Antimicrobial drug resistance has been increasing over the past two decades and now humanity has come to the edge of a “post-antibiotic era”. Inappropriate and extensive use of antibiotics in human and veterinary medicine as well as in agriculture causes antibiotic resistance in pathogenic bacteria. Colistin is an antibiotic used in treating infections caused by Gram-negative bacteria. Also, it is a last-resort antibiotic because of its side effects in human treatments. Although the use of antibiotics as growth promoters in animal husbandry has been banned in many countries, colistin was continued to be used in veterinary medicine for decades not only for treatment but also for prevention of diseases and metaphylaxis. Since the discovery of colistin resistance transmission through plasmids, ten plasmid-mediated mcr genes have been described already from different pathogenic bacteria originating from various sources including food.