Human Superbug Started On Farms

Pigs in a factory farm.Credit: <a href="http://commons.wikimedia.org/wiki/User:Maqi">Maqi</a> via <a href="http://commons.wikimedia.org/wiki/File:Pigs-lying.jpg">Wikimedia Commons</a>.

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It’s long been suspected that administering large amounts of antibiotics to livestock promotes antibiotic resistance.

Now a new paper in mBio describes how a particularly nasty strain of MRSA—the CC398 strain found primarily in pigs but also in cattle and poultry—likely did that. 

Sequencing the genomes of 88 closely-related strains of S. aureus, the researchers found the CC398 strain likely originated as a harmless bacterium living in humans, which acquired antibiotic resistance only after it migrated into livestock. From there it migrated back to humans, where it now causes skin infections and sepsis, mostly in farm workers.

So far the strain has not evolved the ability to transmit between humans.

From the paper:

The CC398 strain of MRSA, which appeared in 2003, is now commonplace in US livestock. 

Modern food animal production is characterized by densely concentrated animals and routine antibiotic use, which may facilitate the emergence of novel antibiotic-resistant zoonotic pathogens. Our findings strongly support the idea that livestock-associated MRSA CC398 originated as MSSA in humans. The jump of CC398 from humans to livestock was accompanied by the loss of phage-carried human virulence genes, which likely attenuated its zoonotic potential, but it was also accompanied by the acquisition of tetracycline and methicillin resistance. Our findings exemplify a bidirectional zoonotic exchange and underscore the potential public health risks of widespread antibiotic use in food animal production.

Last month the FDA announced new restrictions on antibiotics in livestock. But New Scientists reports these rules cover only 0.2 percent of antibiotics used on farms in the US.

The paper:

  • Price LB, et al. 2012. Staphylococcus aureus CC398: host adaptation and emergence of methicillin resistance in livestock. mBio 3(1):e00305-11. doi:10.1128/mBio.00305-11.

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You expect the big picture, and it's our job at Mother Jones to give it to you. And right now, so many of the troubles we face are the making not of a virus, but of the quest for profit, political or economic (and not just from the man in the White House who could have offered leadership and comfort but instead gave us bleach).

In "News Is Just Like Waste Management," we unpack what the coronavirus crisis has meant for journalism, including Mother Jones’, and how we can rise to the challenge. If you're able to, this is a critical moment to support our nonprofit journalism with a donation: We've scoured our budget and made the cuts we can without impairing our mission, and we hope to raise $400,000 from our community of online readers to help keep our big reporting projects going because this extraordinary pandemic-plus-election year is no time to pull back.

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