Multidrug-Resistant Escherichia coli, Klebsiella pneumoniae and Staphylococcus spp. in Houseflies and Blowflies from Farms and Their Environmental Settings

Background: Antimicrobial resistance is rising globally at an alarming rate. While multiple active surveillance programs have been established to monitor the antimicrobial resistance, studies on the environmental link to antimicrobial spread are lacking. Methods: A total of 493 flies were trapped from a dairy unit, a dog kennel, a poultry farm, a beef cattle unit, an urban trash facility and an urban downtown area to isolate Escherichia coli, Klebsiella pneumoniae and Staphylococcus spp. for antimicrobial susceptibility testing and molecular characterization. Results: E. coli, K. pneumoniae and coagulase-negative Staphylococcus were recovered from 43.9%, 15.5% and 66.2% of the houseflies, and 26.0%, 19.2%, 37.0% of the blowflies, respectively. In total, 35.3% of flies were found to harbor antimicrobial-resistant bacteria and 9.0% contained multidrug-resistant isolates. Three Staphylococcus aureus isolates were recovered from blowflies while three extended spectrum beta lactamase (ESBL)-carrying E. coli and one ESBL-carrying K. pneumoniae were isolated from houseflies. Whole genome sequencing identified the antimicrobial resistance genes bla(CMY-2) and bla(CTXM-1) as ESBLs. Conclusion: Taken together, our data indicate that flies can be used as indicators for environmental contamination of antimicrobial resistance. More extensive studies are warranted to explore the sentinel role of flies for antimicrobial resistance.