Abstract
The objective of this review is to collect and present the results of relevant studies on an international level, on the subject of colistin resistance due to mcr genes prevalence in livestock animals. After a literature search, and using PRISMA guidelines principles, a total of 40 swine, 16 bovine and 31 poultry studies were collected concerning mcr-1 gene; five swine, three bovine and three poultry studies referred to mcr-2 gene; eight swine, one bovine, two poultry studies were about mcr-3 gene; six swine, one bovine and one poultry manuscript studied mcr-4 gene; five swine manuscripts studied mcr-5 gene; one swine manuscript was about mcr-6, mcr-7, mcr-8, mcr-9 genes and one poultry study about mcr-10 gene was found. Information about colistin resistance in bacteria derived from animals and animal product foods is still considered limited and that should be continually enhanced; most of the information about clinical isolates are relative to enteropathogens Escherichia coli and Salmonella spp. This review demonstrates the widespread dispersion of mcr genes to livestock animals, indicating the need to further increase measures to control this important threat for public health issue.
Highlights
Colistin as an antimicrobial agent belongs to the polymyxin antibiotic class and it is produced by Paenibacillus polymyxa, which is a Gram-positive bacterium
Swine-pathogenic E. coli strains were isolated from farm animals, but not food products and mcr-1 gene was detected in 90 (13%) strains, while the MICs for these mcr-1–positive strains ranged from 8 to 128 mg/mL. These results suggest that a great proportion of swine-pathogenic E. coli in Japan is resistant to colistin, that mcr-1 has already a wide prevalence and that there is a similarity between the level of colistin resistance mediated by mcr-1 and the level of resistance mediated by mcr-1–independent mechanisms [95]
Polymyxins are becoming a last resort antimicrobial in human medicine and for that reason National Competent Authorities and the farming industry are taking measures to diminish the use of colistin in food-producing animals and especially in poultry and swine, as E.M.A. demanding (EMA/CVMP/CHMP, 2016)
Summary
Colistin as an antimicrobial agent belongs to the polymyxin antibiotic class and it is produced by Paenibacillus polymyxa, which is a Gram-positive bacterium. This antibiotic class consists of five polymyxins, A, B, C, D, and E from which polymyxin E (colistin) and polymyxin B are used clinically [1,2,3]. Polymyxins antibacterial spectrum is narrow, mainly against common Gram-negative bacteria. They are active against most of the bacteria of Enterobacteriaceae family, including Escherichia coli, Enterobacter spp., Klebsiella spp., Citrobacter spp., Salmonella spp., and Shigella spp. Due to observation of a post antibiotic effect against K. pneumoniae, P. aeruginosa, and A. baumannii [9,10,11], polymyxins are used as a last-resort treatment option against them [12,13,14]
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