Vaccination Against Staphylococcus aureus.jpgStaphylococcus aureus is a major cause of life-threatening infections such as bacteremia and endocarditis. Unfortunately, many strains of this bacterial species have become resistant to certain antibiotics, including methicillin and amoxicillin. These strains are known as methicillin-resistant S. aureus (MRSA). Therefore, the prophylactic and therapeutic potential of antistaphylococcal vaccines is currently being explored with priority.

Staphylococcus aureus is a gram positive, ubiquitous bacterial species that is responsible for over 340,000 instances of infection that end in hospitalization and for over 40,000 deaths annually in the United States. One of the ways that S. aureus persists within the host, particularly on indwelling medical devices, is through a biofilm mode of growth that prevents clearance by antimicrobial agents and the host immune system. In order to resolve the infection, the nidus of infection (i.e. the indwelling medical device) must usually be removed.

Treatment

Hospital acquired infection is often caused by antibiotic resistant strains (e.g. MRSA) and can only be treated with vancomycin or an alternative. Until recently, infections acquired outside hospitals have been treated with penicillinase-resistant ß-lactams. However, many of the community associated (CA) staphylococcal infections are now methicillin resistant. Particularly in Georgia, Texas, and California, the prevalence of CA-MRSA is widespread. Over 60% of abscess isolates from the emergency department of an Austin, Texas hospital yielded MRSA. These organisms are uniformly resistant to penicillins and cephalosporins. The infections have been treated with combination therapy using sulfa drugs and minocycline or rifampin.

Vaccines

No vaccine is generally available that stimulates active immunity against staphylococcal infections in humans. A vaccine based on fibronectin binding protein induces protective immunity against mastitis in cattle and might also be used as a vaccine in humans. However, vaccine therapies represent a new and innovative approach in broadening the available clinical tools against the global health problem of community and healthcare-associated S. aureus bacterial infections.

Hyperimmune serum or monoclonal antibodies directed towards surface components (e.g., capsular polysaccharide or surface protein adhesions) could theoretically prevent bacterial adherence and promote phagocytosis by opsonization of bacterial cells. Also, human hyperimmune serum could be given to hospital patients before surgery as a form of passive immunization.

When the precise molecular basis of the interactions between staphylococcal adhesins and host tissue receptors is known, it might be possible to design compounds that block the interactions and thus prevent bacterial colonization. These could be administered systemically or topically.

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