Cytolysins, superantigens, and pneumonia due to community-associated methicillin-resistant Staphylococcus aureus.

In a 2007 report of a collaborative study that analyzed data from 2005, the Centers for Disease Control and Prevention (CDC) stated that Staphylococcus aureus is the most important cause of serious and fatal infections in the United States [1]. Methicillin-resistant S. aureus (MRSA) strains are well recognized as posing substantial infection problems for hospitals, but in the last 15 years, community-associated MRSA (CA-MRSA) strains have emerged to become highly important causes of skin and soft-tissue infections, as well as septicemia and pulmonary diseases that are often fatal [2–4]. In 1999, there were 4 children reported who had pulmonary infection due to community-associated MRSA—identified as CDC USA400 by use of pulsed-field gel elec-trophoresis (PFGE)—and all 4 children died [2]. The MRSA isolates recovered from these patients had multiple secreted virulence factors, including cy-tolysins (a-toxin, g-toxin, Panton-Valentine leukocidin (PVL), phenol-soluble modulins [PSMs]) and superantigens (staphylococcal enterotoxin [SE] B or C). In 2003, CA-MRSA CDC USA300 isolates emerged, which were also associated with skin and soft-tissue infections , as well as life-threatening septice-mia and pulmonary diseases [3]. Their secreted virulence factors included cy-tolysins (a-toxin, g-toxin, PVL, and PSMs) and a superantigen (staphylococ-cal enterotoxin-like [SE-l] Q). A recent study suggests that some of these USA300 isolates also make a deletion-mutant form of toxic shock syndrome toxin-1 (TSST-1) [5]. Although not generally recognized , CA-MRSA CDC USA100 and USA200 isolates are also emerging. These isolates have multiple secreted virulence factors, including combinations of cyto-lysins (a-toxin, g-toxin, PVL, and PSMs) and superantigen TSST-1 (a significant emergent strain in this category has the following phenotype: for cytolysins, a-toxin Ϫ , g-toxin Ϫ , PVL Ϫ , and PSMs + ; as well as superantigen TSST-1 +). It is important to remember that methicillin-susceptible versions of these organisms with the same PFGE type exist and that these methicillin-susceptible strains produce the same types of infection. With the emergence of severe pulmonary diseases caused by CA-MRSA, investigators have assessed the roles of secreted virulence factors. These diseases most often occur after viral infection and in association with preexisting conditions such as asthma, and they represent highly important fractions of CA-MRSA infections. The most widely recognized diseases associated with lung infections include necrotizing pneumonia [2, 3], purpura fulminans [6, 7], and postviral toxic shock syndrome [8]. Cytolysins have been the most studied virulence factors in serious pulmonary infections , including those studied in the article by Hongo et al …