A new study has shown that overuse of antimicrobials in livestock production has the potential to drive the evolution of bacteria, creating strains more resistant to the first line of the human immune response.
As this journalist has previously written: “Antibiotic resistance is a form of drug resistance whereby some sub-populations of a microorganism are able to survive after exposure to one or more antibiotics. In the last two decades, the rate at which bacteria are becoming resistant to current antibiotic treatments has substantially increased.”
This means there is an urgent need to develop new, effective antimicrobials. One solution is in the form of antimicrobial peptides (AMPs). The main use of AMPs, so far, has been in farming, especially in livestock production. Here farmers are seeking to control infections as well as using the chemicals as growth promoters.
This has led to concerns that agricultural AMP generates cross-resistant bacteria that could then overcome the human innate immune response. This is the finding that has emerged from University of Oxford studies.
To test the idea, the researchers used colistin, an AMP produced by a bacterium (Bacillus polymyxa) that is chemically and functionally similar to AMPs produced in animals. Colistin is a ‘last-line of defence’ for treating infections caused by multidrug-resistant bacteria.
The widespread use of colistin in livestock production has driven the spread of Escherichia coli bacteria carrying mobile colistin resistance (MCR) genes.
The research has found that bacteria with an evolved resistance to colistin, an antimicrobial widely used in farming, display resistance to compounds that are key components of human and animal immune systems.
The research involved exposing E. coli carrying an MCR gene (MCR-1) to AMPs known to play roles in innate immunity in chickens, pigs, and humans. The bacteria were also tested for their susceptibility to human serum. It was discovered that the MCR-1 gene increased resistance to host AMPs by 62 percent, compared with bacteria lacking the gene. It also stands that E. coli carrying MCR-1 are at least twice as resistant to being killed by human serum.
The consequence of the results are that farmed pigs and chickens could potentially harbour significant reservoirs of cross-resistant bacteria, of a type capable of fuelling future epidemics. The results demonstrated that use of bacterial AMPs in agriculture can generate broad cross-resistance to the human innate immune response.
The research has been published in the journal eLife, titled “The evolution of colistin resistance 1 increases bacterial resistance to host antimicrobial peptides and virulence.”
