Procurement and persistence of GFP-expressing Escherichia coli and Salmonella typhimurium in male and female house flies exposed to cattle manure

House flies, Musca domestica L., are vectors of pathogenic bacteria that are acquired from fly natural developmental sites (e.g. decomposing matter and animal manure) and potentially transferred to surrounding environments, including residential areas, via contaminated body parts or excreta. Unlike male house flies, females seek out microbe-rich environments for oviposition which could result in more frequent visits to manure. The objective of this project was to determine if there is an effect of fly sex and exposure time on bacterial acquisition from manure. Mated 7-9 day old house flies were separated into two treatment groups (n=25, reps=4): (1) males only and (2) females only. Flies were exposed to autoclaved manure inoculated with either GFP-expressing E. coli or Salmonella sp. (10⁵ CFU/g), and bacterial persistence was determined at 3 time points (4, 12, 24h post-exposure) from manure and individual flies. As a follow up, flies were given a choice between inoculated manure and 10% sucrose in each treatment to determine if manure was being utilized as a food source.  It was expected that abundance of recoverable bacteria in flies would increase with length of exposure time as flies would utilize manure for nutrients. Additionally, we predicted that female flies would have higher bacterial loads due to oviposition behavior which could increase fly contact with manure. A better understanding of the potential of house flies to acquire bacteria from manure and the amount of viable bacteria flies can harbor over time is important in informing mitigation and management strategies on farms.