Comparison of mezlocillin, piperacillin, Bay k 4999 with carbenicillin and ticarcillin against enterobacteriaceae and Pseudomonas aeruginosa.

The minimal inhibitory concentration (MIC) of five penicillins (carbenicillin, ticarcillin, mezlocillin, piperacillin and Bay k 4999) against Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, indole positive Proteus sp. and Enterobacter species was determined by an agar dilution method. Bay k 4999 and piperacillin were found to be the most active of the semi-synthetic penicillins tested against P. aeruginosa and Enterobacteriaceae. Bay k 4999 was slightly more active than piperacillin against E. coli, about as active as piperacillin against Pseudomonas, K. pneumoniae, P. mirabilis and indole positive Proteus, but more active than piperacillin against Enterobacter species.