Genetic antibiotic resistance mechanism continues to spread

A recently discovered genetic mechanism allowing bacteria to develop and transfer resistance to colistin — one of the last-resort antibiotics — has been present in countries across the world for more than a decade, according to presenters at ECCMID 2016 — the annual meeting of the European Society of Clinical Microbiology and Infectious Disease.

At a session dedicated to colistin resistance, researchers presented findings on the prevalence of the mcr-1 gene, a transferable genetic mechanism of antimicrobial resistance to colistin. The mechanism, first discovered in an E. coli strain from a pig in China in November 2015, has over the past months been identified in bacterial samples across the world.

The gene is particularly significant as it can be carried by plasmids — small DNA molecules — which can be transferred between single-celled organisms, such as bacteria, through horizontal gene transfer. These genes can then be transferred sideways to other strains or species — not just vertically down to the offspring by replication. Horizontal gene transfer is the primary reason for antibiotic resistance.

“The mcr-1 gene has recently taken centre stage in the ongoing fight against antibiotic resistance as we are concerned that resistance this colistin resistance mechanism may be transferred between different bacterial species,” said ECCMID Programme Director Professor Winfried Kern. “The antibiotic colistin is in some cases already the only treatment option clinicians have left.”

The increased prevalence of plasmid-mediated resistance is causing major concern among infectious disease specialists, because it threatens to reduce options to treat infections and is creating new resistant bacterial strains. But while the ECCMID session saw evidence presented on the prevalence of the gene in bacteria (including Enterobacteriaceae such as E. coli, Salmonella or Klebsiella), it also looked at treatment and management options as well as new diagnostic methods and assays to help identify the gene.

“Understanding the spread of mcr-1 and the underlying resistance mechanism will allow us to develop more effective diagnostics, treatments and stewardship programs to better manage infections caused by multiresistant pathogens,” said Professor Kern.