Evolutionary History of Methicillin-Resistant Staphylococcus aureus

Studying the spread of antibiotic resistant bacteria, researchers were able to reconstruct the evolutionary history of MRSA. In order to do this, the researchers sequenced the whole genome of multiple MRSA bacterium from the mid-1940s before the invention and subsequent widespread use of methicillin. Using Bayesian phylogenetic reconstruction to infer the the timing of the emergence of the SCCmec element--a collection of several alleles that provide drug-resistance for the MRSA bacterium--researchers discovered that the exposure to methicillin did not drive the initial appearance of the SCCmec element, rather the widespread use of penicillin during the 1940s was the more likely to blame. Finally, the researchers note that horizontal gene transfer between MRSA bacterium is likely the cause for such a rapid evolutionary history of the species.

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--Leanne Chambers