For these studies, we utilized two well-characterized clinical isolates: LAC (Los Angeles County), representative of the USA300 group of organisms and closely related to the dominant CA-MRSA clone associated with soft tissue infections and serious invasive disease in the Memphis area [1] , and MW2, a clinical isolate from a midwestern child with fatal CA-MRSA sepsis [4] , representative of the USA400 group of organisms that constitute the other main lineage of CA-MRSA isolates in the United States.