Emerging Antibiotic-Resistant Bacteria Strains Are Brewing In US Pig Factory Farms

In factory farms, where animals live in cramped conditions and the overuse of antibiotics is rife, antibiotic resistance can become turbocharged. Image credit: Alax Zaj/Shutterstock.com

An emerging public health threat is quietly brewing in factory farms of the US. New research has found that multi-drug resistant strains of Staphylococcus aureus are spreading between pigs, farmworkers, their families, and members of the surrounding community in North Carolina.

Antibiotic resistance is set to become one of humanity’s biggest problems of the coming century. The idea is that microbes can evolve mechanisms that protect them from the effects of antimicrobials, allowing bacteria to become resistant to antibiotics and turn into so-called “superbugs”. In factory farms, where animals live in cramped conditions and the overuse of antibiotics is rife, this process can become turbocharged.

Scientists at Johns Hopkins Bloomberg School of Public Health recently headed to rural eastern North Carolina – an area with concentrated industrial-scale pig-farming – to investigate the scale of antimicrobial-resistant bacteria transmission between pigs and humans. As reported in the journal Emerging Infectious Diseases, the team used DNA sequencing of bacteria to show that pigs were infected with S. aureus strains that had many genes that confer resistance to antimicrobial drugs commonly used in industrialized agriculture. 

On top of this, these drug-resistant strains were also found in humans linked to the farms. It’s widely believed that S. aureus and other bacteria often leap from humans into pigs at factory farms. Now it looks like this bacteria is jumping from humans to pigs, where it acquires resistance to antibiotics, and is then passed back to humans.

The researchers found that the same multi-drug-resistant S. aureus found in the pigs was also present in the farmworkers, their family members, and other residents living nearby. The study used DNA sequencing of 49 S. aureus collected from the noses of pigs, the farmworkers, and the surrounding community in rural parts of North Carolina. This revealed that all the S. aureus bacteria belonged to a grouping known as clonal complex 9 (CC9). Furthermore, all of the bacteria samples appeared to be closely related, suggesting they were recently transmitted between pigs and people.

The current risk of this problem is not yet clear, as the study didn’t look at disease among people in the affected communities. However, in a press release, the researchers note that one farmworker had reported a recent skin infection, and also carried a strain of S. aureus from the CC9 isolate in their nose.

Perhaps most worrying of all, it’s apparent that this problem is slipping under the radar of most scientists and public health authorities, not least in the US. 

"This CC9 is a novel and emerging subpopulation of S. aureus that not many people have been studying, apart from a few reports in Asia," Pranay Randad, first study author and a postdoctoral researcher in the Bloomberg School's Department of Environmental Health and Engineering, said in a statement

"In other countries, such as in Europe, we see a high level of coordinated research on this topic from a public health perspective, with open access to collect bacterial isolates from pigs raised on factory farms, but so far in the U.S. not as much is being done," Randad adds.

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