Identification of mobile colistin resistance genes (mcr-1.1, mcr-5, mcr-8.1) in Enterobacteriaceae and Alcaligenes faecalis of human and animal origins, Nigeria

Emmanuel O Ngbede, Anil Poudel, Anwar Kalalah, Yi Yang, Folasade Adekanmbi, Alex A Adikwu, Andrew M Adamu, Levi M Mamfe, Salem T Terwase, Nicodemus M Useh, Jacob K P Kwaga, Mohammed I Adah, Patrick Kelly, Patrick Butaye, Chengming Wang
International Journal of Antimicrobial Agents 2020 July 25, : 106108
Colistin is a last resort drug used to treat infections caused by multidrug resistant Gram-negative bacteria that have developed resistance to carbapenem. The emergence and rapid dissemination of the nine plasmid-mediated mobile colistin resistance genes (mcr-1 to mcr-9) has led to fear of pan-drug resistant infections occurring worldwide. To date, there is only limited information on colistin resistance in African countries where the drug is widely used in agriculture. In this study from Nigeria, 583 non-duplicate bacterial strains were isolated from 1,119 samples collected from humans, camels, cattle, dogs, pigs and poultry by the use of colistin-supplemented MacConkey agar, and 17.0% of the isolates (99/583) were colistin resistant. PCRs (mcr-1 to mcr-9) and whole genome sequencing (WGS) identified mcr in 21.2% of the colistin-resistant isolates: mcr-1.1 (n=13), mcr-8.1 (n=5), both mcr-1.1 and mcr-8.1 (n=2), and mcr-1.1 and mcr-5 (n=1). Nine of the 21 mcr-positive strains were isolated from human samples, with eight being K. pneumoniae, and six of these human K. pneumoniae had a high colistin MIC of >64 µg/ml. In contrast, nine of the 12 mcr-positive animal isolates were E. coli of which only two had a colistin MIC of >64 µg/ml. Our study is the first to report mcr-1 in Alcaligenes faecalis, and emergence of mcr-5 and mcr-8 in Nigeria. WGS determined that mcr-1 was localized on IncX4 plasmid, and 95.2% of mcr-1 harboring isolates (20/21) transferred colistin resistance successfully in conjugation assay. Our findings highlight the global spread of colistin resistance, and emphasize the urgent need for coordinated global action to combat resistant bacteria.

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