New research that is easily missed because of the increasingly unusual use of cc398 instead of the more usual st398. Both refer to the same troublesome strain.
Humans first, maybe, but the conclusion seems clear enough and implicates livestock, and by extension antibiotic use in livestock creating antibiotic resistant features, before spreading to humans. The public health risks are once again confirmed.
"Our findings strongly support the idea that livestock-associated MRSA CC398 originated as MSSA in humans. The jump of CC398 from humans to livestock was accompanied by the loss of phage-carried human virulence genes, which likely attenuated its zoonotic potential, but it was also accompanied by the acquisition of tetracycline and methicillin resistance. Our findings exemplify a bidirectional zoonotic exchange and underscore the potential public health risks of widespread antibiotic use in food animal production."
Full report ( mBio ) here