In vitro antibacterial activity of meropenem, a new carbapenem antibiotic

The in vitro activity of the new carbapenem, meropenem (MEPM) was tested in comparison with imipenem (IPM), ceftazidime, cefotaxime, latamoxef and flomoxef. MEPM showed good activity against a broad spectrum of gram-positive and gram-negative standard bacteria, including Pseudomonas aeruginosa. The activity of MEPM against gram-positive cocci was about one-fourth that of IPM. MEPM was highly active against gram-negative bacteria, inhibiting all Enterobacteriaceae, except for 25% of Serratia marcescens isolates, at a concentration of 0.78 µg/ml. MEPM also showed a high activity against P. aeruginosa, its activity being two-fold higher than that of IPM. Against anaerobes, MEPM also had the best activity of the β-lactams tested. The compound was inactive against methicillin-resistant staphylococci, Enterococcus faecium, Xanthomonas maltophilia and Flavobacterium spp., as were the other β-lactams. MEPM also showed bactericidal activity against clinical isolates of methicillin-susceptible Staphylococcus aureus, Escherichia coli, Proteus vulgaris and P. aeruginosa at the MIC or at concentrations slightly above the MIC. MEPM was quite stable against various types of β-lactamase, but was hydrolyzed by X. maltophilia L-1 type β-lactamase, as were IPM and other β-lactams. This high degree of stability was responsible for the potent activity of MEPM against β-lactamase-producing species such as Enterobacter cloacae, Citrobacter freundii and P. vulgaris.