Colistin is a cationic cyclic peptide that disrupts bacterial cell membranes of Gram-negative bacteria. It is one of the few remaining antibiotics of last resort for use against infections with multidrug-resistant bacteria. Hence, the recent global detection of transferable mobile colistin resistance gene families in a wide range of multi-resistant Gram-negative bacteria isolated from all kinds of environments—clinical, veterinary, food-products and aquaculture—has sounded alarm bells.