Native Microbial Colonization of Drosophila melanogaster and Its Use as a Model of Enterococcus faecalis Pathogenesis

Abstract

Enterococci are commensal organisms of the gastrointestinal (GI) tracts of a broad range of mammalian and insect hosts, but they are also leading causes of nosocomial infection. Little is known about the ecological role of enterococci in the GI tract consortia. To develop a tractable model for studying the roles of these organisms as commensals and pathogens, we characterized the Drosophila melanogaster microflora and examined the occurrence of enterococci in the gastrointestinal consortium of Drosophila. In a survey of laboratory-reared Drosophila and wild-captured flies, we found that Drosophila was naturally colonized by representatives of five bacterial phyla. Among these organisms were several species of enterococci, including Enterococcus faecalis, Enterococcus faecium, Enterococcus gallinaraum, and Enterococcus durans, as well as a previously detected but uncultured Enterococcus species. Drosophila could be cured of enterococcal carriage by antibiotic treatment and could be reassociated with laboratory strains. High-level colonization by a well-characterized strain expressing the enterococcal cytolysin was found to be detrimental to Drosophila compared to the effect of an isogenic, noncytolytic control. The anatomical distribution of enterococci in the Drosophila GI tract was determined by immunohistochemical staining of thin sections of naturally colonized and reassociated flies.Enterococci are among the most common causes of hospitalacquired infections (24, 38). The enterococci that cause these infections are often resistant to multiple antibiotics and, with increasing frequency, to all antibiotics (38). It was recently proposed (30) that nosocomial enterococcal infections may be the result of a two-step process: asymptomatic colonization and amplification within the gastrointestinal (GI) tract of virulent, antibiotic-resistant enterococcal strains, followed by infection of extraintestinal sites, such as the bloodstream, urinary tract, or a surgical wound. However, little is known about the mechanisms used by enterococci to colonize the GI tracts of either healthy individuals or hospitalized patients. Studies of mammalian GI tract colonization and the transition to infection are exceedingly complex because of the number of variables involved. An estimated 500 taxa are represented among the bacterial species in the consortium in the human colon (23,71,72), and species representation in this consortium varies by age, diet, and genetics. This complexity is further compounded by the health status of the host and by antimicrobial therapy (72).Enterococci are present naturally in the GI tracts of insects (8,11,49,50,70), reptiles (55), humans, and other mammals (1,38,55,59). Enterococci are minority members of the human GI tract consortium, comprising up to 1% of the adult microflora (65). Enterococcus faecalis and Enterococcus faecium are the two species most commonly detected in the human bowel (27,59,72), while Enterococcus durans occurs in a small percentage of adults (72). Martin and Mundt (50) recognize...

The inconstant gut microbiota of Drosophila species revealed by 16S rRNA gene analysis

“…In this study, individual microbial taxa were not generally found to be shared universally, either within or among drosophilid species in laboratory conditions. In particular, the data do not substantiate the common bacterial taxa found by Cox and Gilmore (2007) across laboratory and field conditions for one species, D. melanogaster. Our results complement and extend the research of Chandler et al (2011), in which shallow sampling with Sanger sequencing failed to yield a common subset of bacterial OTUs among field samples of multiple Drosophila species.…”

“…An important caveat to our understanding is whether the gut microbiota includes a common phylogenetic subset. Cox and Gilmore (2007) noted three taxa, Acetobacter aceti, A. pasteurianus and Enterococcus faecalis, in two laboratory strains and one wild population, but Corby-Harris et al (2007) described 74 taxa that were 'unevenly spread' among wild populations of D. melanogaster. Chandler et al (2011) reported that members of Enterobacteriaceae and Lactobacillales are very widely distributed, but apparently not universal, across 20 populations of multiple species.…”

“…The gut microbiota in these insects has been reported to include Proteobacteria (especially Acetobacteraceae and Enterobacteriaceae) and Firmicutes of the order Lactobacillales (notably Lactobacillus and Enterococcus species). Despite regional variation in conditions (pH, redox potential and so on) in the gut (Shanbhag and Tripathi, 2009), bacteria occur in the crop, midgut and hindgut, with densities up to 10 6 cells per fly (Corby-Harris et al, 2007;Cox and Gilmore, 2007;Ren et al, 2007;Roh et al, 2008;Sharon et al, 2010;Chandler et al, 2011;Storelli et al, 2011;Wong et al, 2011). Elimination of the gut bacteria can result in delayed larval development, altered lifespan and changes in nutrient allocation attributable to disruption in insect insulin signaling (Brummel et al, 2004;Shin et al, 2011;Storelli et al, 2011;Ridley et al, 2012).…”

Evidence for a core gut microbiota in the zebrafish

“…Analysis of wild and domesticated mice (Wilson et al, 2006), turkeys (Scupham et al, 2008), parrots (Xenoulis et al, 2010), fruitflies (Cox and Gilmore, 2007) and hydra (Fraune and Bosch, 2007) indicate that members of the same species tend to possess gut bacterial communities of similar taxonomic composition at the phylum or class level regardless of domestication status, with some differences between wild and domestic individuals emerging at shallower phylogenetic resolution. These previous studies have revealed varying effects of domestication on gut bacterial diversity, with increased diversity in wild mice (Wilson et al, 2006) and fruitflies (Cox and Gilmore, 2007) compared with domesticated controls, and decreased diversity in wild versus domesticated parrots (Xenoulis et al, 2010). Our clone library sequencing and pyrosequencing of the zebrafish intestinal microbiota revealed variation between recently caught and domesticated zebrafish, however, the scale of these variations were no larger than those observed between or within different zebrafish lab facilities (Figures 2, 4, and Supplementary Figure S1).…”

Integrating nutrition and immunology: A new frontier

“…Gut microbes also play a role in invertebrate biology (Dillon and Dillon, 2003) and digestive process [Brune, 2011 [Lundgren, 2010, and recently the composition of microbe gut populations has been described in a variety of insect species, including bees (Jeyaprakash et al, 2003;Mohr and Tebbe, 2006), beetles (Egert et al, 2005;Lehman et al, 2009;Nardi et al, 2006;Zhang and Jackson, 2008), flies (Cox and Gilmore, 2007;Ren et al, 2007;Ryu et al, 2008;Shin et al, 2011;Wong et al, 2011), lepidopterans (Pauchet et al, 2010;Xiang et al, 2006) and termites (Hongoh et al, 2003). In Drosophila, the microbiome regulates host metabolic homeostatic and developmental programs by modulating the insulin/insulin-like growth factor (Shin et al, 2011).…”