Synergic activity of beta-lactamines and aminoglycosides vs. bacterial strains treated with sub-MIC concentrations

The aim of the present paper was to evaluate the interaction between beta-lactamines and aminoglycosides against Gram-positive and Gram-negative bacteria previously treated with sub-inhibitory doses of each antibiotic in the combination. Bacterial strains were: S. aureus ATTC 25923, S. mitis NCTC 3165, E. coli ATTC 25922, P. vulgaris ATTC 13315. Antibiotics used were penicillin G and gentamicin. The most synergistic combination was the ratio of 4 (penicillin G) to 1 (gentamicin) before and after sub-MIC treatment with penicillin.