Superbug Discovery Overturns Long-Held Public Health Beliefs

A new study published in Nature Communications reveals a hidden source of antibiotic resistance, providing an early warning sign for researchers and public health officials. 

The novel gene found in contaminated freshwater NSW sediment, by researchers at Macquarie University and The University of Sydney, provides bacteria with resistance to polymyxin - a critical last line antibiotic, used when others stop working. 

The mcr-12 gene is the first of its kind to be discovered outside a clinical, food or livestock setting. It's also the first to be initially found outside a non-Gammaproteobacterial host (such as E. coli) and the first in the Southern Hemisphere. Scientists discovered mcrgenes only a decade ago, and since then believed they were only found in bacteria from hospitals, patients or livestock. 

Polymyxin resistance genes are typically associated with settings where there has been direct antibiotic exposure, so this discovery challenges our previous assumptions."

Brodie Gillieatt, Lead Researcher, Macquarie University 

Concerningly, the gene still worked when it moved from its original host to several different pathogenic bacteria, - a problem if the gene spread to a clinical setting. 

Professor of Microbiology at Macquarie University, Amy K. Cain says the discovery is timely. "The gene has not yet spread to major human pathogens. Detecting it now, gives researchers and public health officials a chance to monitor its spread before it becomes a widespread clinical problem." 

The gene was also found to be associated with heavy metal resistance genes in freshwater, contaminated by heavy metals - raising the possibility that metal pollution could help maintain antibiotic resistance genes. 

"It highlights the role of environmental pollution in antibiotic resistance meaning environmental management may also play a role in slowing the spread," says Dr Gillieatt. "These types of resistance genes are likely circulating in wider environmental reservoirs, and we simply have not invested in their detection until now. We need broader surveillance." 

Research priorities are now focused on mapping where the gene occurs and testing if and how mcr-12 could mobilize.