Synergism of PS-5 with penicillins and cephalosporins in antimicrobial activity against beta-lactam-resistant gram-negative microorganisms.

The in vitro synergism of PS-5 combined with various penicillins and cephalosporins in antimicrobial activity was examined in detail against beta-lactam-resistant Gram-negative bacteria. PS-5 showed a highly significant synergism in antimicrobial action against Escherichia coli RGN238 in combination with penicillins; and against Proteus vulgaris GN76 and Serratia marcescens T55 in combination with cephalosporins. It was moderately synergistic against Citrobacter freundii GN346, Enterobacter cloacae 45, Proteus morganii 111 and Enterobacter aerogenes E19, whereas no synergism was observed against Pseudomonas aeruginosa E2 and Klebsiella pneumoniae 130.