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Tigecycline in vitro activity against commonly encountered multidrug-resistant Gram-negative pathogens in a Middle Eastern country
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Diagnostic Microbiology and Infectious Disease 62 (2008) 411 – 415 www.elsevier.com/locate/diagmicrobio
Antimicrobial Susceptibility Studies
Tigecycline in vitro activity against commonly encountered multidrug-resistant Gram-negative pathogens in a Middle Eastern country George F. Araj⁎, Georges Y. Ibrahim Department of Pathology and Laboratory Medicine, American University of Beirut Medical Center, P.O. Box 116-3044, Beirut 11077-2020, Lebanon Received 20 March 2008; accepted 15 August 2008
Abstract The lack of data from the Middle East warranted studying tigecycline in vitro activity in Lebanon against consecutive multidrug-resistant (MDR) bacteria, including extended-spectrum β-lactamases producing clinical isolates of Escherichia coli (n = 150), Klebsiella pneumoniae (n = 100), and Acinetobacter spp. (n = 64) using the standard disk diffusion method. Tigecycline-resistant and intermediate findings were as follows: E. coli, 0% and 0%; K. pneumoniae, 3% and 16%; and Acinetobacter spp., 0% and 2%. These values were substantially lower than those determined for amikacin, gentamicin, tobramycin, ciprofloxacin, piperacillin/tazobactam, amoxicillin/clavulanic acid, and trimethoprim/sulfamethoxazole. This study demonstrates the excellent activity of tigecycline against the increasingly encountered MDR bacteria in Lebanon. The introduction of this effective and viable drug for the initial or recommended treatment of serious infections caused by such highly resistant pathogens is an asset for patients in this country and elsewhere. © 2008 Elsevier Inc. All rights reserved. Keywords: Tigecycline; Multidrug resistant; β-Lactamases; Surveillance
1. Introduction The effectiveness of existing antimicrobial agents such as β-lactams, β-lactam/β-lactamase inhibitors, aminoglycosides, fluoroquinolones, and trimethoprim/sulfamethoxazole has been seriously compromised because of the ever increasing prevalence of many multidrug-resistant (MDR) bacteria including the emergence of extended-spectrum β– lactamases (ESBLs) producing Escherichia coli and Klebsiella pneumoniae and Acinetobacter spp. strains all over the world (Li et al., 2007; Neuhauser et al., 2003; Perez et al., 2007; Samaha-Kfoury and Araj, 2003). The Middle Eastern countries including Lebanon have also been experiencing similar problems (Araj and Kanj, 2000; Kanafani et al., 2005; Samaha-Kfoury et al., 2005). Such serious situations reflected a dire need to develop alternative and more potent antimicrobial therapies, as exemplified by the introduction of tigecycline (Babinchak et al., 2005; Fraise 2006; Gales and
⁎ Corresponding author. Tel.: +961-3-628730; fax: +961-1-370845. E-mail address: [email protected] (G.F. Araj). 0732-8893/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2008.08.011
Jones, 2000; Livermore, 2005; Noskin, 2005; Schafer et al., 2007; Stein and Craig, 2006; Zinner, 2005). Primarily, the United States Food and Drug Administration approved tigecycline primarily for treating intraabdominal, skin, and skin structure complicated infections generally caused by a variety of MDR Gram-positive, Gram-negative (except Pseudomonas aeruginosa), and anaerobic bacteria. (Ellis-Grosse et al., 2005; Noskin, 2005; Wyeth Pharmaceuticals, 2005). The mechanisms and factors influencing or contributing to antimicrobial resistance are not uniform and may be specific to a particular country or region (Bouchillon et al., 2005). It is therefore warranted to study the in vitro activity of this new class of agents against isolates in a given location to assess their rate of resistance (Betriu et al., 2000; Bouchillon et al., 2005; Fritsche et al., 2005; Hoban et al., 2005; Reynolds et al., 2004; Tan and Ng, 2007). No data have been published on the activity of tigecycline in Lebanon and other Middle Eastern countries because this drug is still being under the process of introduction and registration. Thus, this study was undertaken to compare the in vitro activity of tigecycline versus
412
G.F. Araj, G.Y. Ibrahim / Diagnostic Microbiology and Infectious Disease 62 (2008) 411–415
other antimicrobial agents against the increasingly encountered MDR Acinetobacter spp. together with the ESBLproducing strains of E. coli and K. pneumoniae at a major tertiary care center in Lebanon.
according to the CLSI (2006). An organism was interpreted as containing an ESBL if there was an increase of ≥5 mm in the inhibition zone of the combination disk when compared with that of the cephalosporin alone. 2.4. Quality control
2. Materials and methods 2.1. Bacterial isolates A total of 314 consecutive clinically significant isolates of MDR isolates (resistant to several antimicrobial agents from at least 2 to 3 major classes such as β-lactams, fluoroquinolones, and aminoglycosides) and ESBL-producing E. coli (n = 150), K. pneumoniae (n = 100), and Acinetobacter spp. (n = 64) were recovered (between March 2006 and December 2007) from different specimens submitted to the clinical microbiology laboratory of the American University of Beirut Medical Center, the major tertiary care center in Lebanon. Only 1 isolate per patient was included, irrespective of the patient's medical history, antimicrobial use, age, or sex. Upon recovery from the clinical specimen source, all isolates were immediately identified based on standard methods (Murray et al., 2003) and tested against tigecycline and other antimicrobial agents. 2.2. Disk diffusion susceptibility testing The disk diffusion (DD) susceptibility testing was done using Mueller-Hinton agar (BD-BBL-Sparks, MD) according to the Clinical and Laboratory Standards Institute guidelines (CLSI, 2006). The antimicrobial disks (BDBBL) used and their concentrations were amikacin 30 μg, amoxicillin/clavulanate 20/10 μg, aztreonam 30 μg, cefepime 30 μg, cefixime 5 μg, cefotaxime 30 μg, cefoxitin 30 μg, ceftazidime 30 μg, ciprofloxacin 5 μg, gentamicin 10 μg, imipenem 10 μg piperacillin/tazobactam 100/10 μg, tobramycin 10 μg, trimethoprim/sulfamethoxazole 1.25/ 23.75 μg, and tigecycline 15 μg. The CLSI guidelines were also followed to interpret zone inhibition break points for all tested antimicrobials other than tigecycline. The interpretation of tigecycline break point inhibition zones (mm) for E. coli and K. pneumoniae was susceptible (S) ≥19, intermediate (I) = 15 to 18, and resistant (R) ≤14 (Wyeth Pharmaceuticals, 2005), and for Acinetobacter spp., were S ≥16 mm, I = 13 to 15 mm, R = ≤12 mm (Jones et al., 2007). 2.3. Suspicion and confirmation of ESBL production The ESBL-producing E. coli and K. pneumoniae isolates were suspected based on susceptibility to cefoxitin and imipenem and intermediate susceptibility or resistance to aztreonam, cefotaxime, and/or ceftazidime. The confirmation of ESBL presence was conducted by testing the following antibiotic disks: cefotaxime (30 μg), cefotaxime/ clavulanate (30/10 μg), ceftazidime (30 μg), and ceftazidime/clavulanate (30/10 μg) on Mueller–Hinton agar
The proper performance of the DD test method was ensured by using the American Type Culture Collection (ATCC) quality control strains E. coli (ATCC 25922) and P. aeruginosa (ATCC 27853). 3. Results 3.1. Patients demography and specimen source The patients' age ranged from ≤1 to ≥60 years. More E. coli were recovered from females than from males, whereas it was the reverse for K. pneumoniae and Acinetobacter spp. The most common specimen sources for the recovery of tested bacteria (with some variation among the species) were urine and respiratory and wound abscess, mostly originating from patients treated in the adult medical and surgical services. 3.2. Resistant and intermediate rates of tigecycline and other antimicrobials The resistant and intermediate resistant results for the tested antimicrobial agents are presented in Table 1. Compared with other study agents, tigecycline exhibited the lowest resistant results for all tested isolates. Among the E. coli strains, tigecycline exhibited activity equivalent to imipenem, and even 1 imipenem resistant strain was susceptible to tigecycline. Although imipenem maintained its potency against the K. pneumoniae isolates, tigecycline was slightly less active against this species group compared with the E. coli isolates. Among the Acinetobacter spp.., tigecycline was very active because none of the isolates showed resistance, and only a couple showed intermediate results. The remaining antimicrobial agents, with some exceptions to imipenem and amikacin, showed very high resistance rates to these isolates compared with tigecycline. In relation to the inhibition zone diameter, the majority of the isolates, especially E. coli and Acinetobacter spp., showed far larger inhibition zones than the specified susceptible interpretive break point zones: 92% of E. coli strains showed N22 mm, 80% of Acinetobacter spp.. showed N19 mm, and around 70% of K. pneumoniae showed N20 mm. 4. Discussion In Lebanon, as in other Middle Eastern countries, tigecycline is being under introduction and registration processing. The results of this 1st study from Lebanon
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413
Table 1 Results of in vitro activity of tigecycline versus other antimicrobial agents against MDR Gram-negative bacteria Antimicrobial agents
%a of findings among E. coli (n = 150)
Tigecycline Amikacin Aztreonamb Cefepimeb Ceftazidimeb Ciprofloxacinb Gentamicin Piperacillin/tazobactam Tobramycin Trimethoprim/sulfamethoxazole Imipenem Norfloxacin
K. pneumoniae (n = 100)
Acinetobacter spp. (n = 64)
R
I
S
R
I
S
R
I
S
0 2 82 51 54 77 50 7 65 77 0.5 76
0 5 12 21 25 3 2 32 5 0.5 0 2
100 93 6 28 21 20 48 61 30 22.5 99.5 22
3 19 92 53 82 46 51 19 70 62 0 47
16 14 6 20 10 4 2 47 4 3 0 4
81 67 2 27 8 50 47 34 26 35 100 49
0 53 76 40 66 67 57 42 52 60 30 29
2 8 16 29 2 3 5 27 0 0 5 29
98 39 8 31 32 30 38 31 48 40 65 42
a
The values were rounded off. Data for these antimicrobial agents are intended for Acinetobacter spp. and are not recommended for treatment of ESBL-producing E. coli and K. pneumoniae. b
demonstrate the high potency of this newly introduced antimicrobial agent against a broad range of MDR pathogens and are generally in agreement with studies reported from elsewhere (Betriu et al., 2000; Bouchillon et al., 2005; Fritsche et al., 2005; Hoban et al., 2005; Milatovic et al., 2003; Pachon-Ibanez et al., 2004; Reynolds et al., 2004; Sader et al., 2005; Tan and Ng, 2007; Waites et al., 2006; Zhang et al., 2004). For ESBL-producing E. coli, the present study demonstrated that tigecycline is universally effective without any resistance, similar finding to others (Biedenbach et al., 2001; Bouchillon et al., 2005; Tan and Ng, 2007; Waites et al., 2006). For ESBL-producing K. pneumoniae, the 3% resistance rates noted in the current study falls within the 0.1% to 6% resistant rates reported by others (Bouchillon et al., 2005; Sader et al., 2005; Tan and Ng, 2007). In relation to the distribution of inhibition zone diameter, 92% of E. coli strains showed N22 mm, and around 70% of K. pneumoniae showed N20 mm, that is, above the N19-mm specified susceptible break points for these bacteria (Wyeth Pharmaceuticals, 2005). For Acinetobacter spp., the absence of resistance strains to tigecycline in the current study favorably compared with the 0.9% to 9% resistant rates reported by others (Curcio and Fernandez, 2007; Fritsche et al., 2005; Reid et al., 2007; Sader et al., 2005; Tan and Ng, 2007; Tiengrim et al., 2006; Waites et al., 2006). Concerning the inhibition zone diameter, 80% of Acinetobacter spp. showed N19 mm, which is way above the N16-mm specified susceptible break point for these bacteria (Jones et al., 2007). For assessing novel compounds, MIC testing is recognized as the reference methodology, but we note that the DD methodology is also a valuable one, as recognized by CLSI. The possible limitation of DD in this study is that disk/MIC correlation has not yet been published for tigecycline (Sader HS et al. Re-evaluation of disk diffusion breakpoints for
tigecycline when testing Enterobacteriaceae. 107th American Society for Microbiology General Meeting, 2007, Abstract C-54). The excellent inhibitory activity of tigecycline observed against all resistance phenotypes of the tested pathogens in this study, regardless of the mechanisms of resistance involved, is consistent with the report from Biedenbach et al. (2001). Thus, ESBL activity in E. coli and K. pneumoniae had no or little effect on tigecycline activity (Table 1), similar to what was reported by Hoban et al. (2005). Compared with other drugs, tigecycline in vitro potency in this study was similar to imipenem for all MDR and ESBL-producing isolates of E. coli and K. pneumoniae (even 1 E. coli imipenem-resistant strain was susceptible to tigecycline) and showed higher activity against MDRproducing Acinetobacter spp. The in vitro potency of tigecycline was also higher than all the other classes of antimicrobial tested. Moreover, the potency of tigecycline seems to be independent of other antimicrobial agents. A recent in vitro study on the activity of tigecycline in combination with 16 antimicrobials against 32 Grampositive and 55 Gram-negative clinical isolates revealed primarily an indifferent effect (Vouillamoz et al., 2008). The lack of antagonism seen with tigecycline would suggest that this drug may prove to be effective in combination as well as in monotherapy. Granted such characteristics, tigecycline may provide an alternative treatment for infections caused by the presently tested isolates and other relevant bacteria showing resistance to β-lactams, fluoroquinolones, and other antimicrobial agents in different patient populations. Moreover, such an antimicrobial should help improve the morbidity and mortality rates, reduce healthcare costs, and potentially stave off resistance (Castanheira et al., 2008; Fraise, 2006). Like other antimicrobial agents, however, the inappropriate or overutilization of tigecycline will undoubtedly
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result in bacterial resistance. This potential risk was shown in the encountered intermediate (0–7%) and fully (2.9– 7.7%) resistant Acinetobacter baumannii strains recently reported from a couple of studies (Curcio and Fernandez, 2007; Reid et al., 2007). Therefore, it is important for infectious disease physicians and pharmacists to cautiously guide the prescription and use of this new antibiotics to safeguard and not undermine its excellent activity (Schafer et al., 2007). In conclusion, tigecycline exhibited high in vitro activity against most of the commonly encountered ESBL-producing and MDR bacterial pathogens in this country. Such findings reflect that tigecycline appears to be a promising new glycylcycline agent for the treatment of infections caused by numerous types of pathogens with varying resistance phenotypes detected in Lebanon and elsewhere. Acknowledgments The authors thank Hassan Beyh, Sohair Sabi, Lina Itani, Rania Hammoud, Nadia Ayyash, Aline Avedessian, Rima Asmar, and Maguy Malak for their excellent technical assistance. References Araj GF, Kanj SS (2000) Current status and changing trends of antimicrobial resistance in Lebanon. Leb Med J 48:221–226. Babinchak T, Ellis-Grosse E, Dartois N, Rose GM, Loh E (2005) The efficacy and safety of tigecycline for the treatment of complicated intraabdominal infections: analysis of pooled clinical trial data. Clin Infect Dis 41:S354–S367. Betriu C, Rodrı'guez-Avial L, Sánchez BA, Gómez M, Álvarez J, Picazo JJ, Spanish Group of Tigecycline (2000) In vitro activities of tigecycline (GAR-936) against recently isolated clinical bacteria in Spain. Antimicrob Agents Chemother 46:892–895. Biedenbach DJ, Beach ML, Jones RN (2001) In vitro antimicrobial activity of GAR-936 tested against antibiotic resistant gram-positive blood stream infection isolates and strains producing extended-spectrum βlactamases. Diagn Microbiol Infect Dis 40:173–177. Bouchillon SK, Hoban DJ, Johnson BM, Johnson JL, Hsiung A, Dowzicky MJ (2005) In vitro activity of tigecycline against 3989 Gram-negative and Gram-positive clinical isolates from the United States Tigecycline Evaluation and Surveillance Trial ( TEST Program; 2004). Diag Microbiol Infect Dis 52:173–179. Castanheira M, Sader HS, Deshpande LM, Fritsche TR, Jones RN (2008) Antimicrobial activity of tigecycline and other broad spectrum antimicrobials tested against serine carbapenemase- and metallo{beta}-lactamase–producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance program. Antimicrob Agents Chemother 52:570–573. Clinical and Laboratory Standards Institute (CLSI) (2006) Performance standards for antimicrobial susceptibility testing; sixteenth informational supplement, M100-S16. CLSI: Wayne (PA). Curcio D, Fernandez F (2007) Acinetobacter spp. Susceptibility to tigecycline: a worldwide perspective. J Antimicrob Chemother 60: 449–450. Ellis-Grosse EJ, Babinchak T, Dartois N, Rose G, Loh E (2005) The efficacy and safety of tigecycline in the treatment of skin and skin-structure infections: results of 2 double-blind phase 3 comparison studies with vancomycin–aztreonam. Clin Infect Dis 41:S341–S353.
Fraise AP (2006) Tigecycline: the answer to beta-lactam and fluoroquinolone resistance? J Infect 53:293–300. Fritsche TR, Sader HS, Stilwell MG, Dowzicky MJ, Jones RN (2005) Potency and spectrum of tigecycline tested against an international collection of bacterial pathogens associated with skin and soft tissue infections (2000–2004). Diagn Microbiol Infect Dis 52: 195–201. Gales AC, Jones RN (2000) Antimicrobial activity and spectrum of the new glycylcycline, GAR-936 tested against 1,203 recent clinical bacterial isolates. Diagn Microbiol Infect Dis 36:19–36. Hoban DJ, Bouchillon SK, Johnson BM, Johnson JL, Dowzicky MJ (2005) In vitro activity of tigecycline against 6792 Gram-negative and Grampositive clinical isolates from the global Tigecycline Evaluation and Surveillance Trial (TEST Program, 2004). Diagn Microbiol Infect Dis 52:215–227. Jones RN, Ferraro MJ, Reller LB, Schreckenberger PC, Swenson JM, Sader HS (2007) Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp. J Clin Microbiol 45:227–230. Kanafani ZA, Mehio-Sibai A, Araj GF, Kanaan M, Kanj SS (2005) Epidemiology and risk factors for extended-spectrum beta-lactamase producing organisms: a case control study at a tertiary care center in Lebanon. Am J Infect Control 33:326–332. Li J, Nation RL, Owen RJ, Wong S, Spelman D, Franklin C (2007) Antibiogram of multidrug-resistant clinical Acinetobacter baumannii: promising therapeutic options for treatment of infection with colistinresistant strains. CID 45:594–598. Livermore DM (2005) Tigecycline: what is it, and where should it be used? J Antimicrob Chemother 56:611–614. Milatovic D, Schmitz FJ, Verhoef J, Fluit AC (2003) Activities of the glycylcycline tigecycline (GAR-936) against 1,924 recent European clinical bacterial isolates. Antimicrob Agents Chemother 47: 400–404. Murray PR, Baron EJ, Jorgensen JH, Pfaller MA, Yolken RH (2003) Manual of Clinical Microbiology, 8th ed. American Society for Microbiology: Washington, DC. Neuhauser MM, Weinstein RA, Rydman R, Danziger LH, Karam G, Quinn JP (2003) Antibiotic resistance among Gram-negative bacilli in US intensive care units: implications for fluoroquinolone use. JAMA 289:885–888. Noskin GA (2005) Tigecycline; a new glyclycline for treatment of serious infections. CID 41:S303–S314. Pachon-Ibanez ME, Jimenez-Mejias ME, Pichardo C, Llaanos AC, Pachon J (2004) Activity of tigecycline (GAR-936) against Acinetobacter baumannii strains, including those resistant to imipenem. Antimicrob Agents Chemother 48:4479–4481. Perez F, Hujer AM, Hujer KM, Decker BK, Rather PN, Bonomo RA (2007) Global challenge of multidrug-resistant Acinetobacter baumannii. Antimicrob Agents Chemother 3471–3484. Reid GE, Grim SA, Aldeza CA, Janda WM, Clark NM (2007) Rapid development of Acinetobacter baumannii resistance to tigecycline. Pharmacotherapy 27:1198–1201. Reynolds R, Potz N, Colman M, Williams A, Livermore D, MacGowan A, on behalf of the BSAC Extended Working group on Bacteraemia Resistance Surveillance (2004) Antimicrobial susceptibility of the pathogens of bacteraemia in the UK and Ireland 2001–2002: the BSAC bacteraemia resistance surveillance programme. J Antimicrob Chemother 53:1018–1032. Sader HS, Jones RN, Stiwell MG, Dowzicky MJ, Fritsche TR (2005) Tigecycline activity tested against 26,474 bloodstream infection isolates: a collection from 6 continents. Diagn Microbiol Infect Dis 52:181–186. Schafer JJ, Goff DA, Stevenson KB, Mangino JE (2007) Early experience with tigecycline for ventilator-associated pneumonia and bacteremia caused by multidrug-resistant Acinetobacter baumannii. Pharmacotherapy 27:980–987. Samaha-Kfoury JN, Araj GF (2003) Recent developments in β-lactamases and extended spectrum β-lactamases. BMJ 327:1209–1213.
G.F. Araj, G.Y. Ibrahim / Diagnostic Microbiology and Infectious Disease 62 (2008) 411–415 Samaha-Kfoury J, Kanj SS, Araj GF (2005) In vitro activity of antimicrobial agents against extended-spectrum B-lactamase producing Escherichia coli and Klebsiella pneumoniae at a tertiary care center in Lebanon. Am J Infect Control 33:134–136. Stein GE, Craig WA (2006) Tigecycline: a critical analysis. CID 43:518–524. Tan TY, Ng LSY (2007) Susceptibility of multi-resistant gram-negative bacilli in Singapore to tigecycline as tested by agar dilution. Ann Acad Med Singapore 36:807–810. Tiengrim S, Tribuddharat C, Thamlikitkul V (2006) In vitro activity of tigecycline against clinical isolates of multidrug-resistant Acinetobacter baumannii in Siriraj Hospital, Thailand. J Med Assoc Thai 89(Suppl 5): S102–S105. Vouillamoz J Moreillon P, Giddey M, Entenza JM (2008) In vitro activities of tigecycline combined with other antimicrobials against multiresistant
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Gram-positive and Gram-negative pathogens. J Antimicrob Chemother 61:371–374. Waites KB, Duffy LB, Dowzicky MJ (2006) Antimicrobial susceptibility among pathogens collected from hospitalized patients in the United States and in vitro activity of tigecycline, a new glycylcycline antimicrobial. Antimicrob Agents Chemother 50: 3479–3484. Wyeth Pharmaceuticals (2005) Tigacil (tigecycline) product insert. Wyeth Pharmaceuticals: Philadelphia, PA. [online] http://www.tygacil.com. Zhang YY, Zhou L, Zhu DM, Wu PC, Hu FP, Wu WH, Wang F (2004) In vitro activities of tigecycline against clinical isolates from Shanghai, China. Diagn Microbiol Infect Dis 50:267–281. Zinner SH (2005) Overview of antibiotic use and resistance: setting the stage for tigecycline. CID 41:S289–S292.
Diagnostic Microbiology and Infectious Disease 62 (2008) 411 – 415 www.elsevier.com/locate/diagmicrobio
Antimicrobial Susceptibility Studies
Tigecycline in vitro activity against commonly encountered multidrug-resistant Gram-negative pathogens in a Middle Eastern country George F. Araj⁎, Georges Y. Ibrahim Department of Pathology and Laboratory Medicine, American University of Beirut Medical Center, P.O. Box 116-3044, Beirut 11077-2020, Lebanon Received 20 March 2008; accepted 15 August 2008
Abstract The lack of data from the Middle East warranted studying tigecycline in vitro activity in Lebanon against consecutive multidrug-resistant (MDR) bacteria, including extended-spectrum β-lactamases producing clinical isolates of Escherichia coli (n = 150), Klebsiella pneumoniae (n = 100), and Acinetobacter spp. (n = 64) using the standard disk diffusion method. Tigecycline-resistant and intermediate findings were as follows: E. coli, 0% and 0%; K. pneumoniae, 3% and 16%; and Acinetobacter spp., 0% and 2%. These values were substantially lower than those determined for amikacin, gentamicin, tobramycin, ciprofloxacin, piperacillin/tazobactam, amoxicillin/clavulanic acid, and trimethoprim/sulfamethoxazole. This study demonstrates the excellent activity of tigecycline against the increasingly encountered MDR bacteria in Lebanon. The introduction of this effective and viable drug for the initial or recommended treatment of serious infections caused by such highly resistant pathogens is an asset for patients in this country and elsewhere. © 2008 Elsevier Inc. All rights reserved. Keywords: Tigecycline; Multidrug resistant; β-Lactamases; Surveillance
1. Introduction The effectiveness of existing antimicrobial agents such as β-lactams, β-lactam/β-lactamase inhibitors, aminoglycosides, fluoroquinolones, and trimethoprim/sulfamethoxazole has been seriously compromised because of the ever increasing prevalence of many multidrug-resistant (MDR) bacteria including the emergence of extended-spectrum β– lactamases (ESBLs) producing Escherichia coli and Klebsiella pneumoniae and Acinetobacter spp. strains all over the world (Li et al., 2007; Neuhauser et al., 2003; Perez et al., 2007; Samaha-Kfoury and Araj, 2003). The Middle Eastern countries including Lebanon have also been experiencing similar problems (Araj and Kanj, 2000; Kanafani et al., 2005; Samaha-Kfoury et al., 2005). Such serious situations reflected a dire need to develop alternative and more potent antimicrobial therapies, as exemplified by the introduction of tigecycline (Babinchak et al., 2005; Fraise 2006; Gales and
⁎ Corresponding author. Tel.: +961-3-628730; fax: +961-1-370845. E-mail address: [email protected] (G.F. Araj). 0732-8893/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2008.08.011
Jones, 2000; Livermore, 2005; Noskin, 2005; Schafer et al., 2007; Stein and Craig, 2006; Zinner, 2005). Primarily, the United States Food and Drug Administration approved tigecycline primarily for treating intraabdominal, skin, and skin structure complicated infections generally caused by a variety of MDR Gram-positive, Gram-negative (except Pseudomonas aeruginosa), and anaerobic bacteria. (Ellis-Grosse et al., 2005; Noskin, 2005; Wyeth Pharmaceuticals, 2005). The mechanisms and factors influencing or contributing to antimicrobial resistance are not uniform and may be specific to a particular country or region (Bouchillon et al., 2005). It is therefore warranted to study the in vitro activity of this new class of agents against isolates in a given location to assess their rate of resistance (Betriu et al., 2000; Bouchillon et al., 2005; Fritsche et al., 2005; Hoban et al., 2005; Reynolds et al., 2004; Tan and Ng, 2007). No data have been published on the activity of tigecycline in Lebanon and other Middle Eastern countries because this drug is still being under the process of introduction and registration. Thus, this study was undertaken to compare the in vitro activity of tigecycline versus
412
G.F. Araj, G.Y. Ibrahim / Diagnostic Microbiology and Infectious Disease 62 (2008) 411–415
other antimicrobial agents against the increasingly encountered MDR Acinetobacter spp. together with the ESBLproducing strains of E. coli and K. pneumoniae at a major tertiary care center in Lebanon.
according to the CLSI (2006). An organism was interpreted as containing an ESBL if there was an increase of ≥5 mm in the inhibition zone of the combination disk when compared with that of the cephalosporin alone. 2.4. Quality control
2. Materials and methods 2.1. Bacterial isolates A total of 314 consecutive clinically significant isolates of MDR isolates (resistant to several antimicrobial agents from at least 2 to 3 major classes such as β-lactams, fluoroquinolones, and aminoglycosides) and ESBL-producing E. coli (n = 150), K. pneumoniae (n = 100), and Acinetobacter spp. (n = 64) were recovered (between March 2006 and December 2007) from different specimens submitted to the clinical microbiology laboratory of the American University of Beirut Medical Center, the major tertiary care center in Lebanon. Only 1 isolate per patient was included, irrespective of the patient's medical history, antimicrobial use, age, or sex. Upon recovery from the clinical specimen source, all isolates were immediately identified based on standard methods (Murray et al., 2003) and tested against tigecycline and other antimicrobial agents. 2.2. Disk diffusion susceptibility testing The disk diffusion (DD) susceptibility testing was done using Mueller-Hinton agar (BD-BBL-Sparks, MD) according to the Clinical and Laboratory Standards Institute guidelines (CLSI, 2006). The antimicrobial disks (BDBBL) used and their concentrations were amikacin 30 μg, amoxicillin/clavulanate 20/10 μg, aztreonam 30 μg, cefepime 30 μg, cefixime 5 μg, cefotaxime 30 μg, cefoxitin 30 μg, ceftazidime 30 μg, ciprofloxacin 5 μg, gentamicin 10 μg, imipenem 10 μg piperacillin/tazobactam 100/10 μg, tobramycin 10 μg, trimethoprim/sulfamethoxazole 1.25/ 23.75 μg, and tigecycline 15 μg. The CLSI guidelines were also followed to interpret zone inhibition break points for all tested antimicrobials other than tigecycline. The interpretation of tigecycline break point inhibition zones (mm) for E. coli and K. pneumoniae was susceptible (S) ≥19, intermediate (I) = 15 to 18, and resistant (R) ≤14 (Wyeth Pharmaceuticals, 2005), and for Acinetobacter spp., were S ≥16 mm, I = 13 to 15 mm, R = ≤12 mm (Jones et al., 2007). 2.3. Suspicion and confirmation of ESBL production The ESBL-producing E. coli and K. pneumoniae isolates were suspected based on susceptibility to cefoxitin and imipenem and intermediate susceptibility or resistance to aztreonam, cefotaxime, and/or ceftazidime. The confirmation of ESBL presence was conducted by testing the following antibiotic disks: cefotaxime (30 μg), cefotaxime/ clavulanate (30/10 μg), ceftazidime (30 μg), and ceftazidime/clavulanate (30/10 μg) on Mueller–Hinton agar
The proper performance of the DD test method was ensured by using the American Type Culture Collection (ATCC) quality control strains E. coli (ATCC 25922) and P. aeruginosa (ATCC 27853). 3. Results 3.1. Patients demography and specimen source The patients' age ranged from ≤1 to ≥60 years. More E. coli were recovered from females than from males, whereas it was the reverse for K. pneumoniae and Acinetobacter spp. The most common specimen sources for the recovery of tested bacteria (with some variation among the species) were urine and respiratory and wound abscess, mostly originating from patients treated in the adult medical and surgical services. 3.2. Resistant and intermediate rates of tigecycline and other antimicrobials The resistant and intermediate resistant results for the tested antimicrobial agents are presented in Table 1. Compared with other study agents, tigecycline exhibited the lowest resistant results for all tested isolates. Among the E. coli strains, tigecycline exhibited activity equivalent to imipenem, and even 1 imipenem resistant strain was susceptible to tigecycline. Although imipenem maintained its potency against the K. pneumoniae isolates, tigecycline was slightly less active against this species group compared with the E. coli isolates. Among the Acinetobacter spp.., tigecycline was very active because none of the isolates showed resistance, and only a couple showed intermediate results. The remaining antimicrobial agents, with some exceptions to imipenem and amikacin, showed very high resistance rates to these isolates compared with tigecycline. In relation to the inhibition zone diameter, the majority of the isolates, especially E. coli and Acinetobacter spp., showed far larger inhibition zones than the specified susceptible interpretive break point zones: 92% of E. coli strains showed N22 mm, 80% of Acinetobacter spp.. showed N19 mm, and around 70% of K. pneumoniae showed N20 mm. 4. Discussion In Lebanon, as in other Middle Eastern countries, tigecycline is being under introduction and registration processing. The results of this 1st study from Lebanon
G.F. Araj, G.Y. Ibrahim / Diagnostic Microbiology and Infectious Disease 62 (2008) 411–415
413
Table 1 Results of in vitro activity of tigecycline versus other antimicrobial agents against MDR Gram-negative bacteria Antimicrobial agents
%a of findings among E. coli (n = 150)
Tigecycline Amikacin Aztreonamb Cefepimeb Ceftazidimeb Ciprofloxacinb Gentamicin Piperacillin/tazobactam Tobramycin Trimethoprim/sulfamethoxazole Imipenem Norfloxacin
K. pneumoniae (n = 100)
Acinetobacter spp. (n = 64)
R
I
S
R
I
S
R
I
S
0 2 82 51 54 77 50 7 65 77 0.5 76
0 5 12 21 25 3 2 32 5 0.5 0 2
100 93 6 28 21 20 48 61 30 22.5 99.5 22
3 19 92 53 82 46 51 19 70 62 0 47
16 14 6 20 10 4 2 47 4 3 0 4
81 67 2 27 8 50 47 34 26 35 100 49
0 53 76 40 66 67 57 42 52 60 30 29
2 8 16 29 2 3 5 27 0 0 5 29
98 39 8 31 32 30 38 31 48 40 65 42
a
The values were rounded off. Data for these antimicrobial agents are intended for Acinetobacter spp. and are not recommended for treatment of ESBL-producing E. coli and K. pneumoniae. b
demonstrate the high potency of this newly introduced antimicrobial agent against a broad range of MDR pathogens and are generally in agreement with studies reported from elsewhere (Betriu et al., 2000; Bouchillon et al., 2005; Fritsche et al., 2005; Hoban et al., 2005; Milatovic et al., 2003; Pachon-Ibanez et al., 2004; Reynolds et al., 2004; Sader et al., 2005; Tan and Ng, 2007; Waites et al., 2006; Zhang et al., 2004). For ESBL-producing E. coli, the present study demonstrated that tigecycline is universally effective without any resistance, similar finding to others (Biedenbach et al., 2001; Bouchillon et al., 2005; Tan and Ng, 2007; Waites et al., 2006). For ESBL-producing K. pneumoniae, the 3% resistance rates noted in the current study falls within the 0.1% to 6% resistant rates reported by others (Bouchillon et al., 2005; Sader et al., 2005; Tan and Ng, 2007). In relation to the distribution of inhibition zone diameter, 92% of E. coli strains showed N22 mm, and around 70% of K. pneumoniae showed N20 mm, that is, above the N19-mm specified susceptible break points for these bacteria (Wyeth Pharmaceuticals, 2005). For Acinetobacter spp., the absence of resistance strains to tigecycline in the current study favorably compared with the 0.9% to 9% resistant rates reported by others (Curcio and Fernandez, 2007; Fritsche et al., 2005; Reid et al., 2007; Sader et al., 2005; Tan and Ng, 2007; Tiengrim et al., 2006; Waites et al., 2006). Concerning the inhibition zone diameter, 80% of Acinetobacter spp. showed N19 mm, which is way above the N16-mm specified susceptible break point for these bacteria (Jones et al., 2007). For assessing novel compounds, MIC testing is recognized as the reference methodology, but we note that the DD methodology is also a valuable one, as recognized by CLSI. The possible limitation of DD in this study is that disk/MIC correlation has not yet been published for tigecycline (Sader HS et al. Re-evaluation of disk diffusion breakpoints for
tigecycline when testing Enterobacteriaceae. 107th American Society for Microbiology General Meeting, 2007, Abstract C-54). The excellent inhibitory activity of tigecycline observed against all resistance phenotypes of the tested pathogens in this study, regardless of the mechanisms of resistance involved, is consistent with the report from Biedenbach et al. (2001). Thus, ESBL activity in E. coli and K. pneumoniae had no or little effect on tigecycline activity (Table 1), similar to what was reported by Hoban et al. (2005). Compared with other drugs, tigecycline in vitro potency in this study was similar to imipenem for all MDR and ESBL-producing isolates of E. coli and K. pneumoniae (even 1 E. coli imipenem-resistant strain was susceptible to tigecycline) and showed higher activity against MDRproducing Acinetobacter spp. The in vitro potency of tigecycline was also higher than all the other classes of antimicrobial tested. Moreover, the potency of tigecycline seems to be independent of other antimicrobial agents. A recent in vitro study on the activity of tigecycline in combination with 16 antimicrobials against 32 Grampositive and 55 Gram-negative clinical isolates revealed primarily an indifferent effect (Vouillamoz et al., 2008). The lack of antagonism seen with tigecycline would suggest that this drug may prove to be effective in combination as well as in monotherapy. Granted such characteristics, tigecycline may provide an alternative treatment for infections caused by the presently tested isolates and other relevant bacteria showing resistance to β-lactams, fluoroquinolones, and other antimicrobial agents in different patient populations. Moreover, such an antimicrobial should help improve the morbidity and mortality rates, reduce healthcare costs, and potentially stave off resistance (Castanheira et al., 2008; Fraise, 2006). Like other antimicrobial agents, however, the inappropriate or overutilization of tigecycline will undoubtedly
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result in bacterial resistance. This potential risk was shown in the encountered intermediate (0–7%) and fully (2.9– 7.7%) resistant Acinetobacter baumannii strains recently reported from a couple of studies (Curcio and Fernandez, 2007; Reid et al., 2007). Therefore, it is important for infectious disease physicians and pharmacists to cautiously guide the prescription and use of this new antibiotics to safeguard and not undermine its excellent activity (Schafer et al., 2007). In conclusion, tigecycline exhibited high in vitro activity against most of the commonly encountered ESBL-producing and MDR bacterial pathogens in this country. Such findings reflect that tigecycline appears to be a promising new glycylcycline agent for the treatment of infections caused by numerous types of pathogens with varying resistance phenotypes detected in Lebanon and elsewhere. Acknowledgments The authors thank Hassan Beyh, Sohair Sabi, Lina Itani, Rania Hammoud, Nadia Ayyash, Aline Avedessian, Rima Asmar, and Maguy Malak for their excellent technical assistance. References Araj GF, Kanj SS (2000) Current status and changing trends of antimicrobial resistance in Lebanon. Leb Med J 48:221–226. Babinchak T, Ellis-Grosse E, Dartois N, Rose GM, Loh E (2005) The efficacy and safety of tigecycline for the treatment of complicated intraabdominal infections: analysis of pooled clinical trial data. Clin Infect Dis 41:S354–S367. Betriu C, Rodrı'guez-Avial L, Sánchez BA, Gómez M, Álvarez J, Picazo JJ, Spanish Group of Tigecycline (2000) In vitro activities of tigecycline (GAR-936) against recently isolated clinical bacteria in Spain. Antimicrob Agents Chemother 46:892–895. Biedenbach DJ, Beach ML, Jones RN (2001) In vitro antimicrobial activity of GAR-936 tested against antibiotic resistant gram-positive blood stream infection isolates and strains producing extended-spectrum βlactamases. Diagn Microbiol Infect Dis 40:173–177. Bouchillon SK, Hoban DJ, Johnson BM, Johnson JL, Hsiung A, Dowzicky MJ (2005) In vitro activity of tigecycline against 3989 Gram-negative and Gram-positive clinical isolates from the United States Tigecycline Evaluation and Surveillance Trial ( TEST Program; 2004). Diag Microbiol Infect Dis 52:173–179. Castanheira M, Sader HS, Deshpande LM, Fritsche TR, Jones RN (2008) Antimicrobial activity of tigecycline and other broad spectrum antimicrobials tested against serine carbapenemase- and metallo{beta}-lactamase–producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance program. Antimicrob Agents Chemother 52:570–573. Clinical and Laboratory Standards Institute (CLSI) (2006) Performance standards for antimicrobial susceptibility testing; sixteenth informational supplement, M100-S16. CLSI: Wayne (PA). Curcio D, Fernandez F (2007) Acinetobacter spp. Susceptibility to tigecycline: a worldwide perspective. J Antimicrob Chemother 60: 449–450. Ellis-Grosse EJ, Babinchak T, Dartois N, Rose G, Loh E (2005) The efficacy and safety of tigecycline in the treatment of skin and skin-structure infections: results of 2 double-blind phase 3 comparison studies with vancomycin–aztreonam. Clin Infect Dis 41:S341–S353.
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