Affiliation:
1. Departments of Laboratory Medicine
2. Epidemiology, Albany Medical Center Hospital, Albany, New York
Abstract
ABSTRACT
Clinical isolates of
Enterobacteriaceae
with reduced susceptibilities to cephalosporins were collected from 1993 to 2000. The organisms were screened for the extended-spectrum β-lactamase (ESBL) phenotype, and plasmid extracts were screened for genetic markers by hybridization. A
bla
TEM
probe was derived from pUC19; other probes were derived from pACM1, the plasmid responsible for the first known appearance of an ESBL in our institution. These probes included
bla
SHV
,
int
,
aac(3)-Ia
,
dfrA1
, IS
6100
,
tetA
, IncM markers, and Anon 13, a marker for the
Klebsiella pneumoniae
chromosomal sequences that flank
bla
SHV-5
. There were 42 hybridization patterns among 237 isolates. Patterns designated pACM1-like occurred in 44% of the isolates (eight species) and were always associated with the clavulanic acid (CA)-susceptible ESBL phenotype. The TEM marker was not predictive of the ESBL phenotype. Mapping indicated the presence of an SHV marker and up to 7.5 kb of its flanking chromosomal sequences in three non-IncM plasmids obtained in transformation experiments. We theorize that this DNA segment spread to other plasmids from pACM1-like sources. CA insensitivity became more frequent with time and was usually associated with either the TEM marker or the absence of both
bla
markers. One plasmid-encoded enzyme with characteristics of an AmpC β-lactamase was observed in a transformant lacking both TEM and SHV markers. Although SHV type ESBLs were a continuing source of reduced susceptibility to cephalosporins in our institution, organisms with different resistance mechanisms were added to the hospital microflora in later years. These changes might be related, in part, to ESBL control strategies implemented in 1995.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
17 articles.
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