Comparative in-vitro activity of meropenem on clinical isolates from the United Kingdom

MICs of meropenem were determined for a wide range of common bacteria of clinical importance. For Enterobacteriaceae, Aeromonas spp., Haemophilus influenzae, Branhamella catarrhalis, Neisseria gonorrhoeae, Gardnerella vaginalis, Campylobacter coli/jejuni, beta-haemolytic streptococci and anaerobes other than Clostridium difficile, MICs were almost always within the range 0.002-0.5 mg/l. The activity of meropenem for these organisms was always greater than that of imipenem and piperacillin, and was similar to that of ceftazidime and cefotaxime except that strains resistant to these latter, and to piperacillin, were usually sensitive to imipenem and meropenem. Meropenem was also active against most non-fermentative Gram-negative bacilli, with MICs in the range 0.12-4 mg/l but Pseudomonas (Xanthomonas) maltophilia was often resistant, as it was to all the other drugs tested. Staphylococci, Strreptococcus pneumoniae and other alpha-haemolytic streptococci were usually more sensitive to imipenem than to meropenem, but even methicillin-resistant staphylococci were sensitive to both drugs (MICs less than 4 mg/l). Enterococci were also less sensitive to meropenem than to imipenem, and Enterococcus faecium was invariably highly resistant to all the drugs tested except ciprofloxacin, which had marginal activity. Results for Ps. maltophilia and Haem. influenzae were affected by media used for sensitivity testing.