Synergistic action between sisomicin and mezlocillin against gram-negative bacteria and Staphylococcus aureus

The combined effect of sisomicin and 6-[(R)-2-[3-methylsulfonyl-2-oxo-imidazolidine-1-carboxamido]-2-phenyl-acetamido-a1-penicillanic acid sodium salt (mezlocillin, Baypen) was studied against 50 bacterial strains, including Pseudomonas aeruginosa, Proteus spp. Klebsiella-Enterobacter, E. coli and Staphylococcus aureus. No antagonism or indifference was detected with the strains studied. Both antibiotics were synergistic against 62% of the strains, and partially synergistic against 38%. Out of the bacteria studied, Staphylococcus aureus was the most susceptible to the combined action of sisomicin and mezlocillin.