Immunologists at Trinity College Dublin (TCD) have discovered a novel trick used by the bacterium, Staphylococcus aureus, to thwart the immune response. This has raised hopes that a vaccine that prevents deadly MRSA infections may have moved a step closer.

Since the 1960s, Staphylococcus aureus has become increasingly resistant to the main antibiotic used to treat it – methicillin – resulting in MRSA. This so-called superbug has become endemic in hospitals worldwide. In fact, an estimated 700,000 deaths occur every year as a result of infections against which antibiotics are no longer effective.

Despite significant efforts by pharmaceutical companies, a vaccine against MRSA has so far proven elusive. One of the key challenges in developing an effective vaccine against MRSA has been the bacterium’s immense capacity for manipulating and evading the human immune system.

However, the TCD immunologists, working with scientists from GSK, have found that the bacterium interferes with the host immune response by causing toxic effects on white blood cells. This prevents them from taking part in their infection-fighting role.

The research also showed, in a pre-clinical model system, that the toxicity could be lessened following vaccination with a mutated version of a protein specifically engineered to throw a spanner in the MRSA works. This suggests that one day, a vaccine could do the same thing in people.

“In this study, we have identified a mechanism by which a protein made by the bacterium, known as Staphylococcal Protein A (SpA), attacks and rapidly kills white blood cells. This protein has been widely studied for its immune evasion capacity and has a well-documented role in rendering antibodies raised against the bacterium non-functional.

“Here, we uncover a previously undocumented strategy by which SpA forms immune complexes through its interaction with host antibodies, that in turn exert toxic effects on multiple white blood cell types. This discovery highlights how important it will be for effective vaccines to be capable of disarming the effects of protein A,” explained Prof Rachel McLoughlin, of TCD’s School of Biochemistry and Immunology and the Trinity Biomedical Sciences Institute (TBSI).

She pointed out that as a society, “we are witnessing first hand the powerful impact vaccination can have on curbing the spread of infection”.

“However, on the backdrop of the Covid-19 epidemic, we must not lose sight of the fact that we are also waging war on a more subtle epidemic of antimicrobial resistant infection, which is potentially equally deadly,” she pointed out.

The research is published in the journal, mBio, and can be viewed here.