Antibiotic use in livestock is increasing and leading to greater antibiotic resistance

We’ve talked extensively about antibiotic resistance on the blog but we haven’t focused much on the impact that antibiotics given to livestock have on humans. Farmers give low doses of antibiotics to farm animals in order to not only prevent illnesses in their animals, but also to promote growth within their livestock. Animals being produced for food account for about 80% of antimicrobial use in the United States and bacteria in the animals become resistant to these antibiotics in the same fashion that they do in humans. As antibiotic use rises, more bacteria are becoming resistant and these bacteria are passed from animals to humans through the environment, consumption, and direct contact. An international research team from Europe, India, Africa, and the United States mapped the global consumption of antimicrobials in livestock.

The results were published in the Proceedings of the National Academies of Science (PNAS) and compared the use of antibiotics in livestock in 2010 to the projected use in 2030. The authors found that the global use of antibiotics in livestock will increase 67% in the 20 years between 2010 and 2030. This is largely a result of an increase in demand for meat by middle class individuals in countries like Brazil, Russia, India, China, and South Africa (BRICS). These BRICS countries have shifted their livestock production systems to be more cost-effective by increasing the use of antimicrobials to ensure the health of their animals and to promote growth.

This increase in antimicrobial use in animals is a compounded annual growth rate of 2.6% annual which is almost three times the annual growth rate of the human population (.98%) during the same time period. The authors found that in 2030, if new regulations are not put into place, approximately 30% of all antimicrobial use will be accounted for in the livestock industry in China.

Many countries, and specifically those in the developing world, do not regulate the use of antimicrobials in livestock production. While directly linking antibiotic use in animals to drug resistant infections in humans is very complex, it can be inferred that increase in antibiotic use leads to antibiotic resistant bacteria, and we have seen evidence of this in practice. In countries like India, where bacterial diseases are very prevalent and a major public health concern, antibiotics are a key factor in fighting these illnesses.  Increased resistance to bacteria by increased use of antibiotics in farm animals will only increasingly prevent the effectiveness of antibiotics in humans.  

The study authors call for global action to decrease the use of antibiotics used in animals that are raised for meat consumption. While the authors do state that this analysis was based on limited available data, largely in developed nations, the global trends of antibiotic use in livestock is concerning. 

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

Insects may be contributing to antibiotic resistance

A review in Applied and Environmental Microbiology from earlier this year provided evidence for an elusive link in antibiotic resistance.  Livestock that are used for food are fed antibiotics to increase their body mass.  This creates a selective pressure for antibiotic resistance in their gut, and it is well known that many antibiotic resistant strains originate in these animals.  There is now mounting evidence that the antibiotic resistant strains of bacteria seen in humans are actually those same strains that originated from livestock.  How, though, is this antibiotic resistance being transferred from animals to humans?  According to this review: insects!

The authors detail studies showing that the feces of livestock animals contain many antibiotic resistant bacteria.  Other studies have shown that many insects found in farms can acquire these antibiotic resistant strains in their own guts by feeding off the feces of the animals.  The connection to humans is demonstrated in studies showing that when insects land on human food to eat, they can transfer their gut microbiome to these surfaces.  Thus the vector of antibiotic resistance between animals and humans is the guts of insects.  Furthermore, the authors show the same horizontal gene transfer that spreads antibiotic resistance in the guts of animals and humans also occurs in insects.

The authors of this article conclude that there should be an increase in pest control in farms, restaurants, and kitchens.  Antibiotic resistance is a growing problem, and small measures like keeping flies away from our food are certainly worthwhile.  Still, the most obvious solution is to outlaw antibiotic use in livestock all together, something that Europe has done since 2006.

Please email for any comments, news, or ideas for new blog posts.

The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.