Affiliation:
1. Service de Microbiologie, Hôpital Saint-Louis,1 and
2. Service de Microbiologie, Hôpital Boucicaut,2 Paris, France
Abstract
ABSTRACT
DHA-1, a plasmid-mediated cephalosporinase from a single clinical
Salmonella enteritidis
isolate, conferred resistance to oxyimino-cephalosporins (cefotaxime and ceftazidime) and cephamycins (cefoxitin and moxalactam), and this resistance was transferable to
Escherichia coli
HB101. An antagonism was observed between cefoxitin and aztreonam by the diffusion method. Transformation of the transconjugant
E. coli
strain with plasmid pNH5 carrying the
ampD
gene (whose product decreases the level of expression of
ampC
) resulted in an eightfold decrease in the MIC of cefoxitin. A clone with the same AmpC susceptibility pattern with antagonism was obtained, clone
E. coli
JM101(pSAL2-ind), and its nucleotide sequence was determined. It contained an open reading frame with 98.7% DNA sequence identity with the
ampC
gene of
Morganella morganii
. DNA sequence analysis also identified a gene upstream of
ampC
whose sequence was 97% identical to the partial sequence of the
ampR
gene (435 bp) from
M. morganii
. The gene encoded a protein with an amino-terminal DNA-binding domain typical of transcriptional activators of the LysR family. Moreover, the intercistronic region between the
ampC
and
ampR
genes was 98% identical to the corresponding region from
M. morganii
DNA. AmpR was shown to be functional by enzyme induction and a gel mobility-shift assay. An
ampG
gene was also detected in a Southern blot of DNA from the
S. enteritidis
isolate. These findings suggest that this inducible plasmid-mediated AmpC type β-lactamase, DHA-1, probably originated from
M. morganii.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
128 articles.
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