Prevalence of toxigenic and invasive strains of Escherichia coli in a hospital population. 
The pathogenesis of gastrointestinal infections caused by Escherichia coli has been attributed to the ability of some strains to produce exotoxins (enterotoxins) or to invade the intestinal mucosa directly.  To investigate the possible role of invasiveness and of production of toxin in the pathogenesis of nonenteric E. coli infections, we studied E. coli isolated from 152 patients with urinary tract infections, bacteremia, or both.  None of the isolates from urine or blood exhibited invasiveness in the guinea pig eye or produced toxin in tissue culture or in infant mice; only one patient was a gastrointestinal carrier of toxin-producing E. coli.  We concluded that, in the population of this study, production of toxin and invasiveness were not important in the pathogenesis of most urinary tract infections or bacteremia caused by E. coli, and that gastrointestinal colonization with such organisms was uncommon.