In-vitro activity of meropenem against clinical isolates obtained in Canada

The in-vitro activity of meropenem, a new parenteral carbapenem, was compared with that of imipenem, ceftazidime, cefotaxime, piperacillin, gentamicin and, where appropriate, other antibiotics against recent clinical isolates and characterized beta-lactamase producers. MICs were determined by a standard agar dilution procedure and two inocula (10(4) and 10(6) cfu) were used throughout. Meropenem inhibited 90% of isolates of Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, indole-positive Proteus spp., Enterobacter spp., Serratia marcescens and Providencia stuartii at less than or equal to 0.25 mg/l and was four- to 16-fold more active than imipenem against these species. Against the enteric pathogens Salmonella typhi, Shigella sonnei, Yersinia enterocolitica and Campylobacter jejuni, meropenem was four- to eight-fold more active than imipenem, inhibiting all isolates at less than or equal to 0.03 mg/l. Meropenem was also more active than imipenem against Haemophilus influenzae (MIC90 0.06 mg/l) but had similar activity against the Bacteroides fragilis group (MIC90 0.25 mg/l), against Pseudomonas aeruginosa (MIC90 2 mg/l) and against streptococci. Imipenem was four-fold more active than meropenem against Acinetobacter spp. and two- to eight-fold more active against all species of staphylococci tested. Both meropenem and imipenem were inactive against Ps. (Xanthomonas) maltophilia.