Yesterday, I posted about how feral pigs might be responsible for the spinach-associated E. coli O157:H7 outbreak. A while back, I described the epidemic spread of a new strain of MRSA throughout pigs in Europe. What was puzzling to me was why this MRSA strain, found at forty to sixty-fold greater frequency than all commensal MRSA in humans hadn't entered the human population. A recent paper in Emerging and Infectious Diseases lays out one possible reason--this strain of MRSA does not grow well on retail meat (which is thought to be a major conduit of strains from the farm to humans):
A new methicillin-resistant Staphylococcus aureus (MRSA) clone related to pig and cattle farming was detected in the Netherlands. We investigated the extent of S. aureus presence in meat and found 36 S. aureus strains in 79 samples. Two strains were MRSA; 1 was multilocus sequence type 398, the clone related to farming.
In other words, compared to the S. aureus coming from the agricultural setting, the 'pig clone' ("ST398") sucks at surviving in the food chain (this is a good thing).
Thankfully, there's no such thing as evolution....
Article cited: van Loo, IHM, Diederen BMW, Savelkoul PHM, Woudenberg JHC, Roosendaal R, van Belkum A, et al. Methicillin-resistant Staphylococcus aureus in meat products, the Netherlands. Emerg Infect Dis [serial on the Internet]. 2007 Nov [date cited]. Available from http://www.cdc.gov/EID/content/13/11/1753.htm
A new methicillin-resistant Staphylococcus aureus (MRSA) clone related to pig and cattle farming was detected in the Netherlands. We investigated the extent of S. aureus presence in meat and found 36 S. aureus strains in 79 samples. Two strains were MRSA; 1 was multilocus sequence type 398, the clone related to farming