It has only been about 5 months since we first learned of a new resistance gene (see MCR-1: The Return Of The Plasmids) that confers resistance to a class of antibiotics called polymyxins.
Despite its nephrotoxic side effects - colistin (a polymixin) is considered an important antibiotic of last resort for some types of resistant gram negative bacteria like E. coli and Klebsiella.
Since this gene can be carried, and transferred to other bacteria via plasmids (see Study: Adaptation Of Plasmids To New Bacterial Species), the expectation is this resistance gene (like NDM-1) can spread laterally to other bacteria.
Even more worrisome, in The Lancet's Emergence of the mcr-1 colistin resistance gene in carbapenem-resistant Enterobacteriaceae, we looked at two K pneumoniae isolates that carried both the MCR-1 and NDM-5 (Carbapenem-resistance) genes, providing it near pandrug resistance.While MCR-1 has apparently been circulating under the radar for several years, we are just now beginning to understand its scope and potential impact. Today we have a brief letter describing the possible transmisison of resistant E. coli between a pet store worker and domestic animals Guangzhou, China.
I've only included some excerpts . . . follow the link to read it in its entirety.
LetterPossible Transmission of mcr-1–Harboring Escherichia coli between Companion Animals and Human
To the Editor: Plasmid-mediated, colistin-resistance mechanism gene mcr-1 was first identified in Escherichia coli isolates from food, food animals, and human patients in November 2015 (1). Reports on detection of mcr-1 in Enterobacteriaceae from humans and food animals soon followed from ≈12 countries (2–5). Here we report detection of mcr-1 in colistin-resistant E. coli isolated from companion animals and the possible transmission of mcr-1–harboring E. coli between companion animals and a person.
Results of pulsed-field gel electrophoresis were consistent with multilocus sequence typing results and showed that isolates consisted of 5 types (types I to V; Technical Appendix[PDF - 200 KB - 1 page]). Isolate EC07 was clonally related to 4 E. coli strains from dogs, according criteria described by Tenover et al. (10), suggesting possible transmission of mcr-1–harboring E. coli between dogs and the patient. Colistin resistance was successfully transferred to E. coli C600 through conjugation in all isolates, suggesting that mcr-1 was located on transferable plasmids.
These findings suggest that mcr-1–producing E. coli can colonize companion animals and be transferred between companion animals and humans. The findings also suggest that, in addition to food animals and humans, companion animals can serve as a reservoir of colistin-resistant E. coli, adding another layer of complexity to the rapidly evolving epidemiology of plasmid-mediated colistin resistance in the community.