Comparison of the activity of meropenem and imipenem against anaerobic bacteria in Bulgaria

The in vitro activities of meropenem and imipenem were compared against 154 clinical isolates of anaerobic bacteria representing 23 species of 10 gene ra. The NCCLS-recommended agar dilution method with Brucella agar from the Wadsworth Anaerobic Laboratory was used. Meropenem proved to be more active than imipenem with an MIC range of less than or equal to 0.125-4 mu g/mL, MIC50=0.25 mu g/mL, MIC90=1 mu g/mL with 100% of strains susceptible at the breakpoint=4 mu g/mL. Imipenem showed a lower activity with an MIC range o f less than or equal to 0.125 to 16 mu g/mL, MIC50 of 2 mu g/mL and MIC90 o f 4 mu g/mL with 10% of the strains not inhibited at this concentration. Ni nety-six per cent were susceptible at 8 mu g/mL and 100% at 16 mu g/mL. The MIC of both antibiotics (especially of imipenem) were higher for the Bacte roides fragilis group than for the rest of the Gram-negative organism highe r still than the Gram-positive anaerobes. (C) 1999 Academic Press.