Temporospatial fate of bacteria and immune effector expression in house flies fed GFP-Escherichia coli O157:H7.

The house fly Musca domestica L. (Diptera: Muscidae) harbours and transmits a variety of human enteropathogens including Escherichia coli (Enterobacteriales: Enterobacteriaceae) 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 green fluorescent protein (GFP)-expressing E. coli O157:H7 (GFP-ECO157) in house flies along with fly antimicrobial responses up to 12 h post-ingestion. In flies fed GFP-ECO157, culture and microscopy revealed a steady decrease in bacterial load over 12 h, which is likely to be 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 intact bacteria were observed in the crop and rectum. Quantitative reverse-transcriptase polymerase chain reaction analysis of antimicrobial peptides (AMPs) and lysozyme gene 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 in 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. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.