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 ≥1 antimicrobial, 33/38 were multidrug-resistant (≥2), and 24/38 isolates were resistant to ≥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.
Highlights
Due to the nutritional requirements of their larvae [1,2], house flies (Musca domestica L.) have life-long associations with microbe-rich substrates such as animal excrement, soiled bedding, spoiled food, and refuse [3,4,5]
Irrespective of collection date and fly sex, culturable bacterial colony-forming units (CFUs) recovered from house flies collected from urban and agricultural sites ranged from 1.49 × 102 to 1.13 × 107 CFU/fly
In the urban environment, a significant difference in mean bacterial CFU was observed between females
Summary
Due to the nutritional requirements of their larvae [1,2], house flies (Musca domestica L.) have life-long associations with microbe-rich substrates such as animal excrement, soiled bedding, spoiled food, and refuse [3,4,5]. These substrates exist in both urban and agricultural areas in places such as trash receptacles and livestock rearing/feeding operations, respectively. Wild house flies harbor both pathogenic and nonpathogenic bacteria [6,8,9], including those that are antimicrobial resistant. Because flies associate with a wide variety of microbe rich sites across the landscape, it is not surprising that they harbor different microbial communities associated with the sites with which they interact [12]
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