In vitro and in vivo bacteriolytic activities of Escherichia coli phages: implications for phage therapy.

Four T4-like coliphages with broad host ranges for diarrhea-associated Escherichia coli serotypes were isolated from stool specimens from pediatric diarrhea patients and from environmental water samples. All four phages showed a highly efficient gastrointestinal passage in adult mice when added to drinking water. Viable phages were recovered from the feces in a dose-dependent way. The minimal oral dose for consistent fecal recovery was as low as 10(3) PFU of phage per ml of drinking water. In conventional mice, the orally applied phage remained restricted to the gut lumen, and as expected for a noninvasive phage, no histopathological changes of the gut mucosa were detected in the phage-exposed animals. E. coli strains recently introduced into the intestines of conventional mice and traced as ampicillin-resistant colonies were efficiently lysed in vivo by phage added to the drinking water. Likewise, an in vitro phage-susceptible E. coli strain freshly inoculated into axenic mice was lysed in vivo by an orally applied phage, while an in vitro-resistant E. coli strain was not lysed. In contrast, the normal E. coli gut flora of conventional mice was only minimally affected by oral phage application despite the fact that in vitro the majority of the murine intestinal E. coli colonies were susceptible to the given phage cocktail. Apparently, the resident E. coli gut flora is physically or physiologically protected against phage infection.