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Where superbugs come from: CDC report reiterates that misuse of antibiotics in agriculture plays a role

Carmen Cordova

Posted September 16, 2013 in Health and the Environment

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A CDC report released earlier today highlights the growing public health crisis that threatens our health. Superbugs or antibiotic resistant bacteria are increasingly a problem as people face infections that are more and more difficult to treat. These infections can include urinary tract infections, skin infections, and soft tissue infections that require longer treatment or become more serious after the first round of antibiotics fail. These infections, according to the CDC, occur most often outside of hospitals. Thus, the CDC report calls for responsible use of antibiotics and draws attention to the multiple reasons for the rise of superbugs that are leading to complicated and deadly infections. Those reasons include the use or misuse of antibiotics in human medicine and agriculture. 

As it has before, the CDC makes clear that animal as well as human use of antibiotics is contributing to the problem. The report issued adds to the extensive literature documenting the link between agriculture and antibiotic resistant bacteria. It also specifically identifies several resistant bacteria as posing a serious threat, which have been associated with antibiotic use in agriculture. And it’s not the only recent scientific publication to link livestock and hospital infections. Here are a few peer-reviewed articles that have recently made the link.

A recent study by Francois Lebreton and others found that some multidrug resistant Enterococcus faecium isolated from hospital infections have emerged from animal strains. E. faecium is normally found in the guts of animals, even ours. Like E. coli, it can hang out in our gut without doing any harm, but once it goes to other places like the urinary tract or an open wound, it can cause serious infections especially when it is resistant to multiple antibiotics (superbug!) and importantly, vancomycin resistant Enterococcus was identified as a serious threat by the CDC. The authors looked at 73 different E. faecium strains, including strains isolated from the guts of healthy people, hospital infections, the guts of animals (including livestock), and the guts of hospital patients. The team of scientists made several discoveries, among them:

  • Most E. faecium isolated from hospital infections are more related to E. faecium found in animals than in healthy humans.
  • E. faecium from animals and especially the E. faecium isolated from hospital infections mutated at a higher rate and more likely contained multiple antibiotic resistance genes – including vancomycin resistance (were superbugs). In contrast, most isolates from healthy humans contained at most one.

Several recent studies have also found evidence of MRSA (methicillin resistant Staphylococcus aureus – also identified as a serious threat by the CDC) in humans having origins in livestock.  A study by Laura Spoor and others looked at the origins of some  MRSA human isolates and found evidence indicating that livestock is one potential reservoir for pathogenic bacteria that can transfer to humans and eventually cause disease. Other MRSA studies linked to livestock have been highlighted in a Nature news story, and my colleague, Jonathan Kaplan, has drawn attention to these studies in a previous blog.

These studies add to a long line of evidence that agricultural misuse of antibiotics is contributing to the rise of antibiotic resistance bacteria that can cause infections that are increasingly difficult to treat. Today, the CDC has again reiterated this point and called for policies to improve the use of antibiotics in both humans and animals and for better tracking and monitoring of antibiotic use. My colleague, Mae Wu, writes here about the CDC report and the kind of policies that can help address the misuse of antibiotics in livestock.  

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Comments

Tim SSep 16 2013 04:51 PM

Great blog Carmen!

Edgar castroSep 17 2013 12:09 AM

Thank you very important information

Heithem BoukariSep 18 2013 05:02 AM

Are there no restrictions to antibiotic use in livestock in the US or Europe? Is it known if most of the superbugs originating from animals, made their way to humans via contaminated meat or contaminated crops? What kind of antibiotics are used in livestock (macrolides, b-lactames, aminoglycosides?).

C CordovaSep 18 2013 02:10 PM

There are some restrictions both in the US and in Europe. However, there is heavier regulation in Europe than in the United States. See the link for an overview: http://www.nrdc.org/health/abx-timeline.asp

Unfortunately, due to a lack of a good surveillance system with isolates to test from the livestock industry and hospitals, we don't have a good way of examining the origins of the strains that are actually making us sick. Specialized studies done by scientists like Lance Price and others are trying to make check for these links on a local level.
Currently, different classes of antibiotics are being used in livestock. According to the data provided by the FDA based on sales, aminoglycosides, cephalosporins, lincosamides, macrolides, penicillins, sulfas, and tetracyclines are used. The amounts differ, but all those classes are used.

Heithem BoukariSep 19 2013 03:40 AM

I am wondering if the FDA managed to keep the deadline imposed by US courts. Seems to me these guys are reluctant to save their citizens from resistant strains! U must have a strong agriculture lobby!

good job carmen and thx for the info!

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