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J Antimicrob Chemother. 2007 Oct;60(4):872-6. Epub 2007 Jul 27.

Most Escherichia coli strains overproducing chromosomal AmpC beta-lactamase belong to phylogenetic group A.

Author information

1
Laboratoire de Bactériologie-Hygiène, CHU, Nantes, France.

Abstract

OBJECTIVES:

To determine the phylogenetic group and the production of different virulence factors (VFs) of a collection of Escherichia coli strains overproducing their chromosomal AmpC cephalosporinase.

METHODS:

Fifty-five E. coli strains, isolated over a 12 year period, and previously identified as AmpC overproducers by increased MICs of third-generation cephalosporins without extended-spectrum beta-lactamase production (negative double-disc synergy test), were phylogrouped by multiplex PCR. As a comparison, 100 E. coli clinical isolates, susceptible to all beta-lactams, were also tested by the same method. The ampC promoter sequence was determined for all these isolates. ERIC-2 PCR (where ERIC stands for enterobacterial repetitive intergenic consensus) was used to compare the isolates. Search for virulence-associated genes (papG alleles, sfa/foc, hly and iucC) was performed by multiplex PCR for the 55 AmpC overproducers.

RESULTS:

Most of the AmpC overproducers (47/55) belonged to phylogenetic group A, correlated with a low prevalence of the main VFs in these strains. The - 32, -42 and - 11 mutations, responsible for AmpC overproduction, were usually associated with DNA polymorphisms at positions - 88, - 82, -18, +1 and + 58 in the ampC promoter. In the control susceptible isolates, these polymorphisms were detected in 13 ampC promoters (9 group B1 and 4 group A). These polymorphisms were never associated with the main phylogenetic group B2, representing 66% of the susceptible isolates.

CONCLUSIONS:

AmpC overproduction was clearly correlated with non-virulent commensal phylogenetic groups A and B1, and absence of the main E. coli VFs. Susceptible isolates harbouring the same sequence polymorphisms as AmpC overproducers also belonged to commensal phylogenetic groups.

PMID:
17660264
DOI:
10.1093/jac/dkm284
[Indexed for MEDLINE]

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