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Published Date: 2018-03-16 10:48:26
Subject: PRO/AH/EDR> Antibiotic resistance - China: colistin, mcr-4, mcr-5, pigs, poultry
Archive Number: 20180316.5690283
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases

Date: Thu 15 Mar 2018
Source: Center for Infectious Disease Research and Policy (CIDRAP) [edited]

A research team based in China yesterday [14 Mar 2018] reported that the newly identified colistin-resistance genes MCR-4 and MCR-5 occur widely in the country's pigs and poultry, according to a study in PLoS One [1].

They used a polymerase chain reaction (PCR) test to directly detect the genes in anal and nasal swabs from 1454 apparently healthy pigs in 9 of China's provinces and cloacal and oropharyngeal samples from 1836 poultry from live-bird markets in 24 provinces.

For both of the genes, prevalence was significantly higher in swine than in poultry swabs. MCR-4 was found in 41.4 percent of pigs and 11.5 percent of poultry, and MCR-5 was present in 31.1 percent of pigs and 5.6 percent of poultry. Poultry species that harbored the gene included geese, chickens, pigeons, and ducks. In both animal types, MCR-4 and MCR-5 prevalence was higher in the nasal and oropharyngeal swabs than in anal and cloacal swabs.

Researchers found both of the genes in swabs from 2.6 percent of poultry and 18.3 percent of pigs.

The authors noted that the levels of genes detected using PCR of swabs is considerably higher than those obtained with studies on bacterial isolates and may more accurately reflect the true prevalence of the genes. "However, the data did not enable us to determine the bacterial species that carried the resistance genes, or the location of the mcr in plasmids or in the bacterial chromosomes," they wrote.

The high levels of MCR-4 and MCR-5 in pigs and poultry from a large part of China is probably linked to prolonged and widespread use of colistin -- a last-resort antibiotic -- as a growth promoter, but the 2 genes might also be prevalent in other countries, as well, the team wrote. They also said the higher levels of the genes in nasal and oropharyngeal swabs suggest that bacteria in saliva or respiratory secretions might play key roles in maintaining and transmitting colistin-resistance genes in pigs and poultry.

1. Chen L, Zhang J, Wang J, et al. Newly identified colistin resistance genes, mcr-4 and mcr-5, from upper and lower alimentary tract of pigs and poultry in China. PLoS One. 2018; 13(3): e0193957. doi: 10.1371/journal.pone.0193957; available at]

Communicated by:
ProMED-mail Rapporteur Mary Marshall

[The following is the abstract from the journal article referenced in the news report above:

"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 percent; 642/1552) was significantly higher than in swabs from poultry (11.5 percent; 384/3343). The _mcr-4_ gene was found in geese (49.5 percent, 54/109), chickens (17.2 percent, 257/1498), pigeons (17.2 percent, 17/99), and ducks (15.4 percent, 20/130). In a similar trend, the prevalence of the _mcr-5_ in swine swabs (33.1 percent; 514/1552) was significantly higher than in swabs from poultry (5.6 percent; 187/3343). The _mcr-5_ was identified in geese (17.4 percent, 19/109), chickens (9.9 percent, 148/1498), ducks (7.7 percent, 10/130) and pigeons (3 percent, 3/99). The _mcr-4_ prevalence in the nasal swabs from pigs (59.2 percent, 58/98) was significantly higher than that in anal swabs (29.6 percent, 29/98) (P less than 0.001). Similarly, the _mcr-5_ prevalence in the nasal swabs from pigs (61.2 percent, 60/98) was significantly higher than in anal swabs (44.9 percent, 44/98) (P = 0.02), and significantly higher in oropharyngeal swabs (7.2 percent, 109/1,507) than in the cloacal swabs (3.7 percent, 56/1507) (P less than 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."

The mobile colistin resistance (_mcr_) genes confer plasmid-mediated resistance to colistin, an antibiotic of last-resort used for treating Gram-negative bacillary infections resistant to most other antibiotics. Location on a plasmid allows spread of colistin resistance within and between different species of bacteria through horizontal gene transfer. There are now 5 _mcr_ genes (_mcr-1_, _mcr-2_, _mcr-3_, _mcr-4_, and _mcr-5_), and variants of those genes, each with different DNA sequences. _mcr-1_ was first described in China in 2015 and then elsewhere in the world in various bacterial isolates (such as _Escherichia coli_, _Salmonella enterica_, _Klebsiella pneumoniae_, _Enterobacter aerogenes_, and _Enterobacter cloacae_) isolated from humans, multiple other animal species, and the environment. As of 2017, _mcr-1 has been detected in more than 30 countries on 5 continents (

A map of the US that displays where the _mcr-1_ gene has been reported in human and food animal sources as of 1 Mar 2018 can be found at The map is updated monthly. - Mod.ML

HealthMap/ProMED-mail map

See Also

Antibiotic resistance (05): China, colistin, mcr-1, hospital outbreak 20170527.5066686
Antibiotic resistance (01): China, colistin, MCR-1 clin. Enterobacteriaceae isolates 20170129.47998712016
Antibiotic resistance - France: non-MCR-1, colistin/carbapenem, 2014 20160916.4492825
Antibiotic resistance - USA (05): colistin, MCR-1, E. coli, new case, contacts 20160911.4479863
Antibiotic resistance - USA (04): (NJ) colistin/carbapenem, MCR-1, E. coli, human 20160902.4459453
Antibiotic resistance - Europe, Canada: colistin, MCR-1, E. coli, bovine, human 20160808.4400601
Antibiotic resistance - Germany: colistin, MCR-1, E. coli, poultry, 2010 - 2015 20160728.4374873
Antibiotic resistance - Belgium: colistin, MCR-2, plasmid, E. coli, pigs, calves 20160709.4335297
Antibiotic resistance - Portugal: colistin, MCR-1, Salmonella, Cu tolerance 20160703.4323241
Antibiotic resistance - USA (03): (NY) colistin, MCR-1, E. coli, human 20160630.4317770
Antibiotic resistance - multicountry: colistin, MCR-1, E. coli, gull 20160630.4313655
Antibiotic resistance - USA (02): colistin, MCR-1, E. coli, pig 20160616.4290293
Antibiotic resistance - USA: colistin, MCR-1, E. coli, human, pig 20160528.4251552
Antibiotic resistance - Italy: colistin, MCR-1, E. coli, turkeys, 2014 20160113.3933461
Antibiotic resistance - Canada: colistin, MCR-1, E. coli, grd. beef, human, 2010 20160106.3915891
Antibiotic resistance: colistin, MCR-1, multi-continent spread, human, animal 20151219.3875812
Antibiotic resistance - Netherlands: colistin, MCR-1, salmonella, poultry meat 20151217.3870429
Antibiotic resistance - Denmark: colistin, MCR-1, salmonella, human, chicken, RFI 20151206.3844715
Antibiotic resistance - UAE: panresist. K. pneum, mobile chrom. colistin-resist. 20151126.3820586
Antibiotic resistance - China: colistin, plasmid-encoded, humans, animals 20151122.3810204

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