A study conducted by scientists at the University of Oxford has found that the antimicrobial colistin, previously used as a growth promoter on pig and chicken farms in China, resulted in the emergence of Escherichia coli strains that are more likely to evade the body's initial defense mechanism.
"This is potentially much more dangerous than resistance to antibiotics," warned study lead author Craig MacLean, a professor of Evolution and Microbiology at Oxford. "It highlights the danger of indiscriminate use of antimicrobials in agriculture. We've accidentally compromised our own immune system in pursuit of producing fatter chickens."
The use of antibiotics has long been a contentious issue, with many experts warning that the widespread use of these drugs in livestock contributes to the rise of antibiotic-resistant bacteria. In recent years, there has been a growing movement to reduce the use of antibiotics in farming, with many countries introducing regulations to limit their use.
Despite these efforts, however, the new study suggests that antibiotic resistance continues to rise, posing a major threat to human health and global food security.
The significance of this research extends beyond current practices in livestock farming. The study suggests that the development of new antibiotics in the same class as colistin, known as antimicrobial peptides (AMPs), may carry a particular risk of compromising innate immunity. (Related: Agricultural waste could be contributing to the rise of antibiotic-resistant bacteria.)
AMPs are naturally occurring compounds produced by most living organisms as part of their innate immune response, which serves as the first line of defense against infection. Colistin, derived from a bacterial AMP, is chemically similar to certain AMPs produced in the human immune system. The excessive use of colistin in livestock farming during the 1980s contributed to the emergence and spread of E. coli bacteria carrying colistin resistance genes, leading to subsequent restrictions on the drug's agricultural use.
In the study, E. coli strains carrying a resistance gene called MCR-1 were exposed to AMPs known to play significant roles in innate immunity across chickens, pigs and humans. The bacteria were also tested for their susceptibility to human blood serum.
The researchers discovered that E. coli strains with the MCR-1 gene were at least twice as resistant to human serum compared to those lacking the gene. On average, the gene increased resistance to human and animal AMPs by 62 percent. Furthermore, the resistant E. coli strains were twice as likely to cause infections and kill moth larvae when compared to the control strain.
The findings of the study are likely to add fuel to the ongoing debate about the use of antibiotics in livestock farming. While the consequences of increased resistance are challenging to estimate, the study sheds light on a fundamental risk that has yet to be fully explored. MacLean noted that the danger lies in the potential evolution of bacterial resistance to AMP-based drugs.
Antimicrobial resistance poses a dire global threat, with the United Nations warning that superbugs could cause up to 10 million deaths annually by 2050. The pressing need for new antibiotics has sparked a growing interest in AMPs as potential solutions, including drugs based on human AMPs.
As the world grapples with the challenge of antibiotic resistance, it is clear that urgent action is needed to address this growing problem. Whether this will involve the reduction in the use of antibiotics in livestock farming, increased investment in research and development, or a combination of both remains to be seen.
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