Livestock are reservoirs for antimicrobial-resistant pathogens

A new study published in the journal BMC Medicine has traced how livestock systems in Nairobi, Kenya act as reservoirs for antimicrobial-resistant (AMR) pathogens and AMR genetic determinants which have the possibility to infect humans. The experts highlighted the importance of ecosystem-wide surveillance of AMR and helped detail how to avoid and manage the development of drug resistance in bacteria.

Alexander Fleming, the scientist who discovered the world’s first antibiotic, penicillin, has already warned many decades ago that misusing antibiotics could lead to AMR, showing that bacteria, viruses, fungi, and parasites often evolve rapidly when exposed to antibiotic drugs, and eventually no longer respond to these medicines. Thus, as a result of drug resistance, antibiotics and other antimicrobial medicines can become ineffective and infections difficult or even impossible to treat. Nowadays, AMR is a serious global problem, with scientists estimating that, unless the issue is tackled now, by mid-century one person may die every three seconds due to AMR.

“High-income countries can apply resources and large investments against AMR in ways which low-income countries can’t,” said study lead author Dishon Muloi, a research fellow at the International Livestock Research Institute (ILRI). “But AMR isn’t just a high-income problem or a low-income country problem. With the ease at which it can spread around the world, it’s everybody’s problem. So resistance in a community in Nairobi could actually mean clinical failures in a clinic in Hong Kong in two days or three days. We are not yet treating the problem with the urgency it needs, considering our connected world.”

One path by which scientists assume that AMR will develop is through the vast amount of antibiotics used in the livestock industry, where pathogens develop resistance and then spread to humans. The experts conducted a controlled epidemiological assessment of 99 households in Nairobi, Kenya, and sequenced the whole genomes of bacteria isolated from 311 human, 606 cattle, and 399 wildlife excrement samples. Then, by using statistical methods, they assessed the prevalence of AMR carriage and described the diversity and structure of AMR genes in distinct host populations around Nairobi.

The analysis revealed – in both animal and human isolates – 13-point mutations and 56 acquired genes which are known to confer resistance to nine different types of antibiotics. Moreover, the makeup of the AMR gene community did not seem to be related to the host species, but instead, AMR genes were often co-located, suggesting that multi-drug resistance could be acquired and spread in a single step. Finally, they found that the risk of AMR transmission across human-livestock interfaces is greatest when manure is improperly disposed of.

“Doctors should not just be thinking about the rise of AMR in humans, but in livestock and the broader environment, because what we’re seeing is that wildlife collect and move around with what they acquire from the environment,” said Muloi.

“This study shows how easily antimicrobial resistance genes move between humans and livestock in a crowded urban environment, underlining that if we are to beat the resistance problem, we will need a coordinated response across the medical and veterinary sectors,” concluded senior author Mark Woolhouse, professor and Chair of Infectious Disease Epidemiology at the University of Edinburgh.

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By Andrei Ionescu, Earth.com Staff Writer

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