Comparative in vitro activity of Bay k 4999 and piperacillin

The in vitro activity of piperacillin, a semisynthetic piperazine penicillin with excellent activity against Enterobacteriaceae, Pseudomonas aeruginosa and enterococci was compared to that of Bay k 4999, a new acylureidopenicillin. The inhibitory activity of both antibiotics against 228 clinical bacterial isolates was approximately equivalent at 64 μ/ml. At lower concentrations, piperacillin inhibited more strains of Pr. aeruginosa, enterococci and gentamicin-sensitive serratia than Bay k 4999. Conversely, Bay k 4999 had greater activity than piperacillin against Escherichia coli and enterobacter at lower concentrations. However, 36% of all Escherichia cali were resistant to both. These antibiotics have a significantly wider spectrum of activity than currently available semisynthetic penicillins.