First identification of mcr-1/mcr-2 genes in the fecal microbiota of Canadian commercial pigs during the growing and finishing period

1Department of Pathology and Microbiology, Faculty of Veterinary Medicine, Université de Montréal, SaintHyacinthe, QC J2S 2M2, Canada; 2Department of Biochemistry, Microbiology and Bioinformatics, Faculty of Science and Engineering, Université Laval, Québec, QC G1V 4G5, Canada Colistin is considered one of the last-resort antibiotics used for the treatment of infections caused by multidrug-resistant Gram-negative bacteria (MDR-GNB) in humans. This antibiotic is classified by the World Health Organization, among the category of the Highest Priority Critically Important Antimicrobials for humanmedicine. In this regard, the global dissemination of plasmid-mediated colistin resistance, conferred by themobile colistin resistance (mcr) genes, has raised serious concern amongphysicians and scientists worldwide. On the other hand, colistin has been widely used in food animals in many countries either for disease therapy, prophylaxis or for growth promotion. Many studies reported a high prevalence of mcr genes on bacterial isolates from animals' origin compared to humans, and consequently animals, particularly pig production, were pointed out as the greatest cause of bacterial colistin resistance spread. In pigs, mcr genes were isolated mainly from colistin resistant E. coli, Salmonella and Klebsiella isolates, withmcr-1 gene being the most frequently identified gene among the eight types of mcr genes currently described. Among other Gram-negative bacteria (GNB) of pig origin, mcr genes were identified in Moraxella spp. , and in Aeromonas hydrophila, enforcing the interest to consider the mcr presence at the microbiota level. In Canada, although colistin is not approved for use in veterinarymedicine, it was sometimes used in pigs according to special precautions for the oral treatment of digestive infections caused by GNB. Nevertheless, mcr-1 gene has been identified in E. coli isolated from humans, as well as from lean ground beef in Canada. However, to the best of our knowledge,mcr genes have never been identified in animals at the farm level in Canada. Here we report the screening of fecal samples obtained from one Canadian commercial pig farm, to determine the prevalence over the growing period of mcr-1 and mcr-2 genes in the fecal microbiota of pigs. Colistin has never been used in this farm. However, tiamulin and chlortetracyclinewere used in the post-weaning period and salinomycin aswell as narasin were used during the growing phase. The present study was primarily designed to investigate the relationship between gut microbiota composition and some welfare problems in pigs (e.g., tail biting). Fecal samples have been collected between January 2017 and April 2017, from one commercial pig farm located in the province of Quebec (Canada). Pigs were sampled 5 times during the study period. In fact, fresh fecal material was collected directly from each animal’s rectum using disposable gloves, and immediately 1 g of each sample was placed in liquid nitrogen. At the laboratory, these samples were stored at −80oC until DNA extraction. In the current study, fecal samples that have Correspondence: Mohamed Rhouma Department of Pathology and Microbiology, Faculty of Veterinary Medicine, Université de Montréal, 3200 Sicotte St., Saint-Hyacinthe, QC J2S 2M2, Canada Tel +1 450 773 8521 #0096 Email mohamed.rhouma@umontreal.ca Veterinary Medicine: Research and Reports Dovepress