Wednesday, 5 March 2014

MRSA dominates with the help of skin bacteria

There could be an explanation for how the most common strain of methicillin-resistant Staphylococcus aureus (MRSA) rapidly rose to prominence. Research published in mBio®, suggests that the strain recently acquired a number of genes from common skin bacteria that allow it to grow and thrive on the skin where other strains of MRSA cannot.

Since it was first identified in the late 1990s the USA300 strain of MRSA has undergone an extremely rapid expansion across the United States. It is now the predominant cause of community-acquired MRSA skin and soft tissue infections and has been implicated in MRSA outbreaks among professional football teams. The strain is genetically distinguished from other strains by a cluster of genes known as the arginine catabolic mobile element (ACME.)

Using phylogenetic analysis researchers have shown that the modular segments of ACME were assembled into a single genetic locus in Staphylococcus epidermidis (a relatively harmless bacterium typically found on human skin) and then horizontally transferred to the common ancestor of USA300 strains in an extremely recent event that coincided with the emergence and spread of this strain.

The researchers identified one ACME gene in particular, called speG, that conferred on USA300 strains the ability to withstand high levels of polyamines, compounds produced by the skin that are toxic to other strains of MRSA. Polyamine tolerance also gave MRSA multiple advantages including enhanced biofilm formation, adherence to host tissues and resistance to certain antibiotics, according to the study.

The findings suggest that these properties gave USA 300 a major selective advantage during skin infection and colonization, contributing to the evolutionary success of this clone.

For further details see:

P. J. Planet, S. J. LaRussa, A. Dana, H. Smith, A. Xu, C. Ryan, A.-C. Uhlemann, S. Boundy, J. Goldberg, A. Narechania, R. Kulkarni, A. J. Ratner, J. A. Geoghegan, S.-O. Kolokotronis, A. Prince. Emergence of the Epidemic Methicillin-Resistant Staphylococcus aureus Strain USA300 Coincides with Horizontal Transfer of the Arginine Catabolic Mobile Element and speG-mediated Adaptations for Survival on Skin. mBio, 2013; 4 (6): e00889-13 DOI: 10.1128/mBio.00889-13

Posted by Tim Sandle