Most Escherichia coli strains overproducing chromosomal AmpC beta-lactamase belong to phylogenetic group A.
OBJECTIVE
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.
Laboratoire de Bactériologie-Hygiène, CHU, Nantes, France.
Stéphane
S
Corvec
Adèle
A
Prodhomme
Cécile
C
Giraudeau
Sandie
S
Dauvergne
Alain
A
Reynaud
Nathalie
N
Caroff
D001426:Bacterial Proteins / Q000096:biosynthesis*; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000145:classification* / Q000201:enzymology* / Q000235:genetics; D004927:Escherichia coli Infections / Q000382:microbiology; D005838:Genotype; D006801:Humans; D008826:Microbial Sensitivity Tests; D010802:Phylogeny; D017354:Point Mutation; D016133:Polymerase Chain Reaction / Q000379:methods; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D019105:Random Amplified Polymorphic DNA Technique; D017422:Sequence Analysis, DNA; D037521:Virulence Factors / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D037521:Virulence Factors; C048795:AmpC beta-lactamases; D001618:beta-Lactamases