Patterns of resistance to anaerobic organisms in Australia.

This study investigated patterns of resistance in anaerobic organisms isolated at Westmead Hospital in Sydney, Australia, during the years 1987 to 1988. Minimal inhibitory concentrations (MICs) to ampicillin, sulbactam/ampicillin, metronidazole, clindamycin, and cefoxitin were determined by agar dilution for 200 anaerobes from clinically significant infections. Antibiotics active against nearly all of these anaerobes included metronidazole and sulbactam/ampicillin, which demonstrated good activity against beta-lactamase producing Bacteroides spp. with the exception of Bacteroides distasonis. Resistance in non-beta-lactamase producing anaerobes was similar to that seen with ampicillin. As expected, ampicillin resistance was common in the Bacteroides fragilis group where beta-lactamase production was frequent. In addition, beta-lactamase was detected in 33% of other Bacteroides spp. Ampicillin resistance was also seen in 5 to 15% of additional anaerobes that did not produce beta-lactamase. Clindamycin resistance occurred in 4 to 18% of the B. fragilis group. Clindamycin resistance was also seen in 7 to 8% of Clostridium spp. and anaerobic Gram-positive cocci. Resistance to cefoxitin was variable in the B. fragilis group with the highest levels of resistance occurring in the indole-negative subgroup. Resistance in other anaerobes was not commonly seen.