Molecular analysis of the accessory gene regulator (agr) locus and balanceof virulence factor expression in epidemic methicillin-resistant Staphylococcus aureus

Potential relationships between virulence factor expression and transmissib ility were assessed in epidemic methicillin-resistant Staphylococcus aureus (MRSA) clones CMRSA-1 and CMRSA-3, A major subtype of CMRSA-1 exhibited no rmal transcription of RNAIII, which facilitates the induction of secreted v irulence factors and repression of colonization factor expression at high c ell density. However, these isolates characteristically did not express alp ha-toxin or protease and displayed a limited profile of secreted proteins. CMRSA-1 also expressed a novel cell surface glycoprotein and exhibited a un ique polymorphism within the accessory gene regulator (agr) locus, CMRSA-3 displayed attenuated activation of RNAIII transcription, which was consiste nt with its higher fibronectin-binding and coagulase activity relative to s poradic MRSA or CMRSA-1 (P = .05), low protease activity, and limited profi le of secreted proteins. Thus, the balance of virulence factor expression i n CMRSA-1 and CMRSA-3 favors the colonization phase of infection, and CMRSA -1 possesses unique genotypic and phenotypic traits.