Enterobacter cloacaeのβ-lactamaseとceftizoxime感受性について

概要

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Susceptibility of Enterobacter cloacae to ceftizoxime was distinguishable from that of Escherschia coil or Klebsiella pneumoniae in its heterogeneous distribution. The participation of β-lactamase in this heterogeneous susceptibility of E. cloacae was investigated. One hundred clinical isolates of E. cloacae were classified into fifteen groups according tothe isoelectric points of their chromosomal β-lactamases, which ranged from 8.8 to 10.1. Eighteen strains produced plasmid-mediated penicillinase (PI=5.5) together with chromosomal β-lactamese. Most strains fell under A group (PI=8.8, 39%), followed by G group (PI=9.5, 24%). The distribution profileof ceftizoxime susceptibility of each group was not much different from that of the gross of E. cloacae strains. Meanwhile, β-lactansaae productivity of E. cloacae varied widely with strains and the productivity either in the absence or presence of an inducer correlated well with susceptibility to ceftizoxime among the strains of the same group. These results suggest that the heterogeneous susceptibility of E. cloacae to ceftizoxime arises not from the presence of subspecies in E. cloacae but from a wide variety of β-lactamase productivity of E. cloacae strains. Plasmid-mediated penicillinase scarcely affected the susceptibility of E. cloacae to ceftizoxime whereas it reduced markedly the susceptibility to cefoperazone.
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