Dissemination of the mcr 1 colistin resistance gene.
292 www.thelancet.com/infection Vol 16 March 2016 These findings confirm our initial concern that mcr 1 could have already disseminated worldwide. Sequencing data show that mcr 1 is carried by plasmids of various replicon types, including IncI2, IncHI1 (GenBank accession number JWKJ01000115) IncP, IncX4, and IncHI2 (GenBank accession number LFCC01000022) In the strain SHP45 from which mcr 1 was fi rst discovered, S1 PFGE and hybridisation showed that the gene was on two plasmids: the 64 kb pHNSHP45 (IncI2) in the original report, and also a larger plasmid of roughly 244 kb, which was not transferred by conjugation in our previous experimental conditions. To further investigate this second mcr 1carrying plasmid, we did conjugation experiments with screening plates supplemented with various antibiotics that the original strain SHP45 showed resistance to (gentamicin, fl orfenicol, olaquindox, co trimoxazole, neo mycin, and ampicilin) Trans con jugants were successfully obtained from all screening plates with a conjugation frequency of roughly 10 per recipient. S1 PFGE confirmed that the transconjugants only carried the 244 kb plasmid. In addition to colistin, the transconjugant also showed elevated minimum inhibitory con centrations to ampicillin, cefo taxime, apramycin, neomycin, gentamicin, florfenicol, olaquindox, co trimoxazole, fosfomycin, and ciprofloxacin. The plasmid, named pHNSHP45 2, was fully sequenced by PacBio RS II (Pacifi c Biosciences, Manlo Park, CA, USA) S e q u e n c i n g r e v e a l e d t h a t pHNSHP45 2 is 251 493 base pairs and belongs to the IncHI2 plasmid. The plasmid backbone of pHNSHP45 2 is almost identical to that of pHXY0908 (GenBank accession number KM877269) from salmonella recovered from a chicken in Guangdong province of China, and pHK0653 (GenBank accession number KT334335) from salmonella of human origin in Hong Kong (appendix) but the variable regions were distinct. The all strains had a colistin minimum inhibitory concentration between 4 and 16 mg/mL, and were resistant to cephalosporins due to coexistence of the CTX M 15 b lactamase gene; resistance to levofl oxacin, amikacin, and meropenem was also common. In summary, our data suggest that human gut fl ora, especially the E coli subpopulation, have a role in facilitating dissemination of the mcr 1 element by absorbing genetic materials from external sources. The rate of mcr 1 transmission would certainly accelerate as a result of increase in the rate of faecal carriage of this element and clinical use of colistin.
The Lancet. Infectious diseases