Comparative bactericidal and morphological effects of five cephamycins on cells of three gram-negative bacilli at decreasing drug concentrations.

The bactericidal and morphological effects under drug-decreasing conditions of cefminox (MT-141), cefoxitin, cefmetazole, cefotetan and latamoxef were compared on Klebsiella pneumoniae PCl-602, Escherichia coli No. 29 and Serratia marcescens No. 1 cells. A new drug-decreasing method was developed by the use of an antibiotic removal device. Cefminox displayed an earlier onset and a higher rate of bactericidal action than the other cephamycins against the test organisms, although the minimum inhibitory concentrations of cefminox were similar to or higher than those of the other drugs. Morphologically, cefminox caused rapid lysis of the cells without filamentation, whereas the reference cephamycins caused mainly elongation of the cells under the test conditions. Frequent formation of multiple bulges on cells exposed to cefminox was observed in an isotonic medium.