Antibacterial properties of meropenem towards clinical isolates, beta-lactamase producers and laboratory mutants.

Clinical isolates (1017) obtained from a multicentre study were examined. The activity of meropenem was better than that of imipenem against Enterobacteriaceae and Pseudomonas aeruginosa. Meropenem was slightly less active against staphylococci than was imipenem. Meropenem had little activity against enterococci (MIC90, 16 mg/l). Mutants selected with imipenem or meropenem remained more sensitive to meropenem but MICs increased for both drugs. Other resistance mechanisms such as beta-lactamases or aminoglycoside modifying enzymes did not influence meropenem activity with the exception of beta-lactamase from Ps. cepacia.