| Enterococci are commensal organisms of the gastrointestinal tract of a broad range of mammalian and insect hosts, but are also leading causes of nosocomial infection. Little is known about the ecological role of enterococci in the GI tract consortium. To develop a tractable model for the study of their roles as commensals and pathogens, we characterized the Drosophila microflora, and examined the occurrence of enterococci in the gastrointestinal consortium of Drosophila. In a survey of laboratory reared Drosophila and wild-captured flies, Drosophila was found to be naturally colonized by representatives of 5 bacterial phyla. Among these were several species of enterococci including E. faecalis, E. faecium, E. gallinaraum, E. durans, as well as a previously detected but uncultured Enterococcus species. Drosophila could be cured of enterococcal carriage by antibiotic treatment, and reassociated with laboratory strains. High-level colonization by a well-characterized strain expressing the enterococcal cytolysin was found to be detrimental to wild-type Drosophila in comparison to an isogenic, non-cytolysic control. Drosophila Toll loss-of-function mutants, deficient in the ability to mount an innate immune defense against Gram-positive infections, were found to be less susceptible to the effects of the enterococcal cytolysin, and consistently colonized to lower levels (CFU/fly). The anatomical distribution of enterococci within the Drosophila GI tract was determined by immunohistochemical staining of thin-sections of naturally colonized and reassociated flies. |
