Minimum inhibitory concentration values and problematic disk break points of tigecycline against vancomycin and/or high-level aminoglycoside-resistant enterococci

Dolapci, Istar/0000-0002-6443-4612WOS: 000390144800004Background: Tigecycline is a new, semisynthetic glycylcycline. It is active against important multidrug resistant pathogens. Aim: The purpose of this study was to investigate the sensitivity of multidrug-resistant enterococci to tigecycline, and to test the correlation between the minimal inhibitory concentration (MIC) and disk diffusion methods. Materials and methods: The antimicrobial sensitivity of 108 multidrug-resistant isolates, which included 52 vancomycin-resistant enterococci (VRE) and 56 high-level aminoglycoside-resistant (HLAR) enterococci, was tested by the E test, broth microdilution test and disk diffusion methods. Results: All of the isolates were sensitive to tigecycline, as determined by the E test and broth microdilution test. The MIC 90 value (0.19 mu g/mL) of tigecycline for HLAR enterococci was higher than that for VRE (0.094 mu g/mL). When results were evaluated according to species, the MIC values of tigecycline for Enterococcus faecalis were higher than those for the other species. Eleven (10.1%) isolates produced false resistance results (zone diameter 615 mm) by the disk diffusion method. These cases were classified as major errors. Eight (7.4%) isolates had intermediate sensitivity (sensitivity zone of 16 or 17 mm), which were classified as minor errors. The major and minor error percentages of HLAR enterococci (14.2% major, 10.7% minor error) were higher than those of VRE (5.7% major, 3.8% minor error). These results indicate that tigecycline is effective against multidrug-resistant enterococci. The sensitivity of multidrug-resistant enterococci to tigecycline should be investigated by MIC methods. The disk diffusion method causes major errors, especially for HLAR enterococci. (C) 2015 The Authors. Alexandria University Faculty of Medicine. Production and hosting by Elsevier B.V.Kirikkale University Scientific Research UnitKirikkale UniversityThis study was supported by Kirikkale University Scientific Research Unit