Antimicrobial susceptibility patterns of anaerobic bacteria in Victoria, Australia.

Mortality associated with anaerobic infections approximates 20%. Resistance of anaerobic bacteria to commonly used antimicrobials has been increasingly reported. The aim of this study was to describe antimicrobial susceptibility patterns of anaerobic bacteria isolated from clinical samples using a gradient diffusion method, E test (bioMerieux), in Victoria, Australia. Metronidazole, meropenem and amoxycillin-clavulanate were found to be active against almost all isolates tested. Most Gram positive anaerobic cocci (GPAC), except Peptostreptococcus anaerobius (64.6% penicillin-susceptible), remained susceptible to penicillin. All Clostridium perfringens isolates tested were penicillin, metronidazole and meropenem susceptible. Of B. fragilis isolates tested, 5% and 0.83% were meropenem and metronidazole non-susceptible, respectively. Clindamycin susceptibility in anaerobes other than the GPAC is approximately 75% and therefore should not be used as empirical treatment in the absence of susceptibility testing. Considering the global trend of antibiotic resistance among anaerobic bacteria, routine susceptibility testing of anaerobic bacteria, particularly when isolated from critical sites, as well as surveillance of local resistance trends is strongly encouraged. Gradient diffusion MIC determination of anaerobic bacteria is feasible in a clinical diagnostic laboratory and should be more widely utilised.