“…It should be noted that before 2005 there were no reports that identified the mcr -harboring isolates and most of the isolates currently reported to be mcr positive are historical isolates, dating back to as early as 1980. Similarly, global trade and travel either to countries with high or unknown prevalence (Canada [20], U.S. [21] and Japan [22]), importation of food from infected countries (Japan [23] and Tunisia [24]), and over-prescription of colistin in human medicine to treat highly resistant clinical pathogens (i.e., Argentina [25]) are also the suggested causes. To date, several other mcr gene variants have been identified, including mcr-2, -3, -4, -5, -6, -7, and -8 , which share 81%, 32%, 34%, 36%, 83%, 35%, and 31% amino acid sequence identity, respectively, with mcr-1 [26].…”