Diversity of bacteria associated with the house fly (Dipt.: Musca domestica L.) and horizontal gene transfer among bacteria in the house fly gut

The microbial diversity of the gastrointestinal track in animals is determined by commensal and symbiotic relationships and interactions between microbes, their animal hosts, and the external environment. Although the significance of house flies as vectors of pathogens has been acknowledged, an intensive study of the bacterial flora associated with the house fly gut environment has heretofore been lacking. Quantifying gut bacterial biodiversity is of particular interest for an insect vector of pathogens associated with food borne diseases. Furthermore, the significance of the house fly gut as a potential site for the emergence of new bacterial pathogens through genetic exchange mechanisms has not been explored.; This study determined that horizontal gene transfer among strains of Escherichia coli can occur in the fly gut. Plasmid-born antibiotic resistance genes and bacteriophage-born Shiga toxin genes moved horizontally between donor and recipient strains in this environment. These findings suggest that the house fly gastrointestinal tract is a favorable environment for the evolution and emergence of new pathogens, when acquisition of genes contributing to virulence is a component of the process.; The bacterial diversity of the house fly gut was studied by using two culture independent approaches. A Terminal Fragment Length Polymorphism (T-RFLP) analysis was used to quantify diversity and compare the microbial community found in the gut and exoskeleton of house flies. House fly gut harbored a complex microbiota, whereas the exoskeleton was less diverse and more variable, reflecting environmental pressures. There was no evidence from this analysis to justify that use of antibiotics in dairy farms where flies were sampled had a significant effect on house fly bacterial community structures in the gut or exterior surface. A comparative analysis involving construction of bacterial 16S rDNA sequence libraries of the house fly gut and cow fecal bacterial communities showed that house fly gut community was more diverse (55 genera) than the cow fecal community (27 genera), but forty percent of the clones classified to genus (16 genera) were common to both communities. The genera Pseudomonas, Janthinobacterium, Clostridium, and Acinetobacter were especially common in both communities. Within the house fly gut, several potentially pathogenic bacterial groups were evident, including Enterobacter, Enterococcus, Shigella, and Pantoea. However, both communities were highly uneven with a few dominant taxa and many uncommon taxa; a richness estimator predicted 36 and 79 genera for the fecal and house fly gut communities, respectively.