Abundance and accumulation of Escherichia coli and Salmonella Typhimurium procured by male and female house flies (Diptera: Muscidae) exposed to cattle manure

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

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2016
Publication Date: 12/29/2016
Citation: Thomson, J., Yeater, K.M., Zurek, L., Nayduch, D. 2016. Abundance and accumulation of Escherichia coli and Salmonella Typhimurium procured by male and female house flies (Diptera: Muscidae) exposed to cattle manure. Annals of the Entomological Society of America. 110:37-44.

Interpretive Summary: House flies develop within and feed upon microbe-rich substrates such as manure, acquiring and potentially disseminating pathogenic bacteria. Because adult female flies frequent manure due to oviposition or nutrition requirements, we hypothesized females would contact manure more than males even in the presence of additional food sources (e.g. sugar), resulting in measurable differences in bacterial load between sexes. House fly acquisition of bacteria from manure inoculated with GFP-expressing E. coli or Salmonella sp. was examined for both sexes over 24 h in assays where (1) inoculated manure was the only food source and (2) both inoculated manure and sugar water were provided. We conducted assays with mated male and female flies separately to determine sex-specific effects on bacterial acquisition. At three time points, 4, 12 and 24 h post-exposure, we collected a 1 g sample of manure and 5 flies for bacterial culture and enumeration. The amount of bacteria cultured from manure increased in the S. Typhimurium assays, but not the E. coli assays. In flies, the amount of bacteria only increased over time in both S. Typhimurium assays. In all assays, female flies always harbored more bacteria than males, irrespective of bacteria or food types (manure-only, manure-sugar). However, the difference in bacteria amounts were only statistically significant at early time points (4 and/or 12 h after exposure). In the E. coli manure-sugar assays, male and female CFU abundance differed only at 4 h post-exposure, while CFU abundance differed at both 4 and 12 h in both S. Typhimurium assays. In a separate set of experiments, we exposed flies to manure in the same assays as above, and dissected them to view the appearance of food in the digestive tract. Observations of digestive tracts of flies from manure-sugar assays supported these initial differences we saw in bacterial culture, especially at 4 h, where the guts of female flies contained primarily manure and fly food, while male flies contained primarily sugar water. Identifying the effect that fly sex may play in house fly acquisition and carriage of bacteria from manure can help in asssessing risk of pathogen transmission by flies on farms.

Technical Abstract: House flies, Musca domestica L. develop within and feed upon microbe-rich substrates such as manure, acquiring and potentially disseminating pathogenic bacteria. Because adult female flies frequent manure due to oviposition or nutrition requirements, we hypothesized females would contact manure more than males even in the presence of additional food sources (e.g. sugar), resulting in measurable differences in bacterial load between sexes. House fly acquisition of bacteria from manure inoculated with GFP-expressing E. coli or Salmonella sp. was examined for both sexes over 24 h in assays where (1) inoculated manure was the only food source and (2) both inoculated manure and sugar water were provided. We conducted assays with mated male and female flies separately to determine sex-specific effects on bacterial acquisition. Over 24 h, bacterial abundance increased in manure inoculated with S. Typhimurium, but not E. coli. In flies, bacterial abundance increased within sex only in S. Typhimurium assays. Overall, female flies harbored more bacteria than males; however, differences in abundance were only significant at early time points. In the E. coli manure-sugar assays, male and female CFU abundance differed only at 4 h, while CFU abundance differed at both 4 and 12 h in all S. Typhimurium assays. Fly digestive tract observations from manure-sugar assays supported these initial differences especially at 4 h where females contained manure and fly food, while males contained only sugar water. Identifying sex-specific effects on house fly acquisition and carriage of bacteria from manure facilitates risk assessment of pathogen transmission on farms.