Although banning the use of growth-promoting antibiotics in animal feed has helped slow the spread of antibiotic-resistant bacteria, the bans alone may not be enough to stop the spread of these bacteria, according to research from the University of Oxford.
A 2017 ban on growth-promoting antibiotics in China led to a 90% reduction in colistin consumption, according to the study. But the spread of antibiotic-resistant bacteria did not follow suit, prompting researchers to take a closer look, said Craig MacLean, a professor of microbiology at the University of Oxford.
The genes that enable bacteria to resist antibiotics are typically costly for bacteria — that is, they cause the bacteria to grow more slowly, MacLean said. Outside the presence of antibiotics, microbiologists expect the faster-growing, antibiotic-susceptible bacteria to out-compete the antibiotic-resistant strains. This should reduce the prevalence of antibiotic-resistant bacteria with time as antibiotics are removed from the environment, MacLean said.
But MacLean's team found certain strains of bacteria possess copies of a mutated gene for antibiotic resistance that does not come with the same drawbacks associated with the original versions of the gene. This has allowed bacteria such as E. coli to retain their antibiotic resistance without losing ground to competing bacteria that lack the gene, MacLean said.
MacLean remains opposed to the idea of using antibiotics to promote faster growth in livestock; there is clear evidence that doing so accelerates the spread of antibiotic-resistant bacteria and leads to infections in humans that are far more difficult to treat. But what his research shows, MacLean said, is that world leaders can't expect antibiotic bans alone to stop these bacteria from spreading. Other, more active solutions — such as developing bacteriophages that are engineered to target antibiotic-resistant bacteria — will be required.
“I don't think it's too late” to stop the spread of antibiotic-resistant bacteria, MacLean said. “I also don't think there will be a silver bullet solution to antibiotic resistance. This is a very complex problem, and there isn't going to be one thing that solves it. The silver bullet way of thinking is 70 years out of date.”
