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16, Jul 2026

Antibiotic resistance found in surprise source

Centre scientists have found a new source of antibiotic resistance in an unexpected place: polluted freshwater sediment in NSW.
Researchers at Macquarie University and The University of Sydney discovered a gene that makes bacteria resistant to polymyxin, a critical last-resort antibiotic used when others stop working. The finding offers an early warning for researchers and public health officials. The findings are published in Nature Communications
The gene, called mcr-12, is the first of its kind discovered outside a clinical, food or livestock setting. It is also the first to be characterised in a host outside the Gammaproteobacteria, the bacterial group that includes E. coli, and the first to be initially reported in the Southern Hemisphere.  Scientists discovered mcr genes only a decade ago but until now believed they were confined to bacteria from hospitals, patients or livestock.
‘Polymyxin-resistance genes are typically associated  with settings where there has been direct polymyxin exposure, so this discovery challenges our previous assumptions,’  says Dr Brodie Gillieatt, the lead researcher from Macquarie University.
Concerningly, the gene still made bacteria resistant when moved from its original host into other disease-causing bacteria, a problem if it were to reach a clinical setting.
Professor Amy Cain, from Macquarie University, 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 found alongside heavy-metal resistance genes, in sediment already contaminated by heavy metals, raising the possibility that metal pollution could help maintain antibiotic-resistance genes.
‘A contaminated site like this turns out to be a genetic reservoir doing something nobody was watching for,’ says Dr Gillieatt. ‘The pollution itself may be what is driving the resistance.  This means environmental management could play a role in slowing the spread.
‘Genes like this are likely circulating in wider environmental reservoirs, and we simply have not invested in looking for them until now. We need broader surveillance.’
Research priorities are now focused on mapping where the gene occurs and testing whether and how mcr-12 could mobilise.
Above and left: The site where the discovery was made.