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Indian Journal of Medical Microbiology, Vol. 27, No. 4, October-December, 2009, pp. 373-374 Correspondence Comparative in vitro antimicrobial activity of tigecycline against clinical isolates of vancomycin-resistant enterococcus *M Yemisen, A Demirel, B Mete, A Kaygusuz, A Mert, F Tabak, R Ozturk Department of Infectious Diseases and Clinical Microbiology (MY, AD, BM, AM, FT, RO), Department of Microbiology (AK), Cerrahpasa School of Medicine, Istanbul University, Istanbul, Turkey. Correspondence Address: *Department of Infectious Diseases and Clinical Microbiology, Cerrahpasa School of Medicine, Istanbul University, Istanbul, Turkey, yemisenmucahit@hotmail.com Date of Submission: 02-Nov-2008 Code Number: mb09105 PMID: 19736414 DOI: 10.4103/0255-0857.55455 Dear Editor, In last four decades, tetracyclines have been widely used due to their broad-spectrum of antimicrobial activity against Gram-positive and Gram-negative bacteria. However, indications for the use of tetracyclines have been limited due to the emergence of resistant strains. Tigecycline, [1] former GAR-936, is the first representative of a new class of antimicrobial agents known as glycylcyclines. Tigecycline may be an alternative for the treatment of Vancomycin-resistant Enterococcus (VRE), one of the most important and emerging causes of human nosocomial infections. In this study, we evaluate the In vitro activity of tigecycline in comparison to other antimicrobial agents against VRE isolates obtained from the patients followed in our university hospital. About 22 Enterococcus faecalis and six Enterococcus faecium isolates were obtained from clinical materials (19 urine, nine blood) of hospitalised patients. Patients with VRE blood stream infection were followed in the intensive care unit, had central venous catheter and severe underlying diseases. Isolates were identified to genus level by Gram staining, L-pyrrolindonyl-b-naphthylamide reaction, catalase reaction, bile esculin test, salt tolerance and streptococcal grouping. Identification to species level was performed using the API Rapid ID 32 Strep system (BioMe´rieux, Marcy l'Etoile, France). Antibiotic susceptibility testing was performed by disk diffusion, as recommended by the Clinical Laboratory Standard Institute [2] (CLSI, formerly NCCLS). For isolates not fully susceptible to vancomycin, the MIC of vancomycin was determined by Etest (AB Biodisk, Solna, Sweden), using the high-inoculum method on Mueller-Hinton agar. All 28 isolates, obtained from cultures were stored in brain-heart infusion broth at -70ºC. In this study, antimicrobial susceptibility testing was performed against eight antimicrobial agents by using broth microdilution method, as described by the CLSI. Minimal inhibitory concentration (MIC) was defined as the lowest concentration of antimicrobial agent producing no visible growth of microorganism at 37ºC after overnight incubation. MIC 50 and MIC 90 was determined by the concentrations of antimicrobial agent at which 50% and 90% of microorganism are inhibited, respectively. We decided to determine both MIC 50 and MIC 90 values to show the potency of anibiotics. The following quality control strains were concurrently tested by using E. faecalis ATCC 29212 and E. faecium ATCC 6057. Results of the In vitro susceptibility testing are presented in [Table - 1]. The antimicrobial activity of tigecycline was compared to those selected antimicrobial agents. Tigecycline was highly active against VRE. MIC 50 and MIC 90 values were 0.06 and 0.12 µg/mL, respectively and same for E. faecalis and E. faecium isolates. Only one islolate showed a MIC value of 0.5 µg/mL over 0.25 µg/mL and the tigecycline MIC range of the isolates was between 0.03 and 0.5 µg/mL. The vast majority of strains showed high MIC values against other antibiotics. Linezolid was another antibiotic with low MIC 50 and MIC 90 values, which was 4 µg/mL for both. In conclusion, VRE is an emerging problem and antibiotic sources are limited. Our study agrees with previous In vitro studies [3],[4] and shows that tigecycline has high In vitro activity against VRE. These results suggest that further prospective clinical studies must be performed and tigecycline may have an important role in the treatment of severely ill patients infected with VRE. Acknowledgments This study was funded by Wyeth Pharmaceuticals. References
Copyright 2009 - Indian Journal of Medical Microbiology The following images related to this document are available:Photo images[mb09105t1.jpg] |
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