Cephabacins, new cephem antibiotics of bacterial origin. IV. Antibacterial activities, stability to .BETA.-lactamases and mode of action.

Abstract
Cephabacin F group antibiotics with a 7-formylamino substituent showed antibacterial activity against a wide variety of bacteria including .beta.-lactamase-producing clinical isolates and anaerobic bacteria. Cephabacin H group antibiotics without the substituent showed more potent activity against gram-positive bacteria than cephabacin F group antibiotics, but were not active against gram-negative bacteria producing .beta.-lactamases. Cephabacin F group antibiotics were highly resistant to hydrolysis by various types of .beta.-lactamases and showed strong inhibitory activity against a cephalosporinase of Proteus vulgalis GN4413 due to the 7-formylamino substituent. Mode of action of cephabacin F1 and H1 was examined using Escherichia coli and Bacillus subtilis as the test organisms. They showed strong lytic activity against these organisms and inhibited their peptidoglycan synthesis. Cephabacin F11 had the highest affinity for penicillin-binding protein (PBP) 1 in E. coli and PBP 4 in B. subtilis. Cephabacins showed a protective effect in experimentally infected mice.

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