German multicentre survey of the antibiotic susceptibility of Bacteroides fragilis group and Prevotella species isolated from intra-abdominal infections:results from the PRISMA study

OBJECTIVES: To determine the susceptibility of Gram-negative anaerobic bacteria of the family Bacteroidaceae from hospitalized patients with intra-abdominal infections (IAIs) to moxifloxacin and other antimicrobial agents with known activity against anaerobes.

METHODS: Four hundred and thirty anaerobic bacterial isolates of the family Bacteroidaceae obtained from patients with IAIs were collected from 32 centres in Germany in 2007. MICs were determined using microbroth dilution for the following antimicrobials: ampicillin/sulbactam; ertapenem; meropenem; levofloxacin; moxifloxacin; clindamycin; and metronidazole. EUCAST and CLSI guidelines (for moxifloxacin) were used for interpretation.

RESULTS: Overall, metronidazole exhibited the lowest resistance rates against the study isolates (four isolates, 0.9%), while the resistance rate was 4.9% for ampicillin/sulbactam, 5.3% for ertapenem and 4.9% for meropenem. Moxifloxacin showed good activity against most Bacteroides species. Resistance rates ranged between 10% and 22% for the various species except Bacteroides vulgatus, with 59% of isolates being resistant. Clindamycin had only poor activity, with 9%-56% of Bacteroides isolates being resistant.

CONCLUSIONS: Resistance among Bacteroides spp. involved in IAIs to antimicrobials with known activity against anaerobes does occur and the resistance rate observed for the carbapenems is a cause of concern. These data emphasize the need not only for periodic monitoring of the susceptibility of anaerobic pathogens to guide empirical treatment but also for species identification and susceptibility testing in selected patients with severe infections involving anaerobic bacteria.