Study: Using antibiotics in agriculture can 'endanger human immune system’

Scientists have cautioned that the widespread use of antibiotics in agriculture has resulted in the rise of bacteria that are more resistant to the human immune system.The study reveals that the antibacterial colistin, which was used for decades as a growth booster on pig and chicken farms in China, resulted in the creation of E coli strains that are more likely to bypass our immune system's first line of defence.

Although colistin has been banned as a livestock food additive in China and many other countries, the findings raise concerns about a new and serious threat posed by antibiotic misuse.

“This is potentially much more dangerous than resistance to antibiotics,” said Prof Craig MacLean, who led the research at the University of Oxford told The Guardian.

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“It highlights the danger of indiscriminate use of antimicrobials in agriculture. We’ve accidentally ended up compromising our own immune system to get fatter chickens,” he added.

The findings may also have ramifications for the development of novel antibiotic drugs in the same class as colistin, known as antimicrobial peptides (AMPs), which the researchers believe may offer a special danger of limiting innate immunity.

Most organisms produce AMPs as part of their innate immune response, which is the first line of defence against infection. Colistin is based on a bacterial AMP, which bacteria utilise to protect themselves from competitors, but it is chemically similar to other AMPs produced by the human immune system.

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In the study, E coli bearing the MCR-1 resistance gene were exposed to AMPs known to play essential roles in innate immunity in chickens, pigs, and humans. The bacteria were additionally tested for their susceptibility to human blood serum.

Effects on human immune system

The researchers discovered that E coli bearing the MCR-1 gene were at least twice as resistant to being wiped out by human serum. In comparison to bacteria that did not have the gene, the gene improved resistance to human and animal AMPs by 62 per centon average. The study, which was published in the journal eLife, also found that the resistant E coli strain was twice as likely as the control E coli strain to kill moth larvae that were injected with the infection.

MacLean stated that it was impossible to predict how this would transfer into real-world consequences, such as the probability of E coli infection leading to sepsis and death.The predominance of these E coli strains has reduced dramatically since China restricted the use of colistin as a growth promoter, implying that these genes have extra "fitness disadvantages" for the pathogens. However, the data reveal a basic vulnerability that has not yet been thoroughly examined.

“The danger is that if bacteria evolve resistance to [AMP-based drugs], it could also make bacteria resistant to one of the pillars of our immune system,” MacLean told The Guardian.

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