Journal of Chemotherapy Vol. 17 - n. 4 (361-366) - 2005 © E.S.I.F.T. srl - Firenze ISSN 1120-009X INTRODUCTION The members of the Enterococcus genus are Gram-positive, catalase-negative cocci and present in the normal flora of the gastrointestinal tract. However, they can be significant pathogens causing endocarditis, urinary tract, bloodstream and wound infections, especially in elderly patients with serious underlying diseases and immunocompromised patients who have been hospitalized for prolonged periods, use invasive devices or have received broad spectrum antimicrobial therapy. Recently, an increase in the occurrence of vancomycin-resistant enterococci (VRE) has been reported 1,2 . Six types of glycopeptide resistance have already been described among enterococci. Three of them are the most common: VanA, VanB, and VanC pheno- types. The genes associated with resistance have the same names as the phenotype, vanA, vanB and vanC, respectively. The vanA and vanB genes are found exclusively in Enterococcus faecium and E. faecalis, which are commonly isolated from human diseases. VanA-mediated resistance is associated with inducible high-level resistance to vancomycin The Resazurin Microplate Method for Rapid Detection of Vancomycin Resistance in Enterococci A.Y. COBAN 1 - O. DARKA 1 - N.T. FISGIN 2 - C.C. CIHAN 1 - K. BILGIN 1 - A. AKGUNES 1 T. GUVEN 3 - B. DOKUZOGUZ 3 - A. BIRINCI 1 - B. DURUPINAR 1 1 Ondokuz Mayis University, Medical School, Department of Microbiology and Clinical Microbiology, Samsun, Turkey. 2 Ondokuz Mayis University, Medical School, Department of Clinical Microbiology and Infectious Diseases, Samsun, Turkey. 3 Ankara Numune Education and Research Hospital, The First Infectious Diseases and Clinical Microbiology Clinic, Ankara, Turkey. Corresponding author: Ahmet Yilmaz Coban, Ph.D., Ondokuz Mayis University, Medical School, Department of Microbiology and Clinical Microbiology, 55139 Samsun, Turkey. Tel: +90 362 4576000/3526; Fax: +90 362 4576041. E-mail: noahmet@yahoo.com Summary Vancomycin-resistant enterococci (VRE) are a serious challenge for physicians because of the limited treatment options for infections caused by this organism. Prevention of VRE transmission in hospitals requires early detection of infected or colonized patients. Therefore rapid and correct detection of vancomycin resistance is essential. In this study, we use the resazurin microplate method (RMM), which is a modification of the NCCLS and BSAC broth microdilution methods to rapidly determine the susceptibilities of clinical enterococci isolates to vancomycin. The alteration in the RMM was relevant to the final bacterial count. In this method, inoculum that was 10-fold higher than standard methods was used. A total of 80 enterococci, including 11 VRE isolates and 6 vancomycin intermediate isolates, were screened with this modified colorimetric broth microdilution method. After 4 h of incubation 30 µl of 0.01% resazurin solution were added to each well and the plates were reincubated for color change for 5-10 min. The MICs were obtained at the 4 th h. The results were in exact agreement with the NCCLS and the BSAC microdilution methods. Absolute and essential agreements were 100% and there were no minor, major or very major errors. In conclusion, this modified colorimetric broth microdilution method can be used as a reliable, easy, cheap and rapid method for early detection of VRE. Moreover, this method has the potential of being used to test the susceptibilities of different bacteria to other antibiotics. Key words: Enterococci, resazurin microplate method, vancomycin, VRE. REPRINT REVIEW