Health experts harbor well-grounded fears over the rise of antibiotic-resistant bacteria, and the continuing streak of newly discovered threats will do little to allay the concerns. The latest comes from scientists at Cornell University, who have discovered a previously unknown gene that can leap between organisms to facilitate resistance to an important last-resort antibiotic.

The significance of this discovery is predicated on the vital importance of the antiobotic this new gene was proven to help bacteria overcome. Colistin is regarded by the World Health Organization as a "highest priority critically important antimicrobial for human medicine," due to its role as a last-resort antibiotic used by clinicians to treat infections caused by bacteria already resistant to other, less effective medicines.

The Cornell University scientists discovered the gene in question when screening Salmonella genomes. Dubbed mcr-9, it is actually the ninth in a series of so called mcr genes, or Mobilized colistin resistance (mcr) genes, to be described by scientists since 2015. The new gene shared some characteristics with other mcr genes known to foster colistin resistance in bacteria, so the team assumed it would do the same.

Initially it did just the opposite, failing to drive colistin resistance at all. But the team knew that the mcr-9 gene was a highly mobile one, with the ability to "jump to other bacteria or organisms" where it may well wreak havoc. To explore this, Ahmed Gaballa, a microbiologist at Cornell University inserted the gene into a strain of E. Coli and switched it on, then observing how it made the E.Coli strain resistant to colistin.

"When we originally tested the salmonella isolate and found that it wasn't resistant to colistin, we were perplexed," Carroll said. "But when Ahmed cloned it into an E. coli host, he was able to find that the gene could confer resistance to colistin," says co-lead author of the study Laura Carroll.

While finding yet another superbug that can evade our most potent medicines isn't exactly ideal, the discovery is certainly a useful one, in that scientists can now screen bacteria taken from food products and in hospitals to identify mcr-9 and better manage the risks that it brings.

"If you go to a hospital and this gene is floating around, that can be trouble. The gene is moveable. It jumps," Wiedmann said. "In a hospital setting, being able to screen a patient for resistance allows doctors and nurses to isolate the patient and maintain biosecurity."

The research was published in the journal Mbio.