Last Resort Antibiotic Resistance Found

Cornell University research discovered the gene which belongs to a class of plasmid borne genes that confer resistance to colistin. 8 known mcr homologues have been previously described, this gene was found in Salmonella enterica serotype Typhimurium genome while screening Salmonella genomes for antimicrobial resistance by Laura Carroll, as published in mBio.

“This last-resort antibiotic has been designated a highest-priority antibiotic by the United Nations’ World Health Organization, and the mcr-9 gene causes bacteria to resist it. In treatments, if colistin does not work, it literally could mean death for patients.” explains Martin Wiedmann PhD.

Until plasmid mediated colistin resistance gene mcr-1 was described bacterial resistance to colistin was thought to be acquired via chromosomal point mutations. Since then 7 additional mcr homologues have been identified in Enterobacteriaceae; mcr-9 is the latest addition in this new series of mobilized colistin resistance genes. Amino acid sequencing of the newly identified gene closely resembles mcr-3, and expression conferred resistance to colistin in E.coli; pairwise comparisons of predicted protein structures associated with all 9 mcr homogues reveal mcr-9,3,4,and 7 all share a high degree of similarity at the structural level.

“Plasmid-borne mcr genes that confer resistance to colistin pose a threat to public health at an international scale, as they can be transmitted via horizontal gene transfer and have the potential to spread globally. If you go to a hospital and this gene is floating around, that can be trouble. The gene is moveable. It jumps, in a hospital setting, being able to screen a patient for resistance allows doctors and nurses to isolate the patient and maintain biosecurity.” says Wiedmann.

Colistin is a last resort antibiotic used to treat severe infections caused by MDR and drug resistant bacteria; establishment of a complete reference of mcr gene that can be used to screen for plasmid mediated colistin resistance is important to developing effective control strategies.