An analysis of the various genomes revealed that ST398 most likely evolved from an antibiotic-sensitive strain of S. aureus that came from humans. Once it found a home in livestock, the genome sequences indicate this strain changed rapidly, acquired some new genes, and differentiated into many different types, including ST398, which is resistant to a few different antibiotics.
"Most of the ancestral human strains were sensitive to antibiotics, whereas the livestock strains had acquired resistance on several independent occasions," says Ross Fitzgerald of the University of Edinburgh in Scotland, who reviewed the paper for mBio. This implies that the bacterium picked up the ability to fend off antibiotics after it migrated into livestock, says Fitzgerald.
The fact that ST398 originally came from a human is significant, says Fitzgerald, because it shows that infection is a two-way street. "Intensive farming practices could promote the transfer of bacteria between different host species including humans to animals," says Fitzgerald. ST398's family tree shows that sharing bacteria with livestock could well mean that those bacteria come back to us with the ability to defeat antibiotics.
|Contact: Garth Hogan|
American Society for Microbiology