Commensal Escherichia coli isolates are phylogenetically distributed amonggeographically distinct human populations

An intraspecies phylogenetic grouping of 168 human commensal Escherichia co li strains isolated from the stools of three geographically distinct human populations (France, Croatia, Mall) was generated by tripler PCR, The distr ibutions of seven known extraintestinal virulence determinants (ibeA, pap, sfalfoc, afa, hly. cnf1, aer) were also determined by PCR, The data from th e three populations were compiled. which showed that strains from phylogene tic groups A (40 %) and B1 (34%) were the most common, followed by phylogen etic group D strains (15%). Strains of the phylogenetic group B2 were rare (11%), However, a significant specific distribution for strains of groups A , B1 and B2 within each population was observed, which may indicate the inf luence of (i) geographic/climatic conditions, (ii) dietary factors and/or t he use of antibiotics or (iii) host genetic factors on the commensal flora. the use of antibiotics or (iii) host genetic factors on the commensal flor a. Virulence determinants were rarely detected, with only 25.6 % of the str ains harbouring at least one of the virulence genes tested. The strains wit h virulence factors most frequently belonged to phylogenetic group B2, The commensal strains of phylogenetic groups A, B1 and D had fewer virulence de terminants than pathogenic strains of the corresponding groups when these d ata were compared with those for previous collections of virulent extrainte stinal infection strains studied using the same approach. However, the viru lence patterns of commensal and pathogenic B2 phylogenetic group strains we re the same. The data thus suggest that strains of the A, B1 and a phylogen etic groups predominate in the gut flora and that these strains must acquir e virulence factors to become pathogenic. In contrast, commensal phylogenet ic group B2 strains are rare but appear to be potentially virulent.