PS-6 and PS-7, new .BETA.-lactam antibiotics. In vitro and in vivo evaluation.

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Abstract
Biological properties of two new β-lactam antibiotics, PS-6 and PS-7, containing the carbapenem nucleus were studied. The in vitro activities of PS-6 and PS-7 were tested against Bclinical isolates of Gram-positive and Gram-negative bacteria in comparison with those of cefazolin, ampicillin and PS-5. In general, the antibacterial spectra of PS-6 and PS-7 were similar to that of PS-5. PS-7 was slightly less active than PS-5 and ABPC against Staphylococcus aureus. Clinical isolates of Gram-negative bacteria were found to be 2- to 8-fold more resistant to PS-6 than to PS-5, while PS-7 was 2-fold more active than PS-5 against Enterobacter, Klebsiella, Proteus, Serratia and Escherichia coli. The therapeutic effect of PS-6 seemed slightly less than that of PS-5 in an experimental infection with Staph. aureus Smith in mice.