A Novel Variant Carried by an IncI2-Type Plasmid Identified From a Multidrug Resistant Enterotoxigenic .

In this study, we discovered a novel mobilized colistin resistance () gene variant, named , which was identified in a colistin-resistant enterotoxigenic (ETEC) strain from a clinical diarrhea case. The gene differs from at position 1036 due to a single nucleotide polymorphism (G→A), which results in an aspartic acid residue being replaced by an asparagine residue (Asp346→Asn) in the MCR-1 protein sequence. Antimicrobial susceptibility testing showed that the -harboring ETEC strain is resistant to colistin at a minimum inhibitory concentration of 4 μg/ml. Plasmid profiling and conjugation experiments also suggest that the variant can be successfully transferred into the strain J53, indicating that the gene is located on a transferable plasmid. Bioinformatics analysis of data obtained from genome sequencing indicates that the gene is located on a 64,005 bp plasmid which has been named pEC26. This plasmid was found to have high similarity to the -bearing IncI2-type plasmids pWF-5-19C (99% identity and 99% coverage) and pmcr1-IncI2 (99% identity and 98% coverage). The harboring ETEC also shows multidrug resistance to nine classes of antibiotics, and contains several virulence and antimicrobial-resistance genes suggested by the genome sequence analysis. Our report is the first to identify a new variant in an ETEC isolated from a human fecal sample, raising concerns about the existence of more such variants in human intestinal flora. Therefore, we believe that an undertaking to identify new variants in the bacterial communities of human intestines is of utmost importance, and that measures need to be taken to control the spread of and its variants in human intestinal microflora.