Phylogenetic Groups and Pathogenicity Island Markers in Fecal Escherichia coli Isolates from Asymptomatic Humans in China

The study of phylogenetic groups and pathogenicity island (PAI) markers in commensal Escherichia coli strains from asymptomatic Chinese people showed that group A strains are the most common and that nearly half of all fecal strains which were randomly selected harbor PAIs.Escherichia coli is a well-diversified commensal species in the intestine of healthy humans but also includes intestinal or extraintestinal pathogens. It has been reported that pathogenic E. coli may be derived from fecal strains by acquisition of virulence determinants (11). The relationship between the E. coli genetic background and the acquisition of virulence factors is now better understood (1, 5). Extraintestinal E. coli strains may harbor several virulence factors, such as adhesins, fimbriae, and hemolysin, which can contribute to bacterial pathogenesis. These traits are usually encoded on pathogenicity islands (PAIs), which have been studied in pathogenic E. coli previously (15). The E. coli population includes 4 major phylogroups (A, B₁, B₂, and D) (2). Pathogenic strains belong mainly to groups B₂ and D, while most fecal isolates belong to groups A and B₁. Strains of groups B₂ and D often carry virulence factors that are lacking in group A and B₁ strains (3, 9, 13).In this study, we examined the distribution of phylogroups and the prevalence of PAIs in commensal E. coli strains isolated from asymptomatic persons in one region of China.