Bactericidal effect of combinations of cephalosporins with tobramycin on clinical isolates of Escherichia coli, Klebsiella and Staphylococcus aureus.

The antimicrobial activities of the cephalosporins cefazolin, cefotaxime, moxalactam or ceftazidime in combination with tobramycin against clinical isolates of E. coli, of Klebsiella, of beta-lactamase-negative and beta-lactamase-producing S. aureus strains were compared in vitro by the checkerboard technique. Antibiotic dilutions differed by small arithmetic increments. Favourable interactions occurred with each bacterial species. This trend applied to third-generation cephalosporins against E. coli and Klebsiella as well as to cefazolin against S. aureus. The antibiotics with already the highest intrinsic activity generally exhibited also the most favourable interaction.