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

Authors: THOMSON, JESSICA - Kansas State University; Yeater, Kathleen; ZUREK, LUDEK - Kansas State University; Nayduch, Dana

Submitted to: International Congress of Entomology
Publication Type: Proceedings
Publication Acceptance Date: 1/27/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: House flies develop in and feed upon microbe-rich substrates such as manure, acquiring and potentially disseminating pathogenic bacteria. Due to their life-long association with these substrates, as well as their high mobility and gregariousness, adult house flies likely vector pathogenic bacteria such as E. coli and Salmonella. Adult female house flies require protein for egg development, and ingest animal manure and other secretions to meet this nutritional need. Female flies also visit manure as potential sites for egg laying. Thus, both of these activities may lead to more frequent visits to manure by female flies than by male flies, resulting in differences in procurement and abundance of bacteria acquired from manure. We hypothesized that even in the presence of additional food sources (e.g. sugar), there would be measurable differences in bacterial load between male and female house flies. Our objectives were to determine if male and female house flies differ in the amount of bacteria (E. coli and Salmonella) acquired from manure over time when (1) manure was the only food source and (2) manure and sugar were both available. We found that female house flies always harbored more bacteria than male house flies, and that this was statistically significant at early time points (4 and 12 h post exposure to manure) in all assays except those were E. coli-inoculated manure was the only food source. Furthermore, Salmonella abundance increased in both male and female flies both when manure was the only source of food/bacteria and when manure and sterile sugar were both present. Female flies also more frequently had bacteria (acquired from manure) on their surfaces. Taken together, our results suggest that female flies may have a higher potential to harbor and disseminate bacteria acquired from manure. As result, fly sex should be considered risk assessment and pest management strategies, especially on farms.

Technical Abstract: Introduction: Adult house flies, Musca domestica L., are associated with animal manure and other microbe-rich substrates. Consequently, both sexes can acquire and potentially disseminate pathogenic bacteria to surrounding environments, including residential areas, via contaminated body parts and/or excreta. We hypothesized that because of oviposition, females contact manure sites more frequently than males and subsequently would carry higher bacterial loads than males. Therefore, we examined bacterial acquisition from manure in both sexes of house flies over time and determined whether bacterial load differed when an additional sugar source was present. Methods: Mated 7-9 d old male or female adults (n = 25 each, 4 replicates) were exposed to (1) autoclaved manure inoculated with either GFP-expressing Escherichia coli or Salmonella Typhimurium (105 CFU/g) or (2) autoclaved manure (inoculated with bacteria, as above) and a droplet (60 µl) of 10% sucrose. Over 24 h, the abundance of bacteria in manure and flies was assessed by culture. Results/Conclusion: In the first study, bacterial abundance in both sexes increased over time irrespective of bacterial species present (P = 0.037). However, in the second study, abundance of S. Typhimurium increased significantly over time in males and females (P < 0.0001), while that of E. coli did not (P > 0.05). Moreover, females had higher bacterial loads than males in both studies (P = 0.019). A better understanding of the potential of house flies to acquire and harbor bacteria from manure over time is important to inform fly management strategies on farms.