Affiliation:
1. Department of Microbiology, Kitasato University School of Medicine, Sagamihara,1 and
2. Medicinal Biology Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Osaka,2 Japan
Abstract
ABSTRACT
Enterobacter cloacae
8009 produced an inducible class A β-lactamase which hydrolyzed cefotaxime efficiently. It also hydrolyzed other β-lactams except cephamycins and carbapenems. The activity was inhibited by clavulanic acid and imipenem. The
bla
gene was transferable to
Escherichia coli
by electroporation of plasmid DNA. The molecular mass of the β-lactamase was 29 kDa and its pI was 7.3. All of these phenotypic characteristics of the enzyme except for inducible production resemble those of some extended-spectrum class A β-lactamases like FEC-1. The gene encoding this β-lactamase was cloned and sequenced. The deduced amino acid sequence of the β-lactamase was homologous to the AmpA sequences of the
Serratia fonticola
chromosomal enzyme (96%), MEN-1 (78%),
Klebsiella oxytoca
chromosomal enzymes (77%), TOHO-1 (75%), and FEC-1 (72%). The conserved sequences of class A β-lactamases, including the S-X(T)-X(S)-K motif, in the active site were all conserved in this enzyme. On the basis of the high degree of homology to the β-lactamase of
S. fonticola
, the enzyme was named SFO-1. The
ampR
gene was located upstream of the
ampA
gene, and the AmpR sequence of SFO-1 had homology with the AmpR sequences of the chromosomal β-lactamases from
Citrobacter diversus
(80%),
Proteus vulgaris
(68%), and
Pseudomonas aeruginosa
(60%). SFO-1 was also inducible in
E. coli
. However, a transformant harboring plasmid without intact
ampR
produced a small amount of β-lactamase constitutively, suggesting that AmpR works as an activator of
ampA
of SFO-1. This is the first report from Japan describing an inducible plasmid-mediated class A β-lactamase in gram-negative bacteria.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
77 articles.
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