Variation in frequency of the virulence-factor gene in Escherichia coli clones colonizing the stools and urinary tracts of healthy prepubertal girls.

To provide information on virulence expression of Escherichia coli in healthy hosts, stool, periurethral, and urine samples were collected weekly from healthy 3-6-year-old girls who lived in a small rural community. Dominant and nondominant clones were defined in stool specimens, and the expression of virulence factors was determined. We found that healthy girls commonly shared dominant clones. P adhesin, hemolysin, and type I adhesin were commonly found in clones in the stool and in clones in the urinary tract. In addition, expression of virulence factors, among both dominant and nondominant clones in the stool, changed from week to week. The presence of P adhesin was a marker for the persistence of a dominant clone in the stool and was associated with an increased likelihood that a nondominant clone would be detected in the urinary tract. Type I adhesin was ubiquitous among stool strains, with orientation of the fimbrial switch being both in the "off" position and in both the "on" and "off" positions. In summary, the intestinal flora of healthy girls is complex, with frequent changes in virulence expression.