LETTER
The plasmid-mediated colistin resistance gene mcr-1 was first reported in China in 2013 and has since been identified in both humans and livestock from many other countries (1–4). Colistin has been approved for animal use for prevention and treatment of disease in Korea. We investigated the prevalence of this gene in food animals and animal products in Korea.
In total, 10,576 Escherichia coli isolates were obtained from fecal and carcass samples from healthy animals at slaughterhouses and from tissue lesions or fecal samples of diseased animals at diagnostic laboratories from 2005 to 2015 in the Korean Veterinary Antimicrobial Resistance Monitoring System.
Testing for susceptibility to 15 antimicrobials in the 10,576 E. coli isolates and 8 transconjugants was performed by the broth microdilution method using the KRNV4F Sensititre panel (Trek Diagnostic Systems) according to the manufacturer's instructions (5). The results for colistin were interpreted according to the European Committee on Antimicrobial Susceptibility Testing breakpoint (>2 μg/ml). mcr-1 gene carriage was determined by PCR and DNA sequencing for colistin-resistant E. coli isolates (1).
Of the 10,576 E. coli isolates tested, 154 (1.46%) exhibited colistin resistance. The colistin-resistant isolates were obtained from cattle and cattle carcasses (1.28%, 45/3,523), pigs and pig carcasses (1.71%, 66/3,865), and chickens and chicken carcasses (1.35%, 43/3,188) (Table 1). Interestingly, isolates from diseased animals showed much higher resistance than isolates from healthy animals or carcasses at the slaughterhouse (P < 0.01). The annual consumption of colistin by food animals in Korea, ranging from 6 to 16 tons during 2005 to 2015, might contribute to the occurrence of colistin resistance.
TABLE 1.
Colistin resistance and carriage of the mcr-1 gene in Escherichia coli isolates obtained from animals and animal carcasses between 2005 and 2015
| Yr | % resistance (no. of resistant isolates/no. of tested isolates)a |
% of isolates with colistin resistance (no. of resistant isolates/no. of tested isolates) | % of isolates in which mcr-1 gene was detected (no. of positive isolates/no. of tested isolates) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Healthy cattle | Diseased cattle | Cattle carcasses | Healthy pigs | Diseased pigs | Pig carcasses | Healthy chickens | Diseased chickens | Chicken carcasses | |||
| 2005 | 0.8 (1/118) | NT | 0 (0/78) | 0 (0/176) | NT | 0 (0/89) | 0 (0/113) | NT | 0 (0/119) | 0.14 (1/693) | 0 (0/639) |
| 2006 | 0 (0/120) | NT | 0 (0/82) | 2.6 (5/190) | NT | 0 (0/85) | 0 (0/138) | NT | 0 (0/129) | 0.67 (5/744) | 0 (0/744) |
| 2007 | 9.9 (12/121) | NT | 0 (0/57) | 7.1 (17/239) | NT | 0 (0/62) | 0 (0/169) | NT | 0 (0/96) | 3.90 (29/744) | 0 (0/744) |
| 2008 | 12.8 (16/125) | NT | 0 (0/51) | 5.2 (6/116) | NT | 0 (0/61) | 0.9 (1/106) | NT | 0 (0/100) | 4.11 (23/559) | 0 (0/559) |
| 2009 | 2.7 (5/184) | NT | 0 (0/51) | 3.8 (7/185) | NT | 0 (0/48) | 2.1 (2/97) | NT | 0 (0/76) | 2.18 (14/641) | 0 (0/641) |
| 2010 | 0 (0/231) | 0 (0/21) | 0 (0/136) | 0.9 (2/221) | 1.8 (1/56) | 0.8 (1/124) | 5.2 (8/155) | 4.0 (2/50) | 0 (0/107) | 1.27 (14/1,101) | 0 (0/1,101) |
| 2011 | 1.2 (4/347) | 0 (0/14) | 1.1 (2/190) | 0.9 (2/231) | 5.6 (2/36) | 0.7 (1/153) | 2.1 (3/141) | 11.6 (5/43) | 3.3 (4/121) | 1.80 (23/1,276) | 0 (0/1,276) |
| 2012 | 0 (0/282) | 0 (0/28) | 0 (0/111) | 0.7 (2/277) | 0 (0/39) | 0.7 (1/134) | 0 (0/200) | 0 (0/8) | 0 (0/163) | 0.24 (3/1,242) | 0 (0/1,242) |
| 2013 | 1.0 (2/209) | 0 (0/5) | 0 (0/146) | 0 (0/199) | 10.7 (3/28) | 1.4 (2/141) | 1.1 (2/187) | 0 (0/33) | 0.8 (1/130) | 0.93 (10/1,078) | 0.09 (1/1,078) |
| 2014 | 0.3 (1/299) | 12.5 (1/8) | 0 (0/159) | 0.3 (1/294) | 15.8 (6/38) | 0 (0/160) | 1.6 (3/192) | 10.3 (4/39) | 3.6 (5/140) | 1.58 (21/1,329) | 0.45 (6/1,329) |
| 2015 | 0 (0/206) | 5.3 (1/19) | 0 (0/125) | 0 (0/218) | 4.5 (7/154) | 0 (0/111) | 1.1 (2/189) | 0 (0/20) | 0.8 (1/127) | 0.94 (11/1,169) | 0.34 (4/1,169) |
| Total | 1.8 (41/2,242) | 2.1 (2/95) | 1.2 (2/1,186) | 1.8 (42/2,346) | 5.4 (19/351) | 0.4 (5/1,168) | 1.2 (21/1,687) | 5.7 (11/193) | 0.8 (11/1,308) | 1.46 (154/10,576) | 0.10 (11/10,576) |
NT, not tested.
Notably, the mcr-1 gene was detected in 0.10% (11/10,576) of isolates that originated from 10 different farms in four provinces; for these isolates, colistin MICs ranged from 8 to 16 μg/ml. Sequencing revealed that the mcr-1 amplicons were 100% identical to that reported by Liu et al. (1). Of note, mcr-1 was found mainly in isolates collected from poultry; five each were from healthy chicken fecal samples and chicken carcasses, and one was from a diseased pig. mcr-1 was not detected in E. coli isolates before 2013, but its prevalence has risen since 2013 (0.09% [1/1,078] in 2013, 0.45% [6/1,329] in 2014, and 0.34% [4/1,169] in 2015) (P < 0.01). This result was different from those of other studies, in which generally mcr-1 carriage corresponded to increased colistin resistance (4). Further studies are necessary to explain the higher prevalence of mcr-1-carrying E. coli isolates in healthy chickens and carcasses than in diseased chickens and carcasses even though the resistance rate is low.
All 11 mcr-1-carrying isolates displayed multiple-drug resistance (≥3 antimicrobial subclasses), which was successfully transferred to an E. coli J53 recipient strain by filter mating but not to 3 other isolates; no other resistance was cotransferred. All the mcr-1-carrying isolates were from different farms and showed different pulsed-field gel electrophoresis (PFGE) patterns and sequence types (STs), with the exception of two ST162 isolates that carried the blaCTX-M-1 gene (Table 2). Importantly, multilocus sequence typing and XbaI PFGE results (see Fig. S1 in the supplemental material) indicated that the rise of mcr-1-carrying isolates may be driven by plasmid-mediated horizontal gene transfer rather than by the spread of a specific clone.
TABLE 2.
Characteristics of the mcr-1-positive Escherichia coli isolates from animals and animal carcasses
| Isolate | Sample | Province | Yr | MIC (μg/ml) ofa: |
Resistance transferred | ST | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GEN | NEO | STR | AMP | AmC | CEF | FOX | XNL | CIP | SXT | CHL | FFC | COL | NAL | TET | ||||||
| S03-109 | Chicken carcass | Chungnam | 2013 | ≤1 | ≤2 | >128 | >64 | 8 | 16 | 8 | ≤0.5 | >16 | 0.25 | 8 | 4 | 8 | >128 | 4 | Yes | 410 |
| A03-007 | Healthy chicken | Chungbuk | 2014 | ≤1 | ≤2 | 8 | >64 | 8 | 16 | 4 | ≤0.5 | 8 | >4 | 4 | 4 | 8 | >128 | ≤2 | Yes | 156 |
| S03-009 | Chicken carcass | Chungnam | 2014 | ≤1 | ≤2 | 128 | >64 | 8 | 8 | 2 | ≤0.5 | 8 | ≤0.12 | 64 | >64 | 8 | >128 | 32 | Yes | 10 |
| A03-008 | Healthy chicken | Jeonnam | 2014 | ≤1 | ≤2 | 8 | >64 | 8 | 16 | 4 | ≤0.5 | 16 | 0.25 | >64 | 4 | 8 | >128 | ≤2 | No | 101 |
| A03-017 | Healthy chicken | Chungbuk | 2014 | ≤1 | ≤2 | >128 | >64 | 8 | 16 | 4 | ≤0.5 | 8 | >4 | >64 | >64 | 8 | >128 | >128 | Yes | 226 |
| S03-006 | Chicken carcass | Chungbuk | 2014 | ≤1 | ≤2 | >128 | >64 | 8 | >64 | 2 | 8 | 8 | 0.25 | 64 | 64 | 8 | >128 | 64 | Yes | 162 |
| S03-031 | Chicken carcass | Jeonnam | 2014 | ≤1 | ≤2 | >128 | >64 | 8 | 8 | 4 | ≤0.5 | 0.25 | 0.5 | >64 | >64 | 8 | 128 | 128 | No | 88 |
| S03-026 | Chicken carcass | Gyeonggi | 2015 | 64 | ≤2 | 128 | >64 | 8 | 16 | 4 | ≤0.5 | 16 | >4 | 8 | 4 | 8 | >128 | 128 | Yes | 2732 |
| A03-003 | Healthy chicken | Jeonnam | 2015 | ≤1 | ≤2 | 8 | >64 | 4 | 8 | 4 | ≤0.5 | 1 | ≤0.12 | >64 | >64 | 8 | 128 | 128 | No | 1141 |
| A03-010 | Healthy chicken | Jeonnam | 2015 | ≤1 | ≤2 | >128 | >64 | 4 | >64 | 2 | >8 | 8 | 0.25 | >64 | 64 | 8 | >128 | 64 | Yes | 162 |
| R02-111 | Diseased pig | Chungbuk | 2015 | 16 | ≤2 | >128 | >64 | 8 | 8 | 4 | ≤0.5 | ≤0.12 | >4 | 64 | 64 | 16 | ≤2 | 64 | Yes | 1 |
GEN, gentamicin; NEO, neomycin; STR, streptomycin; AMP, ampicillin; AmC, amoxicillin-clavulanic acid; CEF, cephalothin; FOX, cefoxitin; XNL, ceftiofur; CIP, ciprofloxacin; SXT, trimethoprim-sulfamethoxazole; CHL, chloramphenicol; FFC, florfenicol; COL, colistin; NAL, nalidixic acid; TET, tetracycline; ST, sequence type.
This is the first report of the mcr-1 gene in South Korea. Although the rate of colistin resistance in healthy animals and animal products remains low, restriction of the use of colistin is essential to prevent the transmission of mcr-1 to other bacteria in the same or different animals, to the food chain, and to the human community.
Supplementary Material
ACNKOWLEDGMENT
This study was supported by a grant from the Animal and Plant Quarantine Agency, Ministry of Agriculture, Food, and Rural Affairs, Republic of Korea (N-1543081-2015-24-01).
Footnotes
Supplemental material for this article may be found at http://dx.doi.org/10.1128/AAC.01472-16.
REFERENCES
- 1.Liu YY, Wang Y, Walsh TR, Yi LX, Zhang R, Spencer J, Doi Y, Tian G, Dong B, Huang X, Yu LF, Gu D, Ren H, Chen X, Lv L, He D, Zhou H, Liang Z, Liu JH, Shen J. 2016. Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study. Lancet Infect Dis 16:161–168. doi: 10.1016/S1473-3099(15)00424-7. [DOI] [PubMed] [Google Scholar]
- 2.McGann P, Snesrud E, Maybank R, Corey B, Ong AC, Clifford R, Hinkle M, Whitman T, Lesho E, Schaecher KE. 2016. Escherichia coli harboring mcr-1 and blaCTX-M on a novel IncF plasmid: first report of mcr-1 in the United States. Antimicrob Agents Chemother 60:4420–4421. doi: 10.1128/AAC.01103-16. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Suzuki S, Ohnishi M, Kawanishi M, Akiba M, Kuroda M. 2016. Investigation of a plasmid genome database for colistin-resistance gene mcr-1. Lancet Infect Dis 16:284–285. doi: 10.1016/S1473-3099(16)00008-6. [DOI] [PubMed] [Google Scholar]
- 4.Shen Z, Wang Y, Shen Y, Shen J, Wu C. 2016. Early emergence of mcr-1 in Escherichia coli from food-producing animals. Lancet Infect Dis 16:293. doi: 10.1016/S1473-3099(16)00061-X. [DOI] [PubMed] [Google Scholar]
- 5.Tamang MD, Gurung M, Nam HM, Moon DC, Kim SR, Jang GC, Jung DY, Jung SC, Park YH, Lim SK. 2015. Prevalence and characterization of Salmonella in pigs from conventional and organic farms and first report of S. serovar 1,4,[5],12:i:– from Korea. Vet Microbiol 178:119–124. doi: 10.1016/j.vetmic.2015.05.005. [DOI] [PubMed] [Google Scholar]
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