Farm antibiotics blamed for MRSA resistance

24-Feb-2012 - Last updated on 24-Feb-2012 at 11:12 GMT

The Staphylococcus aureus (S. aureus) bacterium responsible for MRSA became drug-resistant when it jumped from humans to antibiotic-fed livestock, new research suggests.

Led by the Translational Genomics Research Institute (TGen), the study analysed the genetics of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in humans and animals from 19 countries on four continents, and concluded that the dangerous MRSA bacterium observed in livestock originated as MSSA in humans.

“The lineage appears to have undergone a rapid radiation in conjunction with the jump from humans to livestock, where it subsequently acquired tetracycline an methicillin resistance,” the report said.

TGen pointed out that the antimicrobial resistance developed by S. aureus in livestock is linked to the use of certain antibiotics in food animal production, including tetracycline and cephalosporin.

“Staph thrives in crowded and unsanitary conditions. Add antibiotics to that environment and you’re going to create a public health problem,” said lead author Dr Lance Price.

The report reads: “Our findings exemplify a biderectional zoonotic exchange and underscore the potential public health risks of widespread antibiotic use in food animal production.

“The tetracycline resistance gene was nearly universal among livestock-associated CC398 MRSA and MSSA isolates and completely missing from human-associated strains. Consequently, tetracycline use in food animal production is likely to select for livestock-associated S. aureus CC398 without differentially selecting for MRSA strains.”

TGen scientists stressed the need for further research to determine how exactly the bacterium underwent genetic changes by shifting from humans to livestock, but said that the results of this study were “suggestive of strong and diverse antimicrobial selection associated with food animal production”.

Dr. Keim, biology professor at Northern Arizona University, added: “We can’t blame nature or the germs. It is our inappropriate use of antibiotics that is now coming back to haunt us.”

The report, produced by researchers from 20 institutes around the world, was published this week in the journal mBio.