— A newly developed vaccine might serve as a useful weapon against the drug-resistant superbug MRSA, researchers say. Tests in mice have shown that the vaccine can protect against multiple types of MRSA, which can cause fatal infections in humans.
Experts say the discovery of a broadly effective vaccine is especially important as more infectious MRSA strains have recently emerged. They also stress that patients with compromised immune systems face an ever-increasing risk of acquiring MRSA, or methicillin-resistant Staphylococcus aureus, while in hospital.
Olaf Schneewind at the University of Chicago, Illinois, US and his colleagues came up with the new vaccine by identifying the bits of genetic code that eight different S. aureus strains share. This genetic analysis revealed 19 proteins that can be found on the cell surface of all eight strains.
Researchers then tested what type of immune response each of these proteins could trigger in mice by injecting the proteins individually into the animals. Of the 19 tested, they selected the four protein types that elicited the greatest immune system reaction and combined them into a single vaccine.
Schneewinds team then injected this combination into mice. Three weeks later they exposed the mice to different types of MRSA. All mice that received the vaccine survived exposure to the virulent MRSA strain that causes community-acquired infections in humans. By comparison, 65% of the control mice exposed to the same strains died.
Also, while all of the control mice exposed to the hospital-acquired MRSA strain USA100 died within 36 hours, 60% of vaccinated mice survived this strain.
Researchers say that if the new vaccine proves effective in future trials, it might be given to people prior to having surgeries, such as hip replacements, to protect them against MRSA while in hospital.
Hospitals have come under fire recently for not taking the necessary steps to disinfect against MRSA, which can be found on the skin and in the nose. The cleanest looking hospital can be riddled with infection, says Tony Field of the Birmingham, UK-based organisation MRSA Support.
One recent study has found that MRSA causes 12,000 inpatient deaths each year in the United States alone. Doctors also fear that MRSA will become resistant to the very few antibiotics that currently work against it.
The increase in outbreaks of MRSA taking place outside hospitals means such infections may become a wider public health problem in the future. A vaccine would be vitally important under such circumstances, says Field.
Schneewind says that human clinical trials of other MRSA vaccines have had disappointing results. He believes his approach will work because, unlike previous vaccines, it uses multiple S. aureus proteins to trigger the immune system.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0606863103)