Abstract
Recently, a novel mobile colistin resistance gene, mcr-8, was identified in Klebsiella pneumoniae. Here, we report the identification of mcr-8 and its variant, mcr-8.4, in Raoultella ornithinolytica isolates which also belong to Enterobacteriaceae family. The mcr-8 gene was located on transferrable plasmids with difference sizes. Notably, the transferability of mcr-8-carrying plasmids was enhanced once they entered into Escherichia coli hosts and multiple β-lactamase genes could co-transfer with mcr-8. These findings expand our knowledge of mcr-8-carrying bacterial species.
Highlights
Colistin, a polypeptide antibiotic, was originally isolated from the soil bacterium Paenibacillus polymyxa subsp. colistin (Poirel et al, 2017)
PCR assays showed that two R. ornithinolytica strains, named QDRO1 and QDRO2, were positive for mcr-8, but no other mcr genes were identified in this 15 Raoultella spp strains
Conjugation assays showed that the pQDRO1 and pQDRO2 plasmids were transferable from R. ornithinolytica to recipient E. coli strains
Summary
Colistin (polymyxin E), a polypeptide antibiotic, was originally isolated from the soil bacterium Paenibacillus polymyxa subsp. colistin (Poirel et al, 2017). Colistin is effective against most Gramnegative bacteria and was considered as one of the last-resort antibiotics for the treatment of human infections caused by multidrug resistant Gram-negative bacteria, especially, carbapenem-resistant Enterobacteriaceae (CRE) (Li et al, 2006). In 2016, the first plasmid mediated colistin resistance gene mcr-1 was identified in Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa (Liu et al, 2016). The mcr-1 gene has been detected in Enterobacteriaceae isolated from food, animals, human and environment in over 50 countries across five different continents (Hembach et al, 2017; Huang et al, 2017). Plasmid-mediated colistin resistance genes mcr-2, mcr-3, mcr-4, mcr-5, mcr-6, and mcr-7 have been identified in various bacterial species from humans and animals (Partridge et al, 2018). We reported the identification of mcr-8 located on an InFII-type conjugative plasmid in Klebsiella pneumoniae isolated from chickens and pigs in China (Wang et al, 2018)
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