Antimicrobial resistance against colistin has emerged worldwide threatening the efficacy of one of the last-resort antimicrobials used for the treatment of Enterobacteriaceae. To investigate the presence of the recently identified colistin resistance genes (mcr-4， mcr-5) in China， we established PCRs to detect mcr-4 and mcr-5 on 213 anal and 1，339 nasal swabs from apparently healthy pigs (n = 1，454) in nine provinces， and 1，696 cloacal and 1，647 oropharyngeal samples from poultry (n = 1，836) at live-bird markets in 24 provinces of China. The prevalence of the mcr-4 in swine swabs (41.4%; 642/1，552) was significantly higher than in swabs from poultry (11.5%; 384/3，343). The mcr-4 gene was fou... More
Antimicrobial resistance against colistin has emerged worldwide threatening the efficacy of one of the last-resort antimicrobials used for the treatment of Enterobacteriaceae. To investigate the presence of the recently identified colistin resistance genes (mcr-4， mcr-5) in China， we established PCRs to detect mcr-4 and mcr-5 on 213 anal and 1，339 nasal swabs from apparently healthy pigs (n = 1，454) in nine provinces， and 1，696 cloacal and 1，647 oropharyngeal samples from poultry (n = 1，836) at live-bird markets in 24 provinces of China. The prevalence of the mcr-4 in swine swabs (41.4%; 642/1，552) was significantly higher than in swabs from poultry (11.5%; 384/3，343). The mcr-4 gene was found in geese (49.5%， 54/109)， chickens (17.2%， 257/1，498)， pigeons (17.2%， 17/99) and ducks (15.4%， 20/130). In a similar trend， the prevalence of the mcr-5 in swine swabs (33.1%; 514/1552) was significantly higher than in swabs from poultry (5.6%; 187/3，343). The mcr-5 was identified in geese (17.4%， 19/109)， chickens (9.9%， 148/1，498)， ducks (7.7%， 10/130) and pigeons (3%， 3/99). The mcr-4 prevalence in the nasal swabs from pigs (59.2%， 58/98) was significantly higher than that in anal swabs (29.6%， 29/98) (P<0.001). Similarly， the mcr-5 prevalence in the nasal swabs from pigs (61.2%， 60/98) was significantly higher than in anal swabs (44.9%， 44/98) (P = 0.02)， and significantly higher in oropharyngeal swabs (7.2%， 109/1，507) than in the cloacal swabs (3.7%， 56/1，507) (P<0.001). This study further confirms the presence of the mcr-4 and mcr-5 in animals and indicates these genes are prevalent and widespread in food producing animals (pig and poultry) in China. Future studies are needed to characterize the bacteria carrying the mcr-4 and mcr-5 and their locations on plasmids and/or the bacterial chromosomes， and determine co-resistances in the mcr-4 and mcr-5 positive strains.
