High incidence of cefoxitin and clindamycin resistance among anaerobes in Taiwan

Abstract

Susceptibilities to 16 antimicrobial agents were determined by measurement of MICs for 344 isolates of anaerobic bacteria recovered from patients with significant infections. Resistance rates varied among antimicrobial agents and the species tested. The beta-lactams were more active in gram-positive than in gram-negative anaerobes. Resistance to meropenem was low (<1%). For beta-lactam-beta-lactamase inhibitors, piperacillin-tazobactam was most active for all species (resistance, <6%). The rates of resistance to cefoxitin (31 to 65%) and clindamycin (50 to 70%) for non-Bacteroides fragilis species of the B. fragilis group were higher than those for B. fragilis (4% resistant to cefoxitin and 33% resistant to clindamycin). Among members of B. fragilis group, Bacteroides thetaiotaomicron was the most resistant to clindamycin (70%) and cefoxitin (65%). Rates of susceptibility to imipenem and metronidazole for B. fragilis continue to be high compared to those from a previous study 10 years ago. However, resistance to metronidazole was found recently in five strains of B. fragilis. We analyzed the genetic relationships among the metronidazole-resistant B. fragilis strains by pulsed-field gel electrophoresis. The metronidazole-resistant B. fragilis strains showed genotypic heterogeneity, excluding the dissemination of a single clone.

FIG. 1.

Rates of susceptibility to six routinely tested agents in all of the Bacteroides species isolates at National Taiwan University Hospital from 1977 to 2000. Susceptibility testing was performed by the disk diffusion method before 1990 and by the breakpoint agar dilution method after 1991. SAM, ampicillin- sulbactam.

FIG. 2.

PFGE analysis of XbaI-digested genomic DNA from B. fragilis isolates. Lane M, lambda ladder molecular size markers; lanes 1 to 6, metronidazole-nonsusceptible B. fragilis isolates (lanes 2 and 3, isolates from the same individual); lanes 7 to 9, metronidazole-susceptible B. fragilis isolates.