Bactericidal and synergistic activity of moxalactam alone and in combination with gentamicin against Pseudomonas aeruginosa.

The bactericidal activity of moxalactam, alone and in combination with gentamicin, was studied with macrobroth two-dimensional checkerboard and killing curve techniques against gentamicin-resistant and -susceptible strains of Pseudomonas aeruginosa. Moxalactam was bactericidal at concentrations equal to or at least two to four times its inhibitory concentrations. Synergy at clinically applicable concentrations of moxalactam and gentamicin occurred with 6 of 14 gentamicin-resistant strains and 4 of 4 gentamicin-susceptible strains by the checkerboard technique and with 7 of 14 gentamicin-resistant strains by the killing curve technique. Synergy between moxalactam and gentamicin against gentamicin-resistant strains of P. aeruginosa is unpredictable and strain- and method-dependent.