Resumo

Escherichia coli are the facultative Gram-negative rods most abundant in the intestinal flora of warm-blooded animals. It colonizes the human-beings right after their birth and is kept as a commensal for their whole life. So far there are no comprehensive studies on the intensity of intestinal colonization of healthy individuals by E. coli strains potentially virulent to extra-intestinal sites (ExPEC). This work studied the incidence of these strains as well as their antimicrobial resistance profile, during the period of 2009-10, in the stool specimens of 91 healthy individuals resident in São Paulo, Brazil. The participants were zero to 85 years old, from both genders, and did not suffered from gastrointestinal disorders or took antimicrobial drugs in the 30 days preceding the feces collection. Five isolated E. coli colonies from each stool sample were characterized according their phylogenetic origin (multiplex PCR), and presence of 17 genetic markers associated to ExPEC virulence factors (FVs) (colony hybridization). They were classified as ExPEC if contained at least two of five virulence determinants shown to be related to the lethal potential in a sepsis animal-model. Their susceptibility profile to eight antimicrobial drugs commonly used in hospital, community or veterinary settings was determined. Only those colonies presenting unique phylogenetic and virulence profiles among the five isolates of each individual were considered for further analysis, resulting in a total of 201 colonies. The phylo-groups A and D were predominant (37.3% and 25%, respectively). All the strains possessed one to 15 FVs being the most frequent: ompA (100%), fimA (87.6%), ompT (43%), and irp2 (40%). The frequency of resistant strains ranged from 0.5% to 22.4% depending on the drug. Approximately, 20% of the strains presented high virulence potential and were isolated from 30% of the studied population. These strains presented the following characteristics: all classified as ExPEC (assumed to be lethal in the animal model), most were from phylo-group B2 with high virulence-factor score (10.6), and resistance to three or more of the tested antimicrobials (50% of the strains). These data show that the intestinal tract of a significant percentage of the healthy population studied constitutes a reservoir of extra-intestinal pathogenic E. coli displaying high virulence potential and high antimicrobial resistance.