Pig-to-Human 'Superbug' May Be Due to Animal Antibiotics

By robert preidt

Livestock-associated staph infection underscores potential health problem, researchers say

TUESDAY, Feb. 21 (HealthDay News) -- Researchers who traced the evolution of a potentially deadly antibiotic-resistant bacteria strain that can jump from livestock to humans say their findings highlight the dangers of widespread antibiotic use in animal food production.

The international team of scientists studied methicillin-resistant Staphylococcus aureus CC398, also known as pig MRSA or livestock-associated MRSA, which most often infects people with direct exposure to swine or other livestock.

It's likely that MRSA CC398 originated as an antibiotic-susceptible strain in humans before it jumped to livestock, they said. Once in livestock, MRSA CC398 became a so-called superbug, resistant to two important antibiotics, tetracycline and methicillin, used to treat staph infections.

This resistance is likely caused by the widespread use of antibiotics in livestock to prevent infection and promote growth, said the authors of the study published online Feb. 21 in the journal mBio.

The findings reveal evolution in action, according to Paul Keim, one of the study authors and a professor and director of the Center for Microbial Genetics and Genomics at Northern Arizona University. He is also director of the pathogenic genomics division at the Translational Genomics Research Institute (TGen) in Phoenix.

"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. It is that inappropriate use of antibiotics that is now coming back to haunt us," Keim said in a university news release.

This strain of MRSA was discovered less than a decade ago but appears to be spreading quickly, according to study lead author Lance Price, a university faculty member and director of the Center for Food Microbiology and Environmental Health at TGen.

"Our findings underscore the potential public health risks of widespread antibiotic use in food animal production," Price said in the news release. "Staph thrives in crowded and unsanitary conditions. Add antibiotics to that environment and you're going to create a public health problem."