Epidemiologic and Clinical Divergence of MRSA USA100 and USA300 in the United States

(MRSA) is listed by the World Health Organization as a priority pathogen posing a major worldwide threat to public health. Two lineages of MRSA predominate as causes of human infections in the U.S.: USA300 and USA100. Although they are most often grouped together as MRSA, these two lineages differ in pathogenetic mechanisms in important ways. The epidemic spread of these two dominant lineages has been problematic because of the multidrug-resistant profile of USA100 and the virulence of USA300, as well as their ability to adapt to both community and hospital environments. In this perspective, we examine what is currently known about their distinctive biology and the consequent differences in infections caused by these two main MRSA epidemic clones. The purpose of this perspective is to provide critical insights to the clinical microbiology community to stimulate further research to inform the design of new prevention and management strategies for MRSA.