Sydney – Researchers have identified a previously unknown gene that confers resistance to polymyxin, a last-resort antibiotic, in contaminated freshwater sediment in New South Wales. The discovery, published in Nature Communications, marks the first time such a resistance gene has been found outside clinical, food, or livestock settings and the first in the Southern Hemisphere.
The gene, named mcr-12, was detected in the bacterium Pigmentiphaga litoralis, a non-Gammaproteobacterial species. It remained functional when transferred to several pathogenic bacteria, raising concerns that it could spread to clinically relevant pathogens in the future.
Unlike previously known polymyxin resistance genes, which are typically associated with environments involving direct antibiotic use, mcr-12 was found in sediment contaminated by heavy metals. The researchers suggest that heavy metal pollution may help maintain antibiotic resistance genes in the environment.
“This discovery challenges our previous assumptions,” said Dr Brodie Gillieatt from Macquarie University, lead author of the study. “Polymyxin resistance genes are usually linked to settings with direct antibiotic exposure.”
Professor Amy K. Cain, also from Macquarie University, emphasised the importance of early detection. “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 findings highlight the role of environmental reservoirs in the emergence and spread of antibiotic resistance. The researchers call for broader surveillance of such genes beyond traditional clinical and agricultural settings.
The study was conducted by researchers from Macquarie University and the University of Sydney.
