d c o m m u n i t y acquired infections w o r l d w i d e (Brumfitt a n d H a m ilton-MiUer, 1989). Although vancomycin is the drug From the Louisiana State University Medical Center (K.E.A.), New Orleans, Louisiana; Clinical Microbiology Institute (R.N.J., A.L.B.), Tualatin, Oregon; and Methodist Hospital of Memphis (M.S.G.), Memphis, Tennessee, USA. Address reprint requests to Dr. K.E. Aldridge, Department of Medicine, LSU Medical Center, 1542 Tulane Avenue, New Orleans, LA 70112, USA. R. N. Jones is now at the Department of Pathology, University of Iowa College of Medicine, Iowa City, IA 52242, USA. Received 26 June 1991; revised and accepted 24 November 1991. © 1992 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5.00
518
Raviglione et al., 1990; Smith et al., 1990). The present study compares the in vitro activity of various old and new antimicrobials against S. aureus strains isolated during an endemic outbreak of ciprofloxacin-resistant ORSA infections in a community institution, the Methodist Hospital of Memphis.
MATERIALS A N D M E T H O D S Organisms The tests involved 44 nonduplicate strains of S. aureus isolated from respiratory, skin and skin structure, and urinary specimens. The isolates were collected randomly in 1988 from infected patients at the Methodist Hospital of Memphis during a period of increased ciprofloxacin resistance among oxacillinresistant S. aureus. All organisms were isolated from different infections and phage typing indicated multiple phage types. Among the 44 strains, 37 were oxacillin resistant and seven strains were oxacillin susceptible; 31 were ciprofloxacin resistant and 13 were ciprofloxacin susceptible; and 30 strains were ~3-1actamase producers. Oxacillin resistance was confirmed by growth on agar medium containing 4 p,g/ml of oxacillin and growth in 2% NaC1 broth medium containing 2 ~g/ml of oxacillin (Thornsberry and McDougal, 1983). f3-1actamase production was determined using the chromogenic cephalosporin test (Cefinase, Becton-Dickinson Mirobiology Systems, Cockeysville, MD) after each isolate was exposed to oxacillin to ensure f3-1actamase induction. All strains were coagulase positive.
Antimicrobials Each of the following antimicrobial agents was kindly provided by the manufacturer: decaplanin, mersacidin, cefotaxime, cefodizime, HRE 664, and HR-916 (Hoechst-Roussel, Somerville, NJ); teicoplanin, ramoplanin, and MDL 62211 (Merrell-Dow, Cincinnati, OH); vancomycin, cephalothin, cephalexin, and cefaclor (Eli Lilly, Indianapolis, IN); piperacillin, tazobactam, and cefixime (Lederle, Pearl River, NY); norfloxacin and imipenem (Merck Sharp & Dohme, West Point, PA); ciprofloxacin (Miles, West Haven, CT); ofloxacin (Ortho, Raritan, NJ): fleroxacin and Ro 23-9424 (Roche, Nutley, NJ); enoxacin (WarnerLambert, Detroit, MI); mupirocin (Smith Kline Beecham, Philadelphia, PA); WIN 57273 (SterlingWinthrop, Rensselaer, NY); cefuroxime and ceftazidime (Glaxo, Research Triangle Park, NC); cefotetan and meropenem (Stuart, Wilmington, DE); cefadroxil (Bristol, Evansville, IN); and FCE 22101 (Adria, Columbus, OH).
K.E. Aldridge et al.
TABLE 1 Comparison of Glycopeptide, Lipoglycopeptide, and Peptide Antimicrobials Against 44 Strains of Staphylococcus aureus
MIC (p,g/ml) Values Route/ Antimicrobial
Range
MIC50
MICg0
Parenteral Vancomycin Teicoplanin MDL 62211 Decaplanin Mersacidin-CSa Mersacidin-O b
0.5-1 0.12-1 0.12-0.5 0.5-2 4-16 8-32
0.5 0.12 0.12 1 8 16
1 0.25 0.25 1 8 32
Topical Mupirocin Ramoplanin
0.12-0.25 0.12-2
0.12 0.5
0.25 1
aTest medium supplemented with calciumions. bTest medium without calciumsupplementation. MIC, minimuminhibitoryconcentration.
Antimicrobial Susceptibility Testing Serial twofold dilutions of each antimicrobial agent were prepared in Mueller-Hinton broth supplemented with calcium and magnesium as recommended by the National Committee for Clinical Laboratory Standards (NCCLS, 1988). The dilution scheme for each antimicrobial agent was within a range of 0.06-256 ~g/ml in a total volume of 100 p~l per microdilution well. Piperacillin was combined with tazobactam in an 8:1 ratio. The inoculum of each isolate was prepared from a 18 to 24-hr agar plate by suspending growth in Mueller-Hinton broth equivalent to the density of a 0.5 McFarland nephelometer tube. The final inoculum size was 5 x 104 colony-forming units (CFU) per well (5 x 10s CFU/ml). All plates were incubated at 35°C in ambient air for 20-24 hr and read. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of each antimicrobial agent that inhibited the visible growth of the test isolate.
RESULTS A N D D I S C U S S I O N Table 1 shows the in vitro activity of the various peptide or peptide-derivative antimicrobials tested. With the exception of mersacidin, all the peptide class compounds showed excellent activity inhibiting all 44 strains at -<2 p,g/ml. MIC90 values showed mupirocin, teicoplanin, and MDL 62211 to be fourfold more active than vancomycin, ramoplanin, and decaplanin. O'Hare et al. (1988) have reported ramoplanin to be equally active against both oxacillinresistant and susceptible staphylococci. Neu and Neu
Susceptibility of Fluoroquinolone-Resistant ORSA
TABLE 2
Comparison of the in vitro Activity of Various Quinolones Against Ciprofloxacin-Resistant (Cipro-resist.) and Susceptible (Cipro-suscept.) Strains of Staphylococcus aureus
519
TABLE 3
Comparison of the in vitro Activity of Penem and Carbapenem Compounds and Piperacillin and Piperacillin/ Tazobactam Against Oxacillin-Resistant (Oxa-resist.) and Susceptible (Oxa-suscept.) Staphylococcus aureus
MIC (Ixg/ml) Values MIC (~g/ml) Values Antimicrobial
Range
MIC50
MICg0
No.
Antimicrobial
Strains
Range
>4 1
Imipenern Oxa-resist. Oxa-suscept.
37 7
<0.12->16 <0.06
0.25 <0.06
>16 <0.06
>8 0.25
>8 1
Meropenem Oxa-resist. Oxa-suscept.
37 7
0.12->64 <0.06--0.25
2 0.12
16 0.25
Ciprofloxacin a Cipro-resist. Cipro-suscept.
>4 0.25-2
>4 0.5
Ofloxacin Cipro-resist. Cipro-suscept.
>8 0.25-1
MIC50 MICg0
Norfloxacin Cipro-resist. Cipro-suscept.
>8 1->8
>8 2
>8 4
Enoxacin Cipro-resist. Cipro-suscept.
FCE 22101 Oxa-resist. Oxa-suscept.
37 7
0.12->64 0.12
1 0.12
4 0.12
>8 1->8
>8 2
>8 4
Fleroxacin Cipro-resist. Cipro-suscept.
HRE 664 Oxa-resist. Oxa-suscept.
37 7
0.12->64 0.06-0.12
1 <0.06
4 0.12
>8 0.5-2
>8 0.5
>8 1
Piperacillin 13-1actpos. 13-1actneg.
30 14
1-128 1-32
64 16
256 32
32 2
32 4
Pip/tazobactam 13-1actpos. 13-1actneg.
30 14
1-128 1-16
16 16
64 16
~<0.06 ~0.06
0.25 ~<0.06
Ro 23-9424 Cipro-resist. Cipro-suscept. WIN 57273 Cipro-resist. Cipro-suscept.
4->32 1-8 ~<0.06-0.25 ~<0.06
aResistance to ciprofloxacin was defined as >4 Ixg/ml (NCCLS, 1988); 31 strains were ciprofloxacin resistant and 13 strains were ciprofloxacin susceptible. MIC, minimum inhibitory concentration.
(1986) reported results similar to ours with ramoplanin, which included strains of ORSA. Dixson et al. (1988) have also shown that ramoplanin is more active than vancomycin against staphylococci, although as in our study they found mupirocin to be more active than vancomycin and ramoplanin. Moreover, Maple et al. (1989) reported after a worldwide sampling of ORSA that no resistance was detected to mupirocin (most active), ramoplanin, teicoplanin, or vancomycin. Although appreciably less active than other peptide agents, mersacidin in the presence of calcium ions was fourfold more active than when additional calcium was not present. Table 2 compares the activity of various fluorinated quinolones (or naphthyridine) and Ro 23-9424 (an esterified linkage of fleroxacin and desacetylcefotaxime) against the S. aureus strains. Ciprofloxacinresistant ORSA strains showed high level cross-resistance to other quinolones with the exception of WIN 57273. WIN 57273 was at least 32-fold to 256-
MIC, minimum inhibitory concentration.
fold more active than the other quinolones against these strains. For ciprofloxacin-susceptible ORSA strains, WIN 57273 was the most active compound tested with all MIC values -<0.06 txg/ml. Jones and Barry (1990) reported good activity for WIN 57273 against oxacillin-resistant and susceptible strains of S. aureus; however, they did not test fluoroquinolone-resistant strains. Sedlock et al. (1990) reported the superior activity of WIN 57273 over ciprofloxacin, ofloxacin, and amifloxacin against oxacillin-resistant and susceptible strains, including three ciprofloxacin-resistant strains. Kaatz and Seo (1990) reported good activity of WIN 57273 against oxacillin-susceptible and resistant strains selected in vitro for diminished susceptibility to ciprofloxacin and WIN 57273. Gu and Neu (1990) reported similar antistaphylococcal activity of Ro 23-9424, but no fluoroquinolone-resistant strains were tested. They also indicated that the activity of fleroxacin alone was better than that of the fleroxacinYdesacetylcefotaxime combination (Ro 23-9424) against oxacillin-susceptible S. aureus. Table 3 compares the activity of piperacillin and penem-class compounds against the 44 test strains. Among the penem class compounds tested, some
K.E. Aldridge et al.
520
TABLE 4
Comparison of the in vitro Activity of Various Cephalosporin/Cephamycin Antimicrobials Against OxacillinResistant (Oxa-resist.) and Susceptible (Oxa-suscept.) Staphylococcus aureus MIC (~g/ml) Values No.
Antimicrobial
Strains
Range
MIC50
MICg0
Cephalothin Oxa-resist. Oxa-suscept.
37 7
0.5->64 <0.25
2 <0.25
16 <0.25
Cephalexin Oxa-resist. Oxa-suscept.
37 7
16->64 2-4
>64 4
>64 4
Cefadroxil Oxa-resist. Oxa-suscept.
37 7
16->128 >128 2-4 2
>128 4
Cefaclor Oxa-resist. Oxa-suscept.
37 7
4-64 1-4
32 2
64 4
Cefuroxime Oxa-resist. Oxa-suscept.
37 7
4-64 1-4
32 2
64 4
Cefixime Oxa-resist. Oxa-suscept.
37 7
>64 8->16
>64 8
>64 >16
Cefotetan Oxa-resist. Oxa-suscept.
37 7
16->128 4-8
32 4
>128 8
Ceftazidime Oxa-resist. Oxa-suscept.
37 7
4->32 4-8
32 4
32 8
Cefotaxime Oxa-resist. Oxa-suscept.
37 7
4->64 4
16 4
>64 4
Cefodizime Oxa-resist. Oxa-suscept.
37 7
8->128 2-4
32 4
>128 4
HR-916 Oxa-resist. Oxa-suscept.
37 7
2->64 0.5-1
8 0.5
32 1
MIC, minimum inhibitory concentration.
resistant strains were detected to all four compounds and were restricted to oxacillin-resistant strains regardless of ciprofloxacin susceptibility. Of the ORSA strains, 89% were susceptible to imipenem and meropenem, 95% were susceptible to HRE 664, and 92%
susceptible to FCE 22101 at a concentration of 8 p~g/ml. Bauernfeind et al. (1989) reported findings similar to ours in that HRE 664 is more active than imipenem or meropenem against ORSA. Hobart (1989) has also reported that FCE 22101 is more active than imipenem against ORSA as has Piddock et al. (1989). The addition of tazobactam enhanced the activity of piperacillin against the test strains. Against the 30 f~lactamase producing strains, only 15% of the strains had piperacillin MIC values -<16 ~g/ml. In the presence of tazobactam, however, 73% of the same strains had MIC values -<16 p,g/ml. As expected, the cephalosporin/cephamycin compounds (Table 4) exhibited good activity against oxacillin-susceptible S. aureus, but poor activity against ORSA regardless of ciprofloxacin susceptibility. Two exceptions are cephalothin and HR-916. In the case of cephalothin, 92% of the ORSA isolates had MIC values -<16 p~g/ml, whereas for HR-916, 86% of the same isolates were inhibited at ---16 ~g/ml. However, this activity may be more apparent than real as we did not determine whether a small heteroresistant population was present among the test strains to these two compounds. In this study, we examined the susceptibility of strains of S. aureus based on their resistance to oxacillin and ciprofloxacin and their ability to produce ~-lactamase. Overall, the peptide/peptide-derivative antimicrobials were the most active regardless of resistance to oxacillin or ciprofloxacin. Among ciprofloxacin-resistant S. aureus, high-level cross-resistance was documented to other fluoroquinolones with the exception of WIN 57273, which had good activity against both cirpofloxacin-susceptible and resistant strains. Among ~-lactam compounds, the penems and carbapenems were the most active, although some resistant strains were noted for all four compounds. The presence of the [3-1actamase inhibitor tazobactam potentiated the activity of piperacillin against ~-lactamase-producing S. aureus strains; however, this reduction may not represent therapeutically achievable concentrations with regard to ORSA infections. For cephalosporin/cephamycin compounds, strains of ORSA were highly resistant, whereas oxacillin-susceptible strains were appreciably more susceptible. These results warrant further study of the newer compounds, particularly in vivo, against staphylococcal infections. Furthermore, as S. aureus, especially multiple resistant strains, continues to be a formidable therapeutic challenge in infectious disease additional susceptibility screening studies such as presented here will be needed to ensure the most effective choice of antimicrobial therapy in the clinical setting.
Susceptibility of Fluoroquinolone-Resistant ORSA
521
REFERENCES Aldridge KE, Janney A, Sanders CV (1985) Comparison of the activities of coumermycin, ciprofloxacin, teicoplanin, and other non-f~-lactam antibiotics against clinical isolates of methicillin-resistant Staphylococcus aureus from various geographical locations. Antimicrob Agents Chemother 28:634-638. Barry AL, Jones RN (1984) Cross-resistance among cinoxacin, ciprofloxacin, DJ-6783, enoxacin, nalidixic acid, norfloxacin, and oxolinic acid after in vitro selection of resistant populations. Antimicrob Agents Chemother25:775-777. Bauernfeind A, Jungwirth R, Schweighart S (1989) In vitro activity of ramoplanin (A-16686/MDL 62,198), vancomycin and teicoplanin against methicillin-susceptible and methicillin-resistant Staphylococcus spp. Drugs Exp Clin Res 14:617-619. Brumfitt W, Hamilton-Miller J (1989) Methicillin-resistant Staphylococcus aureus. N Engl J Med 320:1188-1196. Daum TE, Schaberg DR, Terpenning MS, Sottile WS, Kaufmann CA (1990) Increasing resistance of Staphylococcus aureus to ciprofloxacin. Antimicrob Agents Chemother 34:1862-1863. Dixson S, Brumfitt W, Hamilton-Miller JMT (1988) In vitro evaluation of ramoplanin (MDL 62198, A 16686). Eur 1 Clin Microbiol Infect Dis 1:819-821. Gu JW, Neu HC (1990) In vitro activity of Ro 23-9424, a dual-action cephalosporin, compared with activities of other antibiotics. Antimicrob Agents Chemother 34:189195. Hoban DJ (1989) In-vitro activity of a new penem FCE 22101. ] Antimicrob Chemother 23(Suppl C):53-57. Isaacs RD, Kunke PJ, Cohen RL, Smith JW (1988) Cirpofloxacin resistance in epidemic methicillin-resistant Staphylococcus aureus. Lancet 2:843. Jones RN, Barry AL (1990) In vitro evaluation of WIN 57273, a new broad-spectrum fluoroquinolone. Antimicrob Agents Chemother 34:306-313. Jones RN, Barry AL, Thornsberry C (1989) Antimicrobial activity of Ro 23-9424, a novel ester-linked co-drug of fleroxacin and desacetylcefotaxime. Antimicrob Agents Chemother 33:944-950. Kaatz GW, Seo SM (1990) WIN 57273, a new fluoroquinolone with enhanced in vitro activity versus Gram-positive pathogens. Antimicrob Agents Chemother 34:13761380. Kayser FH, Novak J (1987) In vitro activity of ciprofloxacin against Gram-positive bacteria: an overview. Am J Med 82(Suppl 4A):33--39. Maple PA, Hamilton-Miller JMT, Brumfitt W (1989) World-
wide antibiotic resistance in methicillin-resistant Staphylococcus aureus. Lancet 1:537-540. National Committee for Clinical Laboratory Standards (NCCLS) (1988) Standard M7-T2: methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Villanova, PA: NCCLS. Neu HC, Neu NM (1986). In vitro activity of A-16686, a new glycopeptide. Chemotherapy 32:453--457. O'Hare MD, Felmingham D, Grfineberg RN (1988) The in vitro activity of ramoplanin (A-16686/MDL 62,198), vancomycin and teicoplanin against methicillin-suscepfible and methicillin-resistant Staphylococcus spp. Drugs Exp Clin Res 14:617-619. Peterson LR, Quick JN, Jensen B, Homann S, Johnson S, Tenquist J, Shanholter C, Petzel RA, Sinn L, Gerding DN (1990) Emergence of ciprofloxacin resistance in nosocomial methicillin-resistant Staphylococus aureus isolates: resistance during ciprofloxacin plus rifampin therapy for methicillin-resistant S. aureus colonization. Arch Intern Med 150:2151-2155. Piddock LJV, Traynor EA, Wise R (1989) Activity of FCE 22101 against methicillin-resistant Staphylococcus aureus and affinity for penicillin binding proteins. ] Antimicrob Chemother 23(Suppl c):59-64. Piercy EA, Barbaras D, Luby JP, Mackowiak PA (1989) Ciprofloxacin for methiciUin-resistant Staphylococcus aureus infections. Antimicrob Agents Chemother 33:128-130. Raviglione MC, Boyle JF, Mauriz P, Pablos-Mendez A, Cortez H, Merlo A (1990) Cirpofloxacin-resistant methicillin-resistant Staphylococcus aureus in an acute care hospital. Antimicrob Agents Chemother 34:2050-2054. Sedlock DM, Dobson RA, Deuel DM, Lesher GY, Rake JB (1990) In vitro and in vivo activities of a new quinolone, WIN 57273, possessing potent activity against Grampositive bacteria. Antimicrob Agents Chemother 34:568575. Smith SM, Eng RHK (1985) Activity of ciprofloxacin against Staphylococcus aureus. Antimicrob Agents Chemother 27:688691. Smith SM, Eng RHK, Tecson-Tumang F (1989) Ciprofloxacin therapy for methicillin-resistant Staphylococcus aureus infections or colonizations. Antimicrob Agents Chemother 33:181-184. Smith SM, Eng RHK, Bais P, Fan-Harvard P, Tecson-Tumang F (1990) Epidemiology of ciprofloxacin resistance among patients with methicillin-resistant Staphylococcus aureus. J Antimicrob Chemother 26:567-572. Thornsberry C, McDougal LK (1983) Successful use of broth microdilution in susceptibility tests for methicillin-resistant (heteroresistant) staphylococci. J Clin Microbiol 18:1084-1091.
DIAGN MICROBIOL INFECT DIS 1992;15:517-521
ANTIMICROBIAL SUSCEPTIBILITY STUDIES
In vitro Activity of Various Antimicrobial Agents Against Staphylococcus aureus Isolates Including Fluoroquinolone- and Oxacillin-Resistant Strains Kenneth E. Aldridge, Ronald N. Jones, Arthur L. Barry, and Michael S. Gelfand
To determine susceptibility to 31 old and new antimicrobials, 44 strains of Staphylococcus aureus, most resistant to oxacillin and ciprofloxacin and isolated in a community hospital, were tested in vitro. For the peptide/peptide-derivative compounds, with the exception of mersacidin, all strains were inhibited by <-2 t~g/ml. Minimum inhibitory concentration (MIC)9o values indicated mupirocin, teicoplanin, and MDL 62211 to be fourfold more active than vancomycin, ramoplanin, and decaplanin. For fluoroquinolones, ciprofloxacin-resistant S. aureus exhibited high-level cross-resistance to ofloxacin, norfloxacin, fleroxacin, enoxacin, and Ro 23-9424. WIN 57253, a new fluorinated naphthyridine, showed good activity
against these strains. Among the jS-lactams, the penem-derivatire compounds (imipenem, meropenem, FCE 22101, and HRE 664) had the greatest activity, although resistance to each compound was detected among oxacillin-resistant S. aureus. The presence of tazobactam reduced the piperacillin MICgo fourfold. Oxacillin-susceptible strains were susceptible to cephalosporins/cephamycins, whereas most oxacillin-resistant strains exhibited resistance. This study has shown that certain old and new quinolones and peptide-derivative compounds have good in vitro activity against multiply resistant strains of S. aureus.
INTRODUCTION
of choice for t r e a t m e n t of these infections, the fluoroquinolone g r o u p of antibiotics has b e e n rep o r t e d to have g o o d in vitro activity against oxacillin-resistant a n d oxacillin-susceptible staphylococci (Aldridge et al., 1985; Smith a n d Eng, 1985). H o w e v e r , selection of fluoroquinolone-resistant ORSA m u t a n t s in the p r e s e n c e of subinhibitory concentrations of fluoroquinolones has b e e n rep o r t e d (Kayser a n d Novak, 1987). Moreover, in early therapeutic trials of fluoroquinolones for ORSA infections, small n u m b e r s of therapeutic failures w e r e associated with the d e v e l o p m e n t of resistant strains (Piercy et al., 1989; Smith et al., 1989). Currently within the United States, significant increases in f l u o r o q u i n o l o n e resistance a m o n g ORSA have b e e n r e p o r t e d within 12-18 m o n t h s after introduction of ciprofloxacin into use (Daum et al., 1990; Isaacs et al., 1988; Peterson et al., 1990;
Oxacillin-resistant Staphylococcus aureus (ORSA) is an i m p o r t a n t cause of hospital- a n d c o m m u n i t y acquired infections w o r l d w i d e (Brumfitt a n d H a m ilton-MiUer, 1989). Although vancomycin is the drug From the Louisiana State University Medical Center (K.E.A.), New Orleans, Louisiana; Clinical Microbiology Institute (R.N.J., A.L.B.), Tualatin, Oregon; and Methodist Hospital of Memphis (M.S.G.), Memphis, Tennessee, USA. Address reprint requests to Dr. K.E. Aldridge, Department of Medicine, LSU Medical Center, 1542 Tulane Avenue, New Orleans, LA 70112, USA. R. N. Jones is now at the Department of Pathology, University of Iowa College of Medicine, Iowa City, IA 52242, USA. Received 26 June 1991; revised and accepted 24 November 1991. © 1992 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5.00
518
Raviglione et al., 1990; Smith et al., 1990). The present study compares the in vitro activity of various old and new antimicrobials against S. aureus strains isolated during an endemic outbreak of ciprofloxacin-resistant ORSA infections in a community institution, the Methodist Hospital of Memphis.
MATERIALS A N D M E T H O D S Organisms The tests involved 44 nonduplicate strains of S. aureus isolated from respiratory, skin and skin structure, and urinary specimens. The isolates were collected randomly in 1988 from infected patients at the Methodist Hospital of Memphis during a period of increased ciprofloxacin resistance among oxacillinresistant S. aureus. All organisms were isolated from different infections and phage typing indicated multiple phage types. Among the 44 strains, 37 were oxacillin resistant and seven strains were oxacillin susceptible; 31 were ciprofloxacin resistant and 13 were ciprofloxacin susceptible; and 30 strains were ~3-1actamase producers. Oxacillin resistance was confirmed by growth on agar medium containing 4 p,g/ml of oxacillin and growth in 2% NaC1 broth medium containing 2 ~g/ml of oxacillin (Thornsberry and McDougal, 1983). f3-1actamase production was determined using the chromogenic cephalosporin test (Cefinase, Becton-Dickinson Mirobiology Systems, Cockeysville, MD) after each isolate was exposed to oxacillin to ensure f3-1actamase induction. All strains were coagulase positive.
Antimicrobials Each of the following antimicrobial agents was kindly provided by the manufacturer: decaplanin, mersacidin, cefotaxime, cefodizime, HRE 664, and HR-916 (Hoechst-Roussel, Somerville, NJ); teicoplanin, ramoplanin, and MDL 62211 (Merrell-Dow, Cincinnati, OH); vancomycin, cephalothin, cephalexin, and cefaclor (Eli Lilly, Indianapolis, IN); piperacillin, tazobactam, and cefixime (Lederle, Pearl River, NY); norfloxacin and imipenem (Merck Sharp & Dohme, West Point, PA); ciprofloxacin (Miles, West Haven, CT); ofloxacin (Ortho, Raritan, NJ): fleroxacin and Ro 23-9424 (Roche, Nutley, NJ); enoxacin (WarnerLambert, Detroit, MI); mupirocin (Smith Kline Beecham, Philadelphia, PA); WIN 57273 (SterlingWinthrop, Rensselaer, NY); cefuroxime and ceftazidime (Glaxo, Research Triangle Park, NC); cefotetan and meropenem (Stuart, Wilmington, DE); cefadroxil (Bristol, Evansville, IN); and FCE 22101 (Adria, Columbus, OH).
K.E. Aldridge et al.
TABLE 1 Comparison of Glycopeptide, Lipoglycopeptide, and Peptide Antimicrobials Against 44 Strains of Staphylococcus aureus
MIC (p,g/ml) Values Route/ Antimicrobial
Range
MIC50
MICg0
Parenteral Vancomycin Teicoplanin MDL 62211 Decaplanin Mersacidin-CSa Mersacidin-O b
0.5-1 0.12-1 0.12-0.5 0.5-2 4-16 8-32
0.5 0.12 0.12 1 8 16
1 0.25 0.25 1 8 32
Topical Mupirocin Ramoplanin
0.12-0.25 0.12-2
0.12 0.5
0.25 1
aTest medium supplemented with calciumions. bTest medium without calciumsupplementation. MIC, minimuminhibitoryconcentration.
Antimicrobial Susceptibility Testing Serial twofold dilutions of each antimicrobial agent were prepared in Mueller-Hinton broth supplemented with calcium and magnesium as recommended by the National Committee for Clinical Laboratory Standards (NCCLS, 1988). The dilution scheme for each antimicrobial agent was within a range of 0.06-256 ~g/ml in a total volume of 100 p~l per microdilution well. Piperacillin was combined with tazobactam in an 8:1 ratio. The inoculum of each isolate was prepared from a 18 to 24-hr agar plate by suspending growth in Mueller-Hinton broth equivalent to the density of a 0.5 McFarland nephelometer tube. The final inoculum size was 5 x 104 colony-forming units (CFU) per well (5 x 10s CFU/ml). All plates were incubated at 35°C in ambient air for 20-24 hr and read. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of each antimicrobial agent that inhibited the visible growth of the test isolate.
RESULTS A N D D I S C U S S I O N Table 1 shows the in vitro activity of the various peptide or peptide-derivative antimicrobials tested. With the exception of mersacidin, all the peptide class compounds showed excellent activity inhibiting all 44 strains at -<2 p,g/ml. MIC90 values showed mupirocin, teicoplanin, and MDL 62211 to be fourfold more active than vancomycin, ramoplanin, and decaplanin. O'Hare et al. (1988) have reported ramoplanin to be equally active against both oxacillinresistant and susceptible staphylococci. Neu and Neu
Susceptibility of Fluoroquinolone-Resistant ORSA
TABLE 2
Comparison of the in vitro Activity of Various Quinolones Against Ciprofloxacin-Resistant (Cipro-resist.) and Susceptible (Cipro-suscept.) Strains of Staphylococcus aureus
519
TABLE 3
Comparison of the in vitro Activity of Penem and Carbapenem Compounds and Piperacillin and Piperacillin/ Tazobactam Against Oxacillin-Resistant (Oxa-resist.) and Susceptible (Oxa-suscept.) Staphylococcus aureus
MIC (Ixg/ml) Values MIC (~g/ml) Values Antimicrobial
Range
MIC50
MICg0
No.
Antimicrobial
Strains
Range
>4 1
Imipenern Oxa-resist. Oxa-suscept.
37 7
<0.12->16 <0.06
0.25 <0.06
>16 <0.06
>8 0.25
>8 1
Meropenem Oxa-resist. Oxa-suscept.
37 7
0.12->64 <0.06--0.25
2 0.12
16 0.25
Ciprofloxacin a Cipro-resist. Cipro-suscept.
>4 0.25-2
>4 0.5
Ofloxacin Cipro-resist. Cipro-suscept.
>8 0.25-1
MIC50 MICg0
Norfloxacin Cipro-resist. Cipro-suscept.
>8 1->8
>8 2
>8 4
Enoxacin Cipro-resist. Cipro-suscept.
FCE 22101 Oxa-resist. Oxa-suscept.
37 7
0.12->64 0.12
1 0.12
4 0.12
>8 1->8
>8 2
>8 4
Fleroxacin Cipro-resist. Cipro-suscept.
HRE 664 Oxa-resist. Oxa-suscept.
37 7
0.12->64 0.06-0.12
1 <0.06
4 0.12
>8 0.5-2
>8 0.5
>8 1
Piperacillin 13-1actpos. 13-1actneg.
30 14
1-128 1-32
64 16
256 32
32 2
32 4
Pip/tazobactam 13-1actpos. 13-1actneg.
30 14
1-128 1-16
16 16
64 16
~<0.06 ~0.06
0.25 ~<0.06
Ro 23-9424 Cipro-resist. Cipro-suscept. WIN 57273 Cipro-resist. Cipro-suscept.
4->32 1-8 ~<0.06-0.25 ~<0.06
aResistance to ciprofloxacin was defined as >4 Ixg/ml (NCCLS, 1988); 31 strains were ciprofloxacin resistant and 13 strains were ciprofloxacin susceptible. MIC, minimum inhibitory concentration.
(1986) reported results similar to ours with ramoplanin, which included strains of ORSA. Dixson et al. (1988) have also shown that ramoplanin is more active than vancomycin against staphylococci, although as in our study they found mupirocin to be more active than vancomycin and ramoplanin. Moreover, Maple et al. (1989) reported after a worldwide sampling of ORSA that no resistance was detected to mupirocin (most active), ramoplanin, teicoplanin, or vancomycin. Although appreciably less active than other peptide agents, mersacidin in the presence of calcium ions was fourfold more active than when additional calcium was not present. Table 2 compares the activity of various fluorinated quinolones (or naphthyridine) and Ro 23-9424 (an esterified linkage of fleroxacin and desacetylcefotaxime) against the S. aureus strains. Ciprofloxacinresistant ORSA strains showed high level cross-resistance to other quinolones with the exception of WIN 57273. WIN 57273 was at least 32-fold to 256-
MIC, minimum inhibitory concentration.
fold more active than the other quinolones against these strains. For ciprofloxacin-susceptible ORSA strains, WIN 57273 was the most active compound tested with all MIC values -<0.06 txg/ml. Jones and Barry (1990) reported good activity for WIN 57273 against oxacillin-resistant and susceptible strains of S. aureus; however, they did not test fluoroquinolone-resistant strains. Sedlock et al. (1990) reported the superior activity of WIN 57273 over ciprofloxacin, ofloxacin, and amifloxacin against oxacillin-resistant and susceptible strains, including three ciprofloxacin-resistant strains. Kaatz and Seo (1990) reported good activity of WIN 57273 against oxacillin-susceptible and resistant strains selected in vitro for diminished susceptibility to ciprofloxacin and WIN 57273. Gu and Neu (1990) reported similar antistaphylococcal activity of Ro 23-9424, but no fluoroquinolone-resistant strains were tested. They also indicated that the activity of fleroxacin alone was better than that of the fleroxacinYdesacetylcefotaxime combination (Ro 23-9424) against oxacillin-susceptible S. aureus. Table 3 compares the activity of piperacillin and penem-class compounds against the 44 test strains. Among the penem class compounds tested, some
K.E. Aldridge et al.
520
TABLE 4
Comparison of the in vitro Activity of Various Cephalosporin/Cephamycin Antimicrobials Against OxacillinResistant (Oxa-resist.) and Susceptible (Oxa-suscept.) Staphylococcus aureus MIC (~g/ml) Values No.
Antimicrobial
Strains
Range
MIC50
MICg0
Cephalothin Oxa-resist. Oxa-suscept.
37 7
0.5->64 <0.25
2 <0.25
16 <0.25
Cephalexin Oxa-resist. Oxa-suscept.
37 7
16->64 2-4
>64 4
>64 4
Cefadroxil Oxa-resist. Oxa-suscept.
37 7
16->128 >128 2-4 2
>128 4
Cefaclor Oxa-resist. Oxa-suscept.
37 7
4-64 1-4
32 2
64 4
Cefuroxime Oxa-resist. Oxa-suscept.
37 7
4-64 1-4
32 2
64 4
Cefixime Oxa-resist. Oxa-suscept.
37 7
>64 8->16
>64 8
>64 >16
Cefotetan Oxa-resist. Oxa-suscept.
37 7
16->128 4-8
32 4
>128 8
Ceftazidime Oxa-resist. Oxa-suscept.
37 7
4->32 4-8
32 4
32 8
Cefotaxime Oxa-resist. Oxa-suscept.
37 7
4->64 4
16 4
>64 4
Cefodizime Oxa-resist. Oxa-suscept.
37 7
8->128 2-4
32 4
>128 4
HR-916 Oxa-resist. Oxa-suscept.
37 7
2->64 0.5-1
8 0.5
32 1
MIC, minimum inhibitory concentration.
resistant strains were detected to all four compounds and were restricted to oxacillin-resistant strains regardless of ciprofloxacin susceptibility. Of the ORSA strains, 89% were susceptible to imipenem and meropenem, 95% were susceptible to HRE 664, and 92%
susceptible to FCE 22101 at a concentration of 8 p~g/ml. Bauernfeind et al. (1989) reported findings similar to ours in that HRE 664 is more active than imipenem or meropenem against ORSA. Hobart (1989) has also reported that FCE 22101 is more active than imipenem against ORSA as has Piddock et al. (1989). The addition of tazobactam enhanced the activity of piperacillin against the test strains. Against the 30 f~lactamase producing strains, only 15% of the strains had piperacillin MIC values -<16 ~g/ml. In the presence of tazobactam, however, 73% of the same strains had MIC values -<16 p,g/ml. As expected, the cephalosporin/cephamycin compounds (Table 4) exhibited good activity against oxacillin-susceptible S. aureus, but poor activity against ORSA regardless of ciprofloxacin susceptibility. Two exceptions are cephalothin and HR-916. In the case of cephalothin, 92% of the ORSA isolates had MIC values -<16 p~g/ml, whereas for HR-916, 86% of the same isolates were inhibited at ---16 ~g/ml. However, this activity may be more apparent than real as we did not determine whether a small heteroresistant population was present among the test strains to these two compounds. In this study, we examined the susceptibility of strains of S. aureus based on their resistance to oxacillin and ciprofloxacin and their ability to produce ~-lactamase. Overall, the peptide/peptide-derivative antimicrobials were the most active regardless of resistance to oxacillin or ciprofloxacin. Among ciprofloxacin-resistant S. aureus, high-level cross-resistance was documented to other fluoroquinolones with the exception of WIN 57273, which had good activity against both cirpofloxacin-susceptible and resistant strains. Among ~-lactam compounds, the penems and carbapenems were the most active, although some resistant strains were noted for all four compounds. The presence of the [3-1actamase inhibitor tazobactam potentiated the activity of piperacillin against ~-lactamase-producing S. aureus strains; however, this reduction may not represent therapeutically achievable concentrations with regard to ORSA infections. For cephalosporin/cephamycin compounds, strains of ORSA were highly resistant, whereas oxacillin-susceptible strains were appreciably more susceptible. These results warrant further study of the newer compounds, particularly in vivo, against staphylococcal infections. Furthermore, as S. aureus, especially multiple resistant strains, continues to be a formidable therapeutic challenge in infectious disease additional susceptibility screening studies such as presented here will be needed to ensure the most effective choice of antimicrobial therapy in the clinical setting.
Susceptibility of Fluoroquinolone-Resistant ORSA
521
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