Comparison of the In Vitro Activity of Bay k 4999 and Piperacillin, Two New Antipseudomonal Broad-Spectrum Penicillins, with Other β-Lactam Drugs

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Abstract
Bay k 4999 and piperacillin, two new substituted ampicillins, were compared with other β-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 μg/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 μg/ml) and Klebsiella spp. (50% inhibited by 2 μg/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 μg/ml).