Researchers Find Possible Approach for MRSA Vaccine

This colorized 2005 scanning electron micrograph (SEM) depicted numerous clumps of MRSA bacteria. Magnified 2390x. Credit: CDC/ Methicillin-resistant Staphylococcus aureus, better known as MRSA and commonly pronounced “MER-sah,” is a serious problem in hospital settings. Although this particular type of S. aureus bacteria does infect people outside of medical facilities (typically referred to as “community-acquired infection”) it is more serious in healthcare environments, causing potentially life-threatening infection. In 2005, more than 18,000 people died during hospital stays related to serious MRSA infection.

As bacteria continue to develop resistance to more and more antibiotics, the development of vaccines to prevent infection with resistant bacteria becomes more important. Now, researchers at the University of Chicago have identified a possible approach for the development of a vaccine against MRSA.

MRSA has proved difficult as a vaccine target because of its ability to suppress the body’s immune response. Most vaccines exploit the fact that the immune system will respond in a certain way in order to confer protection against future disease. Even natural MRSA infection, however, does not confer such future immunity, making vaccine development against it tricky.

Olaf Schneewind, PhD (professor and chair of microbiology at the University of Chicago) and colleagues focused on two clotting factors that MRSA utilizes in order to “hide” from the body’s immune system. After the bacteria enters the bloodstream, it creates abscesses in which to multiply. Inside these abscesses, the bacteria is protected from the body’s immune system and able to multiply; days later, the abscesses burst, and even more bacteria are released back into the bloodstream.

Schneewind and colleagues studied two clotting factors: coagulase (Coa) and von Willebrand factor binding protein (vWbp), both used by MRSA in order to create abscesses. The researchers demonstrated that mutant versions of S. aureus without Coa and vWbp are unable to create abscesses, and thus unable to multiply in great numbers. Then, by injecting mice with versions of the clotting factors purified from an E. coli strain, the researchers used the clotting factors as subunit vaccine antigens, prompting the mice’s immune systems to generate antibodies against them. When the mice were exposed to various S. aureus strains in the future, the antibodies provided some protection against disease.

Although this research is preliminary and it’s not known whether the same approach will work for humans, the work highlights a potential target for a MRSA vaccine. The researchers are already working to combine the clotting factor antibody approach with other methods their group has studied in providing protection against MRSA.

Sources and More Information

Cheng AG, McAdow M, Kim HK, Bae T, Missiakas DM, et al. 2010 Contribution of Coagulases towards Staphylococcus aureus Disease and Protective Immunity. PLoS Pathog 6(8): e1001036. doi:10.1371/journal.ppat.1001036

Centers for Disease Control and Prevention: MRSA Infections