Phylogenetic group B2 Escherichia coli strains from the bowel microbiota of Pakistani infants carry few virulence genes and lack the capacity for long-term persistence.

Escherichia coli strains of phylogenetic group B2 obtained from Western human hosts are enriched in virulence-associated genes and have a superior capacity to persist in the colonic microbiota. Here, E . coli strains from 22 infants born in Pakistan whose rectal flora was sampled regularly over the first 6 months of life were examined. B2 strains did not carry the virulence-associated genes sfaD/E, papC, neuB or hlyA more often than strains of other phylogenetic groups. B2 origin was not associated with persistence in the bowel microbiota. As compared with B2 strains from Swedish infants, Pakistani B2 strains carried significantly less often the virulence genes fimH (p 0.04), papC (p 0.02), papG class III (p 0.01), sfaD/E (p < or =0.0001), neuB (p < or =0.0001), and hlyA (p 0.005), and also the high-pathogenicity island (p < or =0.0001). A minority of Pakistani B2 strains belonged to recognized uropathogenic O-groups, which are common among 'Western' B2 strains. Thus, extra-intestinal pathogenicity may be the foremost characteristic of B2 strains colonizing Western populations.