Bacterium Gained Drug Resistance Thanks to Antibiotics Used on Farms

Antibiotic resistant bacteria has long been a concern, but scientists reported yesterday that they had figured out just how the bacterium that causes invasive-skin infections acquired this immunity. It starts on the farm.

The research from the Translational Genomics Research Institute published in the journal mBio found that methicillin-resistant Staphylococcus aureus (MRSA) strain CC398 became resistant to antibiotics because of their overuse in livestock.

"Most of the ancestral human strains were sensitive to antibiotics, whereas the livestock strains had acquired resistance on several independent occasions," said Ross Fitzgerald of the University of Edinburgh in Scotland. The statement on the research says this implies that the bacterium picked up the ability to fend off antibiotics after it migrated into livestock.

Essentially, the researchers found that once treatable strains of the bacterium became resistant when it moved to livestock it was exposed to many antibiotics. It then made the jump back to humans and has been spreading since. MRSA can cause skin and other tissue infections, respiratory infections, and sepsis, which can have major health implications. CNN reports that MRSA caused 278,000 hospitalizations and more than 18,000 deaths in 2005.

(Related: Cops: Man tries to rob cafe by threatening to spread his Staph infection)

Scientific American has more from one of the study's authors:

“We can’t blame nature or the germs,” Paul Keim, director of TGen’s Pathogen Genimics Division and co-author of the study, said in a prepared statement. “It is our inappropriate use of antibiotics that is now coming back to haunt us.”

“The most powerful force in evolution is ‘selection,’” Keim said. “And, in this case, humans have supplied a strong force through excessive use of antibiotic drugs in farm animal production.”

The Union of Concerned Scientists estimated in 2001 that livestock farmers in the U.S. used 24.6 million pounds of antibiotics each year for non-therapeautic reasons. This practice was banned by the European Union in 2006.