Anti-virulence paradigm for development of staphylococcal therapies

University of Minnesota Ph.D. dissertation. February 2010. Major: Social, Administrative, and Clinical Pharmacy. Advisor: Marnie L. Peterson. 1 computer file (PDF); xi, 150 pages, appendices p. 147-150. Ill. (some col.)Staphylococcus aureus is a major human pathogen capable of causing various diseases, from skin infections to life-threatening pneumonia and toxic shock syndrome (TSS). S. aureus exoproteins contribute significantly to S. aureus pathogenesis via causing inflammation, tissue disruption, and immune evasion. Antibiotics treat S. aureus disease by eliminating bacteria, but provide no protection from S. aureus exoproteins, once released. With the emergence of antibiotic-resistant S. aureus, new therapeutic options to treat/prevent S. aureus-associated disease are critical. Given most S. aureus diseases initiate locally on mucosal surfaces or the skin, it was hypothesized that S. aureus exoproteins that have pro-inflammatory and/or cytotoxic effects on epithelial cells, contributing directly to S. aureus pathogenesis. Therefore, anti-staphylococcal therapies that inhibit toxin production and/or prevent toxin effects on host cells could reduce or prevent S. aureus infections. A global approach was taken to characterize pro-inflammatory properties of exoproteins from two genetically close TSS S. aureus isolates, a pulmonary TSS isolate (MNPE) and a menstrual TSS isolate (CDC587), on epithelial cells. Cytolysins, alpha- and gamma-toxins, superantigens, and staphopain (protease) were determined as the most pro-inflammatory (via interleukin-8) to epithelial cells. MNPE, originating from skin, produced large amounts of alpha-toxin and SAgs, but little other virulence factors, whereas CDC587, a mucosal strain, produced gamma-toxin, small amounts of alpha-toxin, and large numbers of secreted virulence factors. These findings implied that pro-inflammatory S. aureus exoproteins play key roles in environmental selection and disease severity. As proof of principle, glycerol monolaurate (GML), a lauric acid monoester known to inhibit S. aureus exoprotein production and to have anti-inflammatory effects, was compared with its monoether, dodecylglycerol (DDG), as local anti-virulence agents to prevent S. aureus disease using a rabbit wiffleball abscess/TSS model. GML, but not DDG, significantly decreased TSST-1 and local inflammation (via tumor necrosis factor-alpha in the wiffleball and prevented rabbit death from TSS. In summary, these studies identified key exoproteins important in S. aureus mucosal pathogenesis and determined the potential for anti-toxin agents, such as GML, to treat and/or prevent S. aureus diseases. These studies also suggest the addition of anti-toxin components will improve the effectiveness of antistaphylococcal vaccines and immunotherapies