Antibiotic Susceptibility of Bacteroides fragilis Group Organisms
Abstract & Commentary
Synopsis: Metronidazole, piperacillin/tazobactam, and the carbapenems remain the most reliably active against B fragilis group organisms.
Source: Aldridge KE, et al. Bacteremia due to Bacteroides fragilis group: Distribution of species, beta-lactamase production, and antimicrobial susceptibility patterns. Antimicrob Agents Chemother. 2003;47:148-153.
Aldridge and colleagues examined susceptibility test results of 542 bloodstream Bacteroides fragilis group isolates recovered from 1987 to 1999 at 12 US medical centers. B fragilis comprised 63% of the isolates, followed by B thetaiotamicron (18%), B ovatus (10%), B vulgatus (6%), and B diastonis (3%), with a few additional isolates of B uniformis and B cacae. Not all isolates were tested against all antibiotics.
One hundred percent of the isolates were resistant to penicillin, while 100% were susceptible to metronidazole. Imipenem and piperacillin/tazobactam were each active against > 99%. Ninety-three percent were susceptible to ampicillin/sulbactam, 98% to meropenem, and 94% to ertapenem. Cefoxitin was active against 84%, while cefotetan inhibited only 64%. Twenty-three percent of species other than B fragilis were susceptible to cefotetan. Twenty-two percent of isolates were resistant to clindamycin. Resistance to clindamycin was seen among all species tested, and only approximately one-half of both B diastonis and B ovatus isolates were susceptible to this drug. B fragilis demonstrated the greatest overall susceptibility among the species tested.
Comment by Stan Deresinski, MD, FACP
These results confirm those of other surveys published in recent years. While greater than 99% of B fragilis group isolates remain susceptible to metronidazole, imipenem, and piperacillin/tazobactam, increasing in vitro resistance to a number of other antibiotics used in mixed aerobic/anaerobic infections is occurring. Perhaps the most dramatic finding over the last decade or so has been the increased resistance to clindamycin reported to be 32% in this study. To the extent that these in vitro results predict clinical therapeutic outcome, clindamycin can no longer be relied upon for anaerobic coverage in infections in which B fragilis group isolates play a role.
Cefotetan, often used in the prophylaxis and therapy of mixed aerobic anaerobic infections, also performed poorly, with 36% of isolates resistant. Cefoxitin performed significantly better than cefotetan, with 16% resistant.
The bottom line: Metronidazole, piperacillin/tazobactam, and the carbapenems remain the most reliably active against B fragilis group organisms.
Metronidazole, piperacillin/tazobactam, and the carbapenems remain the most reliably active against B fragilis group organisms.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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