A team of investigators have isolated colistin resistant Escherichia coli from a commercial poultry farm in China. Colistin is an antibiotic of last resort against certain bacteria.
In research published in Antimicrobial Agents and Chemotherapy, scientists found that E.coli from the chickens often carried multiple resistant genes, including one copy of the colistin-resistance gene mcr-1 and one copy of the resistance gene, mcr-3.
Lead author of the study, Dr Hongning Wang: “This study was originally designed to isolate strains carrying mcr-1 genes, but it is surprising that there are already strains carrying multiple mcr genes in chicken farms. Photo: Anna Frodesiak / Wikimedia
Discovery poses huge human health threat
The evidence was found as part of ongoing surveillance by researchers at the Key Laboratory of Sichuan Province, Sichuan University, who collected rectal swabs from randomly selected birds in multiple commercial poultry farms in China.
This is the first report of these 2 genes on a single plasmid and prompted deep concern from the lead author Dr Hongning Wang.
Dr Wang, Professor of Animal Disease and Prevention and Food Safety at Sichuan University, said: “The co-existence of mcr-1 and mcr-3 in E.Coli isolates may pose a huge threat to public health.”
Spreading resistant genes
Plasmids are generic elements that can jump from one bacterium to another, and sometimes from one species to another, often spreading resistance genes. The resistance genes were contained on a type of plasmid known as IncP. The researchers also found circular pieces of DNA bearing mcr-3, which were derived from IncP plasmids. These so-called circular intermediates often contain “insertion sequences” that encourage their integration into other plasmids, hastening spread of the resistance genes.
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A post-antibiotic era
Dr Wang added: “This study was originally designed to isolate strains carrying mcr-1 genes, but it is surprising that there are already strains carrying multiple mcr genes in chicken farms.
“The apparent spread of the same IncP plasmid with 1 or 2 mcr genes between different species and a patient, the hospital environment, and animal production is worrying,” he added.
The mcr colistin resistance genes were only discovered in 2016 and there are now 5 and some variants within the 5.
“It is time to let the public understand the serious consequences of the abuse of antibiotics. If the last line of antibiotics is breached by bacteria, we will find ourselves in the post-antibiotic era,” he added.