The antibacterial activity of meropenem in combination with gentamicin or vancomycin

The kinetics of bacterial killing by meropenem alone and in combination with gentamicin (for Pseudomonas aeruginosa) and vancomycin (for Staphylococcus aureus) were studied for two strains of each species. Against the two strains of P. aeruginosa, meropenem at concentrations up to 4 x MIC was rapidly bactericidal--but regrowth occurred by 24 h. The addition of half the MIC of gentamicin to the MIC of meropenem led to a more rapid decline of the colony count and to the prevention of regrowth of the strain which was gentamicin-susceptible. Similar results were obtained for a methicillin-susceptible strain of S. aureus when vancomycin was added at a concentration of half the MIC. A methicillin-resistant strain also was killed by a combination of vancomycin at half the MIC plus meropenem at the MIC. The study showed that the killing action of meropenem against P. aeruginosa and staphylococci is enhanced by the addition of gentamicin or vancomycin respectively.