Researchers have discovered that a strain of methicillin-resistant Staphylococcus aureus (MRSA) bacteria that humans contract from livestock was originally a human strain, but it developed resistance to antibiotics once it was picked up by farm animals. The findings, which appear in the online journal mBio on Tuesday, February 21, illustrate a very close link between antibiotic use on the farm and potentially lethal human infections.
MRSA is the well-known cause of a variety of invasive skin infections that can quickly turn life-threatening, but in 2003 a novel form of MRSA called ST398 emerged in livestock. Today, ST398 regularly infects farm workers and others who come into contact with infected livestock with any of several types of acute infections, including skin and soft tissue infections, respiratory infections, and bacteremia (also called sepsis). The strain can now be found in pigs, turkeys, cattle, and other livestock and has been detected in 47% of meat samples in the U.S.
It has been thought that overuse of antibiotics in livestock production could be fueling antibiotic resistance in bacteria, including S. aureus. In 2001, the Union of Concerned Scientists estimated that livestock producers in the U.S. used 24.6 million pounds of antibiotics per year for non-therapeutic purposes, a controversial practice that has now been banned in the European Union.
The study appearing in mBio draws a line between the exposure of S. aureus to antibiotics on farms and the development of a form of MRSA that can threaten human lives, a correlation that has long been suspected but has been difficult to study directly.
A team of researchers from the Translational Genomics Research Institute (TGen) in Flagstaff, Arizona, the Statens Serum Institut in Denmark, and several other institutions sequenced the genomes of 88 different S. aureus isolates that are all closely related to ST398 to det
|Contact: Garth Hogan|
American Society for Microbiology