Antibiotic Resistant Staph Bacteria: MRSA

The Use of antibiotics in livestock and the possible connections to the emergence of a super bug.

Published: March 27, 2009. You may have read that in 2005, there were 18,000 known deaths in the US that resulted from a type of Staph bacteria, Methicillin-Resistant Staphylococcus Aureus (MRSA), pronounced mer-sa. MRSA (Staph) is resistant to broad-spectrum antibiotics, and has recently been discovered in pigs (and farm workers), on farms in Iowa and Illinois. You may also have read that more people died from MRSA than died of AIDS, over the same period of time.

While that information may be accurate as a whole, the relationship between MRSA deaths (in general) and the swine strain (in particular) are quite misleading. MRSA causes more than one type of disease depending upon its strain. There are many Staph strains of MRSA, those widely associated with community outbreaks; and those associated with outbreaks in hospitals. There is one main type of MRSA found to be associated with swine and swine workers (MRSA ST398), and it has only recently been identified here in the US.*

In a phone interview today, I spoke with the author of a ground-breaking study to survey the incidence of swine MRSA on a select number of farms in Iowa and Illinois. Tara Smith, Associate Professor with the University of Iowa’s Department of Epidemiology, and her team, conducted this pilot study on US swine, and swine workers. The results of her survey showed a substantial prevalence of MRSA ST398 on one farm production system, and a high degree of spread not only through the general swine population, but also to the swine workers where the strain was identified. This is the first study to document the presence of MRSA ST398 in the US, though it has been previously identified on farms in Canada, the Netherlands, and Denmark.

As there are a number of bacterial strains that fall under the umbrella of MRSA, along with many different disease symptoms, MRSA ST398 (in the US) is not known to be associated with any human disease. However, a study conducted in the Netherlands has documented cases connecting ST398 with human illnesses, in some case, quite serious ones.

The community associated strains (MRSA ST398 falls into this group) can produce a wide array of human symptoms from skin rashes, and raised pimples, that may develop into more serious instances of bacterial meningitis, sepsis (blood poisoning), and bacterial pneumonia. Typically, community associated strains are more virulent in nature than the hospital associated strains. In general MRSA Staph are of particular concern to health officials because of their broad-spectrum resistance to antibiotic treatment. Some (MRSA) strains are resistant to all but the last line of defense antibiotics, and can be life threatening even with those treatments.

At the present time, there are more questions about MRSA ST398 on farms, and in meat, than we know as answers. Since our public health agencies appear to be taking a wait and see approach, there are no comprehensive studies underway addressing the broader potential health concerns. What is the connection, if any, between antibiotic use in livestock and the emergence of MRSA in animals and humans? Does MRSA ST398 pose a risk to humans, and if so, to what degree?

MRSA: Antibiotic Resistant Bacteria, Pigs, and Human Illness

Antibiotics are essential to the livestock industry, and certainly serve a legitimate, and essential purpose in protecting the health of animals, and by extension farm workers, and those of us who consume meat products. Why, beyond actual treatment for disease, is there a need to rely on these critically important drugs for non-therapeutic use (except in limited circumstances, for limited periods of time) when antibiotic resistance is such a serious world-wide concern? Is there a substantial link between widespread antibiotic use with livestock, and a growing antibiotic resistance found in humans?

Toward the end of our conversation, I asked Dr. Smith about what may follow next from her research study. With an enthusiastic laugh, she responded:

Oh, we have lots of next steps. At this point, that’s what is great about the research, we really have more questions than answers, right now… That’s our next direction of research, to really understand a little more about this particular strain [ST398], and see if it’s really a cause for concern as far as human disease goes, or its more of a concern as far as there being a lot of people out there who are carrying Staph, that have the Methicillin-Resistant genes, that could combine with other potentially more virulent human species of Staph.

*ST398 has been the main type associated with pigs, but other strains have been found in pigs in other countries. Dr. Smith informs me of a group in Canada led by Scott Weese that has found a different MRSA type, one that is connected with the hospital-associated strains.


  1. says


    Funny you should say that. I had a similar question, drawing an analogy with the problem of identity theft, a completely different topic but with possible parallels. Many individuals have been warned about protecting their own identities, not carelessly providing that information to other parties. Yet, from time to time, you read about huge financial institutions whose computer databases (with millions of complete financial records stored on individuals) becoming hacked, and the data stolen. Is it the individual or the large financial institution that is more to blame for identify theft?

    What also struck me about the research for this post, is the practice of using antibiotics, not for therapeutic proposes (to treat animal illnesses), but for preventing disease (before they occur), and sub-therapeutic use to increase the bulk of the animals. None of these issues were investigated in Tara Smith’s study (that was outside their scope) but it does make me wonder how much non-therapeutic use occurs, and how it may be stopped.

  2. maryn says

    There’s a lengthy archive of ST398 stories and research at the SuperBug blog – been covering this for more than a year in preparation for a book.

    In the “labels” column (lower right), choose “ST398″ for a search confined only to that strain, or “food” or “animals” for wider searches.

  3. Nicole (aka June1) says

    Thanks, Fred, for the story.

    My mother, who is seven years into Alzheimer’s, lives in a care facility. This January, the staff noticed a strange sore that turned out to be MRSA. She was hospitalized for a few days, to test for sepsis and treat the growing wound.

    After two months, the sore is healing, though tests show she still has MRSA–I think the term used was “colonized.” We’ve been told it could be nothing to worry about, or that it may resurface later. If it returns, it may not be something she can fight.

    In the past decade, I’ve noticed that my doctors don’t hand out antibiotics very easily–at least compared with how my sinusitis was treated fifteen years ago. But what good does that do if we don’t look at the whole picture, such as the use of antibiotics in pig farms?

  4. Pat Gardiner says

    Congratulations on a well balanced article dealing with a difficult subject.

    Alas, however, the risks are real enough, both sides of the Atlantic now.

    I have spent almost decade on this disaster, day after day: there at the beginning, with pigs and in pig country when the horror story started.

    We decided on a self-sufficient lifestyle and walked into a nightmare.

    There is little doubt that MRSA in pigs has been leaking into the hospitals for some years.

    There was a nasty mutation to a porcine circovirus in Britain in 1999 which caused an epidemic that required huge quantities of antibiotics to handle the consequences.

    MRSA in pigs was the result, usually the ST398 strain.

    The Dutch picked up the problem about four years ago and commendably made everything they knew public.

    Both circovirus and MRSA epidemics have now travelled the world along with accompanying cover-ups. It is quite a nasty situation – now coming to light in the USA.

    MRSA st398, mutated circovirus and various other unpleasant zoonotic diseases have now reached American pig farms.

    The people exposing the scandal in the US are to be commended.
    I travelled in 2005, at my own expense, to warn your people of problems on the horizen, but obviously was ignored.

    I have extensive records available to anyone researching the link and can often answer general questions quickly and accurately.

    In view of your well balanced approach, I imagine that you may feel difficult to publish my comments on your blog. I can understand that. If so, keep my comments by you for use later.

    Pat Gardiner
    Release the results of testing British pigs for MRSA and C.Diff now! and

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