In vitro activity of tigecycline and comparators against a European collection of anaerobes collected as part of the Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) 2010-2016

The Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) is a global program that aims to monitor the in vitro antimicrobial activities of current therapeutic agents against clinical isolates. This study presents surveillance data for Gram-positive and Gram-negative anaerobic isolates (N = 7008) collected from nine European countries between 2010 and 2016. Presented in this study are antimicrobial susceptibility data, according to the European Committee for Antimicrobial Susceptibility Testing (EUCAST) breakpoints, and minimum inhibitory concentration (MIC) distributions. The antimicrobial agents tested were cefoxitin (Gram-negative isolates only), clindamycin, meropenem, metronidazole, penicillin (Gram-positive isolates only), piperacillin-tazobactam and tigecycline. Among all Gram-positive and Gram-negative anaerobes, the lowest rates of resistance were to meropenem and metronidazole (0.0%-1.7% and 0.0%-1.9%, respectively). High rates of resistance were reported to clindamycin, in particular among isolates of the Bacteroides fragilis group (22.1%-48.1%) and Prevotella spp. (10.9%-32.2%). The majority of MIC distributions were unimodal, with the exception of clindamycin, which were mostly bimodal. Fifty percent of Gram-negative isolates gave tigecycline MICs between 0.06 and 1 mg/L, and 50% of Gram-positive isolates exhibited tigecycline MICs between 0.06 and 0.25 mg/L. The findings of this study suggest that the majority of anaerobic isolates were susceptible to meropenem and metronidazole, and that tigecycline remained active, but clindamycin resistance is a cause for concern in Europe. Surveillance studies, such as T.E.S.T., provide information on changes in the susceptibility of clinically important pathogens to commonly prescribed antimicrobial agents, and can highlight problems of antimicrobial resistance that need to be addressed.