Persistence of GFP-expressing E. coli in house flies exposed to cattle manure

House flies, Musca domestica L., are potential vectors for various pathogens that can be acquired from their natural breeding sites (decomposing matter and manure) and transferred to other nearby or surrounding environments. Flies disseminate bacteria from their contaminated body parts and through regurgitation or defecation of ingested materials. The objective of this project was to see if there is an effect of fly sex and exposure time on bacterial acquisition from manure. We examined the persistence of GFP-expressing E. coli in male and female house flies acquired by exposure to inoculated cattle manure. Five day old house flies were mated for a day and then separated into three treatment groups: (1) males and females mixed, (2) males only, (3) females only. Flies were exposed to sterilized manure inoculated with 10⁴ CFU/ml GFP-E. coli and interacted freely. Samples of flies and manure were taken at 4 time points for selective culturing over a 24 h period. It was expected that bacterial enumeration would increase with length of exposure to manure due to there being no other available nutrient sources. Additionally, mixed-sex flies would have higher bacterial loads than single sex flies due to mating interactions and females would have higher bacterial loads overall due to innate female oviposition behavior around manure. This project lends insight into potential for house flies to acquire bacteria from manure and determines amount of viable bacteria flies can harbor and vector over time, which could be important in developing mitigation and management strategies on farms.