Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains have emerged as serious health threats in the last 15 years. They are associated with large numbers of atopic dermatitis skin and soft tissue infections, but when they originate from skin and mucous membranes, have the capacity to produce sepsis and highly fatal pulmonary infections characterized as necrotizing pneumonia, purpura fulminans, and postviral toxic shock syndrome. This review is a discussion of the emergence of 3 major CA-MRSA organisms, designated CA-MRSA USA400, followed by USA300, and most recently USA200. CA-MRSA USA300 and USA400 isolates and their methicillin-sensitive counterparts (community-associated methicillin-sensitive S aureus) typically produce highly inflammatory cytolysins α-toxin, γ-toxin, δ-toxin (as representative of the phenol soluble modulin family of cytolysins), and Panton Valentine leukocidin. USA300 isolates produce the superantigens enterotoxin-like Q and a highly pyrogenic deletion variant of toxic shock syndrome toxin 1 (TSST-1), whereas USA400 isolates produce the superantigens staphylococcal enterotoxin B or staphylococcal enterotoxin C. USA200 CA-MRSA isolates produce small amounts of cytolysins but produce high levels of TSST-1. In contrast, their methicillin-sensitive S aureus counterparts produce various cytolysins, apparently in part dependent on the niche occupied in the host and levels of TSST-1 expressed. Significant differences seen in production of secreted virulence factors by CA-MRSA versus hospital-associated methicillin-resistant S aureus and community-associated methicillin-sensitive S aureus strains appear to be a result of the need to specialize as the result of energy drains from both virulence factor production and methicillin resistance.
Bibliographical noteFunding Information:
Supported by National Institutes of Health grants R01s AI74283 , AI73366 , and AR41256 ; U54- AI57153 ( Great Lakes Regional Center of Excellence in Biodefense and Emerging Infectious Diseases , where P.M.S. is a member); and contract N01 AI40029 to D.Y.M.L.
Disclosure of potential conflict of interest: P. M. Schlievert receives research support from the NIH and has provided legal consultation/expert witness testimony in cases related to streptococcal toxic shock syndrome. M. L. Peterson receives research support from the NIH and 3M. D. Y. M. Leung receives research support from the NIH/NIAID, the NIH/NIAMS, and Novartis Pharmaceuticals. The rest of the authors have declared that they have no conflict of interest.
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