Interview: Author Maryn McKenna

In her book SUPERBUG (read review), Maryn McKenna discusses the rise and spread of a new and terrifying microbe, drug-resistant staph known as “MRSA.” Fair Food Fight got a chance to ask McKenna some questions about the role of food, farming, and livestock antibiotics in MRSA’s spread.

FFF: Let’s start with “MRSA 101″ for newcomers to the topic. Please summarize three years of SUPERBUG research in 100 words or less: What does MRSA stand for, and why is the medical community freaked out by this bug?

McKenna: MRSA is an acronym for methicillin-resistant Staphylococcus aureus, and there’s a lot of information packed into that acronym. Staphylococcus aureus – most people just say “staph”- is one of the most common bacteria on the planet; about one-third of us walk around all the time with it on our skin and in our nostrils. Most of the time it doesn’t make us sick, because it adapted over millennia to live in and on us. Once it gets inside our bloodstreams though, through a cut or scrape or a surgical incision, it can be virulent, causing overwhelming bloodstream infections, bone infections, infections of the valves of the heart. “Methicillin resistance” is shorthand for the reality that staph has become resistant to most of the drugs that we use in everyday medicine, a range of dozens of drugs that were based in some way on methicillin, the first synthetic penicillin derivative. So when we say “MRSA,” what we’re really saying is that there is a very common bacterium that resides on many of us – about 1.5% of the population harbors MRSA – that can cause very severe disease, that is resistant to most of the drugs we use every day in medicine, and that is continually picking up additional resistance factors and additional ways to cause disease. (Oops. 244 words. Sorry.)

FFF: The implications of MRSA for hospitals, schools, prisons, and other dense, “incubator” populations is harrowing. But as a food and farming blogger, I was unnerved reading about MRSA in our food supply, particularly in US pig populations. Are consumers at direct risk from eating pork or other animal products that comes from farms colonized by MRSA?

McKenna: This is complex. There is a strain of staph that causes food poisoning – it’s adapted to produce a toxin once it gets into our guts – but MRSA did not develop out of that strain. What happens with “pig MRSA,” or MRSA ST398 to be technical, is more subtle. The risk is that the bug will be transferred to the meat at slaughter, and then come home with buyers. If you then handle that raw meat in your kitchen, it is possible that you will transfer the bacterium to your skin or to your nostrils. It would then join the population of drug-sensitive staph or MRSA that resides on your body, leaving you at potential risk for an infection at some unpredictable future date. Because bacteria exchange resistance information very easily, it could also transfer its resistance pattern, which is different from that in hospital or community MRSA, to your own staph population, producing an unpredictable new strain.

FFF: Is there a difference in “organic” versus “conventional” farming practices, as far as MRSA’s spread is concerned?

McKenna: There’s a team at University of Iowa whose discovery of MRSA ST398 in pigs in Iowa is told in the book. Subsequently, they went on to compare the prevalence of MRSA ST398 on organic and conventional-confinement farms in Iowa and Illinois. On the conventional farms, 24% of the pigs carried MRSA. On the organic farms, none did.

FFF: You referenced a Korean study that had examined MRSA found in milk (12 positives of 894 samples), sourced from cows with mastitis. Should consumers be worried by a study like that?

McKenna: It’s not unusual for mastitis – teat infections, basically – to be caused by drug-sensitive staph. MRSA was definitely unusual. I would worry about it if I were a raw-milk drinker, but I suspect the heat-processing that happens to most milk would zero out the risk.

FFF: Let’s talk antibiotic resistance. Advocates of conventional agriculture and/or “Big Ag” claim that no proof exists that antibiotic use in livestock contributes to antibiotic resistance in humans. Are they right?

McKenna: That depends on how you define proof. It is true that no one has ever, experimentally: given an antibiotic to a farm animal; fostered the development of resistance in that animal; slaughtered that animal; fed the meat of that animal to a selected human; and documented the acquisition of a resistant infection in that human. You can see it’s not an experiment that anyone is likely to do.

But epidemiologically – which is to say, in a population sense – the connection has been demonstrated numerous times. There’s a section of SUPERBUG that runs through all the studies, which date back to the 1970s. Myself, I think MRSA ST398 makes this case beautifully, because it was first found in pig farmers and the pigs they owned, before spreading into health care workers and then into people who had no contact with farming. There was a new study just two weeks ago identifying ST398 infections in Canadians who had no contact with livestock or farms.

In Europe, this connection is taken for granted. Several European countries have enacted bans on certain agricultural antibiotics that are close analogs of drugs used in humans; those governments believe that using the drugs in animals will encourage the development of resistance that will make the drugs useless for humans.

FFF: What role do you believe that livestock antibiotics might play in growing resistance to antibiotics? You mentioned that just as problematic as overcrowding and poor health conditions in mismanaged CAFOs (confined animal feedlot operations) is “what those animals leave behind.” Care to elaborate?

McKenna: Super simply, the issue is that resistant organisms created on a farm don’t stay on a farm. They leave the farm with the animals sent to slaughter, and also in the animals’ manure, which is usually held in lagoons. Animals don’t “use up” 100% of the antibiotics they’re given – we don’t, either – so in the manure there are likely to be active ingredients of antibiotics, as well as near-infinite numbers of bacteria both resistant and drug-sensitive. That turns the manure lagoons into giant reactor vessels for the development of resistant bacteria. And there’s good research that resistant bacteria in manure lagoons can leave the lagoons via groundwater, in dust on the wind and on the feet of flies.

It’s important to note that responsible farms treat their manure lagoons to reduce the pathogenic bacteria in the manure, such as E. coli, so that some portion of the manure can be used as fertilizer, or can be transported in a less risky manner. But reducing the population of disease-causing bacteria doesn’t zero out the problem of resistance, because live bacteria can pick up the free DNA of dead bacteria and acquire their resistance patterns.

FFF: Have you looked at Rep. Louise Slaughter’s bill, the Preservation of Antibiotics for Medical Treatment Act? What’s your take on a legislative approach to curtailing antibiotic use?

McKenna: I don’t want to be cast in the role of a lobbyist, so I’ve refrained from endorsing any legislation in the same way that I’ve stayed away from endorsing any products. (Despite pleas; every week I kill blog comments that are nothing but ads.) But here’s the thing: The public health establishment works very hard to reduce the likelihood that people will take antibiotics without medical supervision or when they are not sick, because both of those contribute to the development of resistance. Yet what we want to bar in humans, we allow freely in animals – and every year in the US, animals collectively receive more antibiotics than humans and are subject to much less surveillance. That math doesn’t add up.

FFF: Let’s end on a hopeful note. What can people do to protect themselves from MRSA infection?

McKenna: There are some simple things that we can do, and some things we should ask institutions to do.

What we can do: Wash your hands, or carry an uncomplicated hand sanitizer, one without extra antibacterial ingredients. Don’t pester your doctor for a prescription if he or she says you don’t need it. Vote with your dollars, if you can afford it, and buy meat that’s raised with minimal or no antibiotics. Pester health care workers to wash their hands. Ask questions about why your kids no longer have to shower after school sports.

What we can ask for: Make MRSA a national priority. It’s astonishing that a disease that kills 19,000 Americans a year, sends at least 7 million to the doctor or emergency room, and costs billions of dollars in extra health care spending isn’t considered a bigger deal. We should ask public health to count it better, and we should ask health care to show some leadership and stop its infighting over competing infection control strategies. And in farming, we really should pay more attention to how food animals are raised.