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

• Published in: Journal of antimicrobial chemotherapy Vol. 60; no. 4; pp. 872 - 876
• Main Authors: Corvec, Stéphane, Prodhomme, Adèle, Giraudeau, Cécile, Dauvergne, Sandie, Reynaud, Alain, Caroff, Nathalie
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01-10-2007
• Subjects: Antibiotics. Antiinfectious agents. Antiparasitic agents; Bacterial Proteins - biosynthesis; beta-Lactamases - biosynthesis; Biological and medical sciences; cephalosporinase; DNA Fingerprinting; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; E. coli; Escherichia coli - classification; Escherichia coli - enzymology; Escherichia coli - genetics; Escherichia coli Infections - microbiology; Genotype; Humans; Medical sciences; Microbial Sensitivity Tests; Pharmacology. Drug treatments; Phylogeny; Point Mutation; Polymerase Chain Reaction - methods; Polymorphism, Genetic; promoter; Promoter Regions, Genetic; Random Amplified Polymorphic DNA Technique; Sequence Analysis, DNA; virulence; Virulence Factors - genetics; promoter; virulence; cephalosporinase; .; Enzyme; Escherichia coli; Virulence; Chromosome; Phylogeny; β-Lactamase; Strain; Promoter; Bacteria; Hydrolases; Genetics; E. coli; Enterobacteriaceae
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkm284

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 β-lactamase production (negative double-disc synergy test), were phylogrouped by multiplex PCR. As a comparison, 100 E. coli clinical isolates, susceptible to all β-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.