MCR: modern colistin resistance.

Recently, plasmid-mediated and, therefore, transferable bacterial polymyxin resistance was discovered in strains from both humans and animals. Such a trait may widely spread geographically, while simultaneously crossing microbial species barriers. This may ultimately render the "last resort" polymyxin antibiotics therapeutically useless. Colistin is currently used to treat infections caused by Gram-negative carbapenemase producers and colistin resistance may lead to practical pan-antibiotic resistance. We here analyzed the medical and diagnostic consequences of (emerging) colistin resistance and propose pathways toward adequate diagnostics for timely detection of both asymptomatic carriage and infection. Culture-based testing using chromogenic and selective media for screening clinical (and veterinary) specimens may constitute key tools for that purpose. Relevant molecular tests are also discussed.