D3026: (1st Place) Assessment of AMR bacteria carried by house flies collected at confined cattle operations in Kansas

House flies are persistent pests that thrive in confined cattle operations due to abundant microbe-rich larval developmental substrates like manure. House flies acquire microbes from manure and animals and serve as reservoirs and vectors of pathogenic and antimicrobial-resistant (AMR) bacteria. Identifying factors influencing the abundance and prevalence of bacteria and AMR carried by house flies could help improve AMR mitigation. Adult house flies and abiotic factors, including manure management and climate variables, were collected from six KS dairy and beef operations from August through October of 2019. Fly homogenate was cultured on non-selective media to enumerate overall bacteria and on violet-red bile agar to select and enumerate coliforms. Distinct coliform morphotypes were subcultured and initially screened for tetracycline resistance on selective media then tested for multi-drug resistance (MDR) to tetracycline, florfenicol, enrofloxacin, ceftiofur, and/or ampicillin using the Kirby-Bauer method. Genus-level identification of MDR coliforms was performed via 16S rRNA gene sequencing. Fly sex, average temperature, and rainfall significantly influenced the abundance of overall bacteria and coliforms carried by house flies regardless of farm type. House flies from beef operations carried a greater diversity of MDR coliform phenotypes than flies from dairies. The most common MDR taxa were Escherichia/Shigella spp. or Klebsiella spp. which were dual- or triple-resistant to tetracycline, florfenicol, and/or ampicillin. Our results implicate house flies as significant sources and disseminators of AMR bacteria and give insight into climate variables that might enhance risks to human or animal health associated with bacterial carriage by house flies.