Antimicrobial resistance patterns for clinical isolates of bacteroides fragilis group organisms isolated in 2009-2012 at a Korean hospital

Abstract

Periodic monitoring of antimicrobial resistance trends of clinically important anaerobic bacteria such as Bacteroides fragilis group organisms is required, because the resistance patterns may vary greatly depending on regions and routine susceptibility is often not determined. We determined the antimicrobial susceptibilities of clinical isolates of B. fragilis group organisms recovered in 2009-2012 in South Korea.B. fragilis group isolates were recovered from blood, body fluid and abscess specimens at a tertiary-care hospital. The species were identified by conventional methods, the ATB 32A system and MALDI-TOF MS. A total of 180 nonduplicate isolates used in this study were: 86 B. fragilis, 46 B. thetaiotaomicron, 20 B. vulgatus, 13 B. ovatus, 13 Parabacteroides distasonis and 2 B. uniformis. Antimicrobial susceptibility was determined by the CLSI agar dilution method. The MIC was defined as the concentration at which there was a marked reduction in growth: such as from confluent growth to a haze, less than 10 tiny colonies, or several normal-sized colonies. B. fragilis ATCC 25285 and B. thetaiotaomicron ATCC 29741 were used as controls.Cefoxitin, imipenem, and meropenem were highly active against all isolates, with resistance rates of less than 8%. The rate of resistance to piperacillin-tazobactam was 2% for B. fragilis and 0% for other Bacteroides species, but 13% for B. thetaiotaomicron isolates. High resistance rates were observed to piperacillin (67% and 63%), cefotetan (37% and 31%), and clindamycin (78% and 67%) for B. thetaiotaomicron isolates and other Bacteroides spp., respectively. The moxifloxacin resistance rates were 25% for other Bacteroides spp. The MIC range of tigecycline was 0.12-16 μg/mL for all B. fragilis group isolates and MIC50 and MIC90 were 1-2 μg/mL and 8 μg/mL, respectively. No isolates were resistant to chloramphenicol and metronidazole.Piperacillin-tazobactam, cefoxitin, imipenem, meropenem, chloramphenicol, and metronidazole remain active against B. fragilis group isolates. Continuous monitoring is necessary to demonstrate changes in antimicrobial susceptibility patterns of B. fragilis group isolates.