Effect of inoculum size on bacteriolytic activity of cefminox and four other b-lactam antibiotics against Escherichia coli. Antimicrob. Agents Chemother

MICs and turbidimetric experiments revealed a negligible inoculum effect with two Escherichia coli strains exposed to cefminox and cefoxitin, whereas a marked inoculum effect was revealed after exposure to cefotaxime, ceftizoxime, and imipenem. The activities of the cephamycins were associated with spheroplast formation and bacteriolysis at concentrations close to the MIC, whereas the other agents induced the formation of filaments or, in the case of imipenem, rounded cells. Cefminox is a semisynthetic cephamycin which is re-ported to be more active than other cephamycins against members of the family Enterobacteriaceae and Bacteroides fragilis (4, 14), to exhibit favorable pharmacokinetic proper-ties (5), and to be more active than- several other P,-lactam compounds in the treatment of systemic infections in mice (4). To explore these differences further, we examined the turbidimetric, bactericidal, and morphological responses of two Escherichia coli strains, ATCC 25922 and clinical isolate S31, to cefminox, 'cefoxitin, ceftizoxime, cefotaxime, an