Antibiotics have been used routinely in livestock for decades because they not only increase growth of animals, but they allow them to be kept packed into factory farms with unsanitary conditions without the usual risks of disease. The only problem is that we have known for almost as long that overuse of antibiotics creates antibiotic-resistant pathogens. The more resistant strains show up (some of which are caused by overuse of antibiotics in humans, too), the closer we get to reliving the pre-antibiotic era when people routinely died of infections that today we consider minor nuisances.
It has been 35 years since the FDA acknowledged the risk of treating healthy livestock with antibiotics. Yet, they have made little progress on regulating this practice, in part because of pressure from the livestock industry claiming that there was no evidence of the practice causing resistant human pathogens, even while some scientists argue that the danger of resistance spread may be greatly underestimated.
Fast-forward to the era of methicillin-resistant Staphylococcus arueus (MRSA), which at its peak resulted in over a quarter million hospitalizations and 20,000 deaths in the U.S. (though thankfully, the trend of hospital-acquired MRSA infection is currently being reversed, probably due to better hygiene practices). So far, the FDA has taken only the small step of banning one class of antibiotics, (a rule that was delayed and watered-down over three years by industry opposition) even as studies from other countries showed years ago that stopping usage of routine antibiotics in livestock reduces resistance to related antibiotics used in humans.
A new study has now clearly demonstrated that we are playing with fire when it comes to overuse of antibiotics in animals (Price et al., 2012). Researchers studied the evolutionary origin of the MRSA strain clonal complex 398 (CC398), which occurs in livestock. Their phylogenetic analysis of this strain revealed that it originated from a methicillin-susceptible S. arueus (MSSA) strain occurring in humans. This means that an antibiotic-susceptible strain in humans jumped to livestock, acquired resistance to antibiotics commonly used in both animals and humans, and is now jumping back to humans in its less-treatable form. The diversity of the 89 isolates of CC398 from four continents that they collected and analyzed “is suggestive of strong and diverse antimicrobial selection associated with food animal production.”
Their conclusion follows:
In this study, we provide strong evidence that CC398 originated in humans as MSSA and then spread to livestock, where it acquired resistance to methicillin and tetracycline. Genomic analyses presented here, in conjunction with previous epidemiological data, suggest that the jump from humans to animals was followed by a decreased capacity for human colonization, transmission, and virulence, yet livestock-associated CC398 has been linked to an increase in MRSA infections in northern Europe. Further research is required to characterize the full scope of the genetic changes associated with the shift from humans to livestock.
Sure, the bright side is that the MRSA that evolved in livestock appears to have reduced virulence in humans compared to the MSSA it came from. Further research on this process should indeed be done (Rosengren et al., 2010). What would be even better would be to do the research after a complete ban on non-therapeutic hormone use in livestock is in place (which many scientists support), so that disaster doesn’t happen before we’ve actually understood the mechanism by which it will happen.
Would a ban increase the price of meat and reduce the profits of agribusiness? Almost certainly somewhat (although according to the World Health Organization which studied the issue in Danish pig production, not much). But even if the rise in cost of meat is significant, it all works out for the best, because with Americans’ meat consumption per capita over 200 lbs per year, and its attendant heart disease and cancer risks which we are all paying for (whether we individually eat meat or not) through our health insurance premiums, more expensive, humanely treated, unmedicated meat would be a win-win for everyone. Fortunately, the trend in meat (especially beef) production is going down, but until the U.S. finally stops this insane practice, try buying local, free range, unmedicated meat for awhile, and see what you think. Eat less of it, enjoy it more, be healthier, and as an added bonus exert some consumer pressure away from risky and unhealthy agriculture.
Feel free to tell me I can peel your cheap, factory-farmed meat from your cold, dead fingers — right after you stop making me pay the medical bills you racked up before that last heart attack finally did you in.
Price LB, Stegger M, Hasman H, Aziz M, Larsen J, Andersen PS, Pearson T, Waters AE, Foster JT, Schupp J, Gillece J, Driebe E, Liu CM, Springer B, Zdovc I,Battisti A, Franco A, Zmudzki J, Schwarz S, Butaye P, Jouy E, Pomba C, Porrero MC, Ruimy R, Smith TC, Robinson DA, Weese JS, Arriola CS, Yu F, Laurent F,Keim P, Skov R, Aarestrup FM., 2012. Staphylococcus aureus CC398: Host adaptation and emergence of methicillin resistance in livestock. MBio 3(1).
Rosengren LB, Gow SP, Weese JS., 2010. Antimicrobial use and resistance in pigs and chickens: A review of the science, policy and control practices from farm to slaughter — executive summary. Can J Infect Dis Med Microbiol. 21(3):123-7.