Commensal Provokes Immunity to Protect against Skin Infection of Methicillin-Resistant .

Unlike USA300, a strain of community-acquired methicillin-resistant (MRSA), commensal () bacteria isolated from human skin demonstrated the ability to mediate the glycerol fermentation to produce short-chain fatty acids (SCFAs). Quantitative proteomic analysis of enzymes involved in glycerol fermentation demonstrated that the expression levels of six enzymes, including glycerol-3-phosphate dehydrogenase (GPDH) and phosphoglycerate mutase (PGM), in commensal are more than three-fold higher than those in USA300. Western blotting validated the low expression levels of GPDH in USA300, MRSA252 (a strain of hospital-acquired MRSA), and invasive methicillin-susceptible (MSSA). In the presence of glycerol, commensal effectively suppressed the growth of USA300 in vitro and in vivo. Active immunization of mice with lysates or recombinant α-hemolysin of commensal or passive immunization with neutralizing sera provided immune protection against the skin infection of USA300. Our data illustrate for the first time that commensal elicits both innate and adaptive immunity via glycerol fermentation and systemic antibody production, respectively, to fight off the skin infection of pathogenic MRSA.