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Antibiotic-Pumped Pigs May Be Source of MRSA

from the February 21, 2012 eNews issue
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Methicillin-resistant Staphylococcus aureus (MRSA), a particularly vicious staph infection that plagues hospitals, may have gotten its obstinate resistance to antibiotics from the routine of giving antibiotics to farm animals, according to a new study by researchers at Northern Arizona University. MRSA has become a major epidemic that has become more drug-resistant as it has spread. While most people normally have a bit of Staphylococcus bacteria on their skin, certain MRSA strains are lethal and difficult to treat when they get into the bloodstream.

According to the study, published by the American Society for Microbiology, the vicious new strains of MRSA did not develop in hospitals as previously thought; it appears the superbug started as a somewhat mild-mannered staph bacterium that jumped into the pig population. Later, when it eventually passed back to humans, it returned with a bad attitude and resistance to the major antibiotics generally used to treat staph infections. Researchers compared the genomes of humans, barnyard fowl and pigs from 19 countries to trace MRSA’s emergence, and the habit of giving livestock antibiotics as a matter of course has been credited with the development of this tenacious killer.

The big issue is that the common use of antibiotics in meat animals has killed off weaker versions of bacteria, while allowing stronger, antibiotic resistant strains to survive and reproduce additional difficult-to-kill offspring.

"The most powerful force in evolution is selection. And in this case, humans have supplied a strong force through the excessive use of antibiotic drugs in farm animal production," said Paul Keim, a co-author on the study and director of Northern Arizona University’s Center for Microbial Genetics and Genomics. "It is that inappropriate use of antibiotics that is now coming back to haunt us."

The CC398 strain of MRSA is in almost half of all the US food supply meat, according to the American Society for Microbiology. Most of the time the staph bacteria are killed when people cook their food well, but thoroughly washing counters and cutting boards after meat has touched them is a real priority.

"Our findings underscore the potential public health risks of widespread antibiotic use in food animal production," said Lance Price, NAU faculty member and director of the Center for Food Microbiology and Environmental Health at the Translational Genomics Research Institute. "Staph thrives in crowded and unsanitary conditions. Add antibiotics to that environment and you're going to create a public health problem."

According to the CDC, about 19,000 of these people died of MRSA infections in 2005. About 94,000 persons contracted their first serious MRSA infection that year, 86 percent of which while in healthcare facilities. A 2010 CDC study published in the Journal of the American Medical Association did show that health care facilities have been more successful in fighting MRSA since then. The number of invasive (life-threatening) MRSA infections declined 28 percent between 2005 and 2008, and rates of MRSA bloodstream infections fell almost 50 percent during the 10 years from 1997 to 2007.

At the same time, MRSA continues to be spread outside of health care facilities as well. Anytime large numbers of people live or work together in crowded conditions – dormitories, or correctional or athletic facilities – there is a greater risk for MRSA to spread quickly. Childcare workers and students who participate in wrestling are susceptible for instance. Locker rooms have been tagged as spreading grounds for these bacteria. It doesn’t just hit high schools either; even NFL players have picked up MRSA.

People should not panic, though. "It's a good idea to avoid that level of fear, because it's costly and it scares people unnecessarily," Elaine Larson, professor of epidemiology at Columbia University's Mailman School of Public Health. The best thing to do is take precautions when sharing facilities with large numbers of people. Wash clothes and duffel bags regularly after visiting the gym. Don’t share towels or razors or other items that touch the skin. Keep wounds covered.

With the advent of antibiotics more than half a century ago, scientists predicted the end of death and suffering from infectious diseases. During the past 30 years, however, we have witnessed the reemergence and geographical spread of well-known diseases, including tuberculosis, malaria, and cholera, often in more virulent and drug-resistant forms. Infectious diseases are the leading cause of death worldwide, and the third leading cause of death in the United States.

Doctors have taken great pains to warn their patients to take antibiotic regimens all the way through to the last pill, to ensure that all bacteria are killed and the few strongest are not left to live and breed. We listen, and then we hunt down new antibiotics to battle the superbugs and take care not to let the bugs get resistant to those too. Yet, while we work to fight off these killers in our hospitals and homes, we are systematically creating super bacteria on our farms – in the name of good health.