Antibiotic resistant gene found in Australian soil
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 Australian researchers, 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 MCR genes 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,” says the lead researcher.
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.
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.
Despite its low amino-acid identity to known MCR enzymes, MCR-12 confers polymyxin resistance by phosphoethanolamine transferase modification of lipid A.
Expression of mcr-12 in Pseudomonas spp. and Acinetobacter baumannii conferred polymyxin resistance, suggesting that mcr-12 is compatible between environmental strains and clinical pathogens.
“It highlights the role of environmental pollution in antibiotic resistance meaning environmental management may also play a role in slowing the spread,” says the author. “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 mobilise.
