Environmental and sex effects on bacterial carriage by adult house flies (Musca domestica L.)

Authors: NEUPANE, SARASWOTI - Kansas State University; WHITE, KOTIE - Kansas State University; THOMSON, JESSICA - Kansas State University; ZUREK, LUDEK - Mendel University; Nayduch, Dana

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2020
Publication Date: 6/28/2020
Citation: Neupane, S., White, K., Thomson, J.L., Zurek, L., Nayduch, D. 2020. Environmental and sex effects on bacterial carriage by adult house flies (Musca domestica L.). Insects. 11:401. https://doi.org/10.3390/insects11070401.
DOI: https://doi.org/10.3390/insects11070401

Interpretive Summary: Adult house flies frequent microbe-rich sites such as urban dumpsters and animal facilities, and encounter and ingest bacteria during feeding and reproductive activities. Due to unique nutritional and reproductive needs, male and female flies demonstrate different interactions with microbe-rich substrates and therefore their dissemination potential for bacteria may differ. In this study, we determined the abundance of culturable aerobic bacteria and coliforms in male and female flies (n=107) collected from urban (restaurant dumpsters) and agricultural (dairy farm) sites. Whole fly homogenate was aerobically cultured and enumerated on nonselective media (tryptic soy agar for total culturable bacteria) and selective media (Violet-red bile agar, VRBA; for coliforms). Unique morphotypes (specific colony appearances on culture) were selected from the VRBA cultures of agricultural flies and were identified and tested for susceptibility to 14 antimicrobials. Female flies harbored more bacteria than male flies and there was a sex by site interaction with sex effects on bacterial abundance being present in flies from the urban site. Coliform abundance did not differ in male and female flies, or across site or between fly sex within sites. Both male and female flies carried antimicrobial-resistant (AMR) bacteria: 36/38 isolates (95%) were resistant to more than one antimicrobial, 33/38 were multidrug-resistant (being resistant to two or more antimicrobials), and 24/38 isolates were resistant to more than 4 antimicrobials. Our results emphasize the role that house flies play in harboring and disseminating bacteria, including AMR strains, that pose a risk to human and animal health.

Technical Abstract: Adult house flies frequent microbe-rich sites such as urban dumpsters and animal facilities, and encounter and ingest bacteria during feeding and reproductive activities. Due to unique nutritional and reproductive needs, male and female flies demonstrate different interactions with microbe-rich substrates and therefore dissemination potential. We investigated culturable aerobic bacteria and coliform abundance in male and female flies (n=107) collected from urban (restaurant dumpsters) and agricultural (dairy farm) sites. Whole-fly homogenate was aerobically cultured and enumerated on nonselective (tryptic soy agar; culturable bacteria) and selective (Violet-red bile agar, VRBA; coliforms) media. Unique morphotypes from VRBA cultures of agricultural flies were identified and tested for susceptibility to 14 antimicrobials. Female flies harbored more bacteria than males and there was a sex by site interaction with sex effects on bacterial abundance at the urban site. Coliform abundance did not differ by sex, site or sex within site. Both male and female flies carried antimicrobial-resistant (AMR) bacteria: 36/38 isolates (95%) were resistant to more than one antimicrobial, 33/38 were multidrug-resistant, and 24/38 isolates were resistant to more than 4 antimicrobials. Our results emphasize the role of house flies in harboring bacteria including AMR strains that pose a risk to human and animal health.