Commensal Escherichia coli – a hidden threat of extraintestinal infections

The human gut is the main reservoir of extraintestinal pathogenic Escherichia coli (ExPEC). These strains are part of the microbiota of healthy individuals, where they coexist with commensal E. coli, but differ from them by the presence of virulence genes and, as a rule, by belonging to phylogenetic group B2. Objective. To characterize the population structure of commensal E. coli strains and to assess the risk of developing extraintestinal diseases. Materials and methods. Using polymerase chain reaction, we examined biological properties indicative of pathogenicity (virulence genes associated with adhesion, toxin production, and persistence) and phylogenetic group affiliation in 490 E. coli strains isolated from the feces of adult residents of Saint Petersburg without signs of acute or chronic gastrointestinal diseases. Results. E. coli strains most frequently belonged to phylogenetic groups A (62.7%) and B1 (3.2%). Groups B2 and D typically associated with ExPEC accounted for 22.4% and 11.6% of isolates, respectively. A high potential for causing urinary tract infections was identified in 38.7% of strains, including pathogens capable of causing meningitis and sepsis (22.8%). Analysis of genetic determinants associated with extraintestinal pathogenicity revealed considerable variation. A high frequency of key ExPEC virulence factors was characteristic of strains belonging to phylogenetic group B2. Conclusion. The human gut microbiota serves as an endogenous reservoir of pathogenic ExPEC potential uropathogens, including causative agents of secondary meningitis and sepsis. Key words: gut microbiota, Escherichia coli, phylogenetic groups, commensalism, virulence genes, pathogenic potential, ExPEC