Chengming Wang, Kezong Qi, Afrah Kamal Yassin, Jiawei Wang, Russell Cattley, Jing Li, Patrick Butaye, Jilei Zhang, Jiansen Gong, Patrick Kelly, Li Chen
Flies have the capacity to transfer pathogens between different environments, acting as one of the most important vectors of human diseases worldwide. In this study, we trapped flies on a university campus and tested them for mobile resistance genes against colistin, a last-resort antibiotic in human medicine for treating clinical infections caused by multidrug-resistant Gram-negative bacteria. Quantitative PCRs we developed showed that 34.1% of Musca domestica (86/252) and 51.1% of Protophormia terraenovae (23/45) were positive for the mcr-1, 1.2% of M. domestica (3/252) and 2.2% of P. terraenovae (2.2%, 1/45) were positive for the mcr-2, and 5.2% of M. domestica (13/252) and 44.4% of P. terraenovae (20/45) were positive for the mcr-3 Overall, 4.8% (9/189) of the bacteria isolated from the flies were positive for the mcr-1 (Escherichia coli: 8.3%, 4/48; Enterobacter cloacae: 12.5%, 1/8; Providencia alcalifaciens: 11.8%, 2/17; Providencia stuartii, 4.9%, 2/41) while none were positive for the mcr-2 and mcr-3 Four mcr-1 positive isolates (two P. stuartii and two P. alcalifaciens) from blow flies trapped near the dumpster had a MIC above 4 mg colistin/mL. This study reports mcr-1 carriage in Providencia spp. and detection of mcr-2 and mcr-3 after their initial identification in Belgium and China, respectively. This study suggests flies might contribute significantly to the dissemination of bacteria carrying these genes into a large variety of ecological niches. Further studies are warranted to explore the roles that flies might play in the spread of colistin resistance genes.Importance Antimicrobial resistance is recognized as one of the most serious global threats to human health. An option for treatment of the Gram-negative ESKAPE bacteria with multiple drug resistance was the reintroduction of the older antibiotic colistin. However, a mobile colistin resistance genes (mcr-1) has recently been found to occur widely; very recently, two other colistin resistance genes (mcr-2, and mcr-3) have been identified in Belgium and China, respectively. In this study, we report the presence of colistin resistance genes in flies. This is also the first report of the carriage of colistin resistance in the genus Providencia, and the first detection of mcr-2 and mcr-3 after their initial identification. This study will stimulate more in-depth studies to fully elucidate the transmission mechanisms of the colistin resistance genes and their interaction.