Factors affecting the excretion of GFP Salmonella enterica serovar typhimurium by adult house flies (Diptera: Muscidae; Musca domestica L.)

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

Submitted to: Entomological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/8/2017
Publication Date: 11/7/2017
Citation: Nayduch, D., Zurek, K., Thomson, J., Yeater, K.M. 2017. Factors affecting the excretion of GFP Salmonella enterica serovar typhimurium by adult house flies (Diptera: Muscidae; Musca domestica L.) . Entomological Society of America Proceedings. https://esa.confex.com/esa/2017/meetingapp.cgi/Paper/121995.

Interpretive Summary: House flies harbor and disseminate food-borne pathogens. Salmonella Typhimurium (S. Typhimurium) is a zoonotic pathogen shed by livestock that causes gastroenteritis in humans. We previously demonstrated that GFP-S. Typhimurium fed to house flies persist in the digestive for 24h. The excretion dynamics of S. Typhimurium from infected flies is unknown yet essential in assessing transmission potential. Here, we examined the excretion of GFP S. Typhimurium from individual house flies from 6-12h post-ingestion. Individual male and female house flies were fed either sterile Luria-Bertani broth (LB, controls), or LB containing “high” (~100,000 cells or “low” (~10,000 cells) dose cultures of bacteria. Excretion events (vomit or defecation) were recorded for each fly, and excreta droplets were cultured from flies receiving bacteria treatments to enumerate the amount of bacteria within those droplets. There was no difference in the number of excretion events across control and treatment groups. There was no overall effect of treatment on the proportion of infected droplets shed by flies, however there was a sex effect in the low dose treatment, where 85% of droplets from low-dose males were positive for bacteria, while only 36% were positive from low-dose females. The amount of bacteria excreted in each droplet was affected by sex in the high dose treatment. High dose male flies excreted more bacterial cells per droplet than low dose (mean number of bacterial cells excreted per droplet: high=792; low=280), but the inverse effect was observed in females (mean number of bacterial cells excreted per droplet: high=152, low=374). Overall, irrespective of sex, low dose flies excreted a greater dose-adjusted amount of bacteria (cells per droplet/cells fed to each fly) than high dose flies. This study demonstrates that the amount of bacteria a fly ingests as well as the sex of the fly both can influence the risk of house fly transmission of pathogens.

Technical Abstract: House flies harbor and disseminate food-borne pathogens. Salmonella Typhimurium (S. Typhimurium) is a zoonotic pathogen shed by livestock that causes gastroenteritis in humans. We previously demonstrated that GFP-S. Typhimurium fed to house flies persist in the digestive for 24h. The excretion dynamics of S. Typhimurium from infected flies is unknown yet essential in assessing transmission potential. Here, we examined the excretion of GFP S. Typhimurium from individual house flies from 6-12h post-ingestion. Individual male and female house flies (n=3/sex/treatment; two replicates) were fed either sterile Luria-Bertani broth (controls), or LB containing “high” (~105 CFU) or “low” (~104 CFU) dose cultures of bacteria (treatments). Excretion events were recorded for each fly, and excreta droplets were cultured from treatments to enumerate CFU. There was no difference in the number of excretion events across control and treatment groups. There was no overall effect of treatment on the proportion of infected droplets shed by flies, however there was a sex effect in the low dose treatment (proportions: males, 0.85; females, 0.36; P=0.0011). The CFU/droplet excreted by flies was affected by sex in the high dose treatment (P=0.0005). Interestingly, high dose male flies excreted more CFU/droplet than low dose (high=792; low=280; p=0.016), and the inverse effect was observed in females (high=152, low=374; p=0.0084). Overall, irrespective of sex, low dose flies excreted a greater dose-adjusted CFU (CFU droplet/CFU fed) than high dose flies (Low=0.88, High=0.28; P=0.009). This study demonstrates that bacterial abundance and fly sex can influence the risk of house fly transmission of pathogens.