Comparison of the in vitro activity of Bay k 4999 and piperacillin, two new antipseudomonal broad-spectrum penicillins, with other beta-lactam drugs.

Bay k 4999 and piperacillin, two new substituted ampicillins, were compared with other beta-lactam antibiotics, including carbenicillin, azlocillin, mezlocillin, benzylpenicillin, ampicillin, and cefoxitin, against a wide range of gram-positive and -negative organisms. Bay k 4999 and piperacillin were extremely active against Pseudomonas aeruginosa (50% inhibited by 2 mug/ml), being about 16-fold more active than carbenicillin. Bay k 4999 was the most active drug against Escherichia coli (50% inhibited by 0.5 mug/ml) and Klebsiella spp. (50% inhibited by 2 mug/ml). Piperacillin and Bay k 4999 were equally active against Proteus spp., and piperacillin had high activity against Bacteroides fragilis (50% inhibited by between 1 and 2 mug/ml).