beta-Lactam resistance in Serratia marcescens: comparison of action of benzylpenicillin, Apalcillin, Cefazolin, and ceftizoxime.

The intrinsic mechanisms of resistance to beta-lactam antibiotics in Serratia marcescens IFO 12648 were investigated, comparing the action of benzylpenicillin, apalcillin, cefazolin, and ceftizoxime. The minimal inhibitory concentrations for this strain were 1,600, 3.13, 6,400, and 0.05 microgram/ml, respectively. The addition of ethylenediaminetetraacetic acid markedly reduced the minimal inhibitory concentrations of benzylpenicillin and cefazolin, whereas those of apalcillin and ceftizoxime were not influenced. S. marcescens IFO 12648 produced only a low level of beta-lactamase activity constitutively, and the production was considerably increased by the addition of benzylpenicillin. Cefazolin was hydrolyzed rapidly by beta-lactamase activity, whereas benzylpenicillin, apalcillin, and ceftizoxime were poorly hydrolyzed. Peptidoglycan synthesis in ether-treated strain IFO 12646 cells was inhibited by a concentration of ceftizoxime markedly lower than that of cefazolin and by a concentration of apalcillin moderately lower than that of benzylpenicillin.