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Title: Temporospatial fate of bacteria and immune effector expression in house flies (Musca domestica L.) fed GFP-E. coli O157:H7

Author
item FLEMING, ADAM - Georgia Southern University
item KUMAR, NAVEEN - Georgia Southern University
item JOYNER, CHESTER - Emory University
item REYNOLDS, AMANDA - Georgia Southern University
item Nayduch, Dana

Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2013
Publication Date: 12/1/2014
Citation: Fleming, A., Kumar, N., Joyner, C.J., Reynolds, A., Nayduch, D. 2014. Temporospatial fate of bacteria and immune effector expression in house flies (Musca domestica L.) fed GFP-E. coli O157:H7. Medical and Veterinary Entomology. 28, 364–371. DOI: 10.1111/mve.12056

Interpretive Summary: House flies harbor and transmit a variety of human gastrointestinal pathogens including E. coli O157:H7. Interactions between ingested bacteria and the fly gut directly impact bacterial persistence, survival and ultimately their ability to transmit pathogens to humans and other animals. In this study, we assessed the fate of GFP-expressing E. coli O157:H7 (GFP-ECO157) in house flies along with fly antimicrobial responses for 12 h post-ingestion, in order to get a better idea of the location and persistence of bacteria harbored inside of flies as well as their defense responses to bacteria. In flies fed GFP-ECO157, culture and microscopy revealed a steady decrease in bacterial load over 12 h, which was likely attributable to the combined effects of immobilization, lysis and excretion by peristalsis. However, viable bacteria were observed in both the crop and rectum of flies, which implies that house flies can putatively transmit this pathogen in excreta. Quantitative gene expression analysis of antimicrobial peptides (AMP) and the bacteria-digesting enzyme lysozyme showed minimal upregulation in both the gut and carcass of house flies fed GFP-ECO157. However, these genes were upregulated in fly heads and salivary glands, and effector proteins were detected in the gut of some flies. Collectively, these data indicate that house flies can serve as reservoirs of E. coli O157:H7 for up to 12 h, and factors in addition to AMPs and lysozyme may contribute to bacteria destruction in the gut.

Technical Abstract: House flies (Diptera: Muscidae; Musca domestica L.) harbor and transmit a variety of human enteropathogens including E. coli O157:H7. Interactions between ingested bacteria and the fly gut directly impact bacterial persistence, survival and ultimately fly vector competence. We assessed the temporospatial fate of GFP-E. coli O157:H7 (GFP-ECO157) in house flies along with fly antimicrobial responses for 12 h post-ingestion. In flies fed GFP-ECO157, culture and microscopy revealed a steady decrease in bacterial load over 12 h, which was likely attributable to the combined effects of immobilization within the peritrophic matrix, lysis and peristaltic excretion. However, flies can putatively transmit this pathogen in excreta because viable bacteria were observed in the crop and rectum. qRT-PCR analysis of antimicrobial peptides (AMP) and lysozyme expression showed minimal upregulation in both the gut and carcass of house flies fed GFP-ECO157. However, these genes were upregulated in fly heads and salivary glands, and effector proteins were detected in the gut of some flies. Collectively, these data indicate that house flies can serve as reservoirs of E. coli O157:H7 for up to 12 h, and factors in addition to AMPs and lysozyme may contribute to bacteria destruction in the gut.