Phylogenetic groups and virulence factors in pathogenic and commensal strains of Escherichia coli and their association with blaCTX-M.

We compared the distribution of phylogenetic groups and nine virulence factors among the pathogenic (isolated from blood and urine) and commensal (isolated from feces of healthy individuals) strains of Escherichia coli, and also compared the occurrence of virulence factors according to the production of (bla)(CTX-M) among the pathogenic strains. A total of 550 non-duplicate E. coli isolates (145 from blood, 200 from urine, 205 from feces) were collected. Phylogenetic grouping and virulence genotyping were done by PCR for all isolates. For pathogenic strains, antimicrobial susceptibility tests and PCR for (bla)(CTX-M) were performed. The distribution of phylogenetic groups was similar between isolates from blood and urine: B2 (44.8%; 58.5%, respectively) > D (29.0%; 23.0%, respectively) > A (18.6%; 9.5%, respectively) > B1 (7.6% and 9.0%, respectively). Phylogenetic groups B2 and D were also frequent (22.9% and 21.0%, respectively) among isolates from feces. The prevalence of all virulence factors except S fimbrial adhesion was significantly higher in pathogenic strains than in commensal strains and they were most frequent in phylogenetic group B2. α-Haemolysin, yersiniabactin receptor, serum resistance-associated outer membrane protein (traT), and aerobactin receptor (iutA) were found to be independent predictors for pathogenicity, and of them, iutA and traT were significantly more common in (bla)(CTX-M-1 group) and (bla)(CTX-M-9 group,) respectively. Considering the possibility that these virulence genes, together with antimicrobial resistance genes, can spread to other strains, further study and ongoing surveillance seem to be required.