In vitro activity of sulbactam in combination with various beta-lactam antibiotics.

Forty-three strains (beta-lactamase positive and negative) from the species of Haemophilus influenzae, Neisseria gonorrhoeae, Staphylococcus aureus, Escherichia coli, Serratia marcescens, Enterobacter cloacae, Acinetobacter baumanii, and Pseudomonas aeruginosa were studied for synergy between sulbactam and several beta-lactam antibiotics. Using a checkerboard method, synergy was observed with 10 to 55% of the beta-lactamase negative strains. Synergy was more frequent with the strains producing beta-lactamase. Using the killing curve method, synergy was also observed between sulbactam and beta-lactam antibiotics against some beta-lactamase negative strains. In addition, the regrowth of a resistant subpopulation was prevented by sulbactam.