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Spotlight on: Anti-MRSA Composition

MRSA is a major problem in hospitals today and is currently very difficult to treat as MRSA bacteria are resistant to most types of antibiotics.  University of St Andrews is developing a new treatment which can prevent and treat MRSA much more effectively.

What is Staphylococcus aureus?

Staphylococcus aureus is a bacterium. It is often just called 'S. aureus' or 'staph'. These bacteria are often found on the skin and in the nose of healthy people (carriers) for whom S. aureus is harmless.

However, S. aureus bacteria sometimes invade the skin to cause infection.  S. aureus is a common cause of wound infections and of skin infections such as boils, pimples, impetigo, skin abscesses.

In some people, S. aureus can sometimes get into the bloodstream and travel to internal parts of the body to cause more serious infections. For examples, septicaemia (blood poisoning) , pneumonia (lung infection), osteomyelitis (bone infection), endocarditis (heart valve infection), etc. These serious infections are more likely to occur in people who are already unwell or debilitated, or who have a poor immune system.

What is MRSA?

MRSA stands for methicillin-resistant Staphylococcus aureus. It is sometimes known as a "superbug". There are various sub-types (strains) of S. aureus and some strains are classed as MRSA. MRSA strains are very similar to any other strain of S.aureus. That is, some healthy people are carriers and some people develop the types of infections described above.

Most S. aureus infections can be treated with commonly used antibiotics. However, MRSA infections are resistant to methicillin and also to many other types of antibiotics and consequently MRSA infections and MRSA carriers pose a major problem to hospitals.

MRSA has become much more common since the 1980s and MRSA is now the cause of over 4 in 10 bloodstream infections with S. aureus.

How serious is an MRSA infection?

MRSA strains of bacteria are no more aggressive or infectious than other strains of S. aureus. However, infections are much more difficult to treat because many antibiotics do not work. Infections with MRSA can sometimes become more severe than they may otherwise have been if the cause of the MRSA infection is not diagnosed early and antibiotics that are not effective are given at first.

What is the current treatment of MRSA infections?

MRSA infections are usually treated with antibiotics.  However, the choice of antibiotic is limited as most antibiotics will not work. Many MRSA infections can only be treated with antibiotics that need to be given systemically. The course of treatment is often for several weeks. Also, the risk of side-effects with the limited choice of antibiotics is higher than the more 'usual' antibiotics which are used to treat non-MRSA infections.

How is the new treatment different?

The new treatment developed by University of St Andrews is a combination of a peptide (ranalexin) with a bacteria cell wall-digesting protein (lysostaphin), which specifically targets and kills Staphylococcus aureus, including MRSA. The combination is synergistic meaning that these components are more active together compared to the components on their own. Resistance to new antibiotics can arise rapidly but when antibiotics are used in combination the opportunity for bacterial resistance is greatly reduced provided that, as with this treatment, the compounds act on different bacterial targets. Importantly the combination is synergistic against lysostaphin-resistant S. aureus and also vancomycin-intermediate resistant (VISA) isolates. Furthermore, unlike conventional antibiotics the combination kills non-multiplying bacteria.

The combination is highly efficacious in vivo in a rabbit model, ex vivo on the surface of human skin and when dried on the surface of catheter tubing. In a rabbit model, we have demonstrated that when the combination is impregnated into dressings and applied to MRSA-infected wounds for 5 days it reduces MRSA in these lesions by >99% compared to the untreated controls and wounds treated with the individual components alone. Moreover, the combination was more effective compared to vancomycin-treated animals. Thus, the combination can be used topically to treat MRSA-infected wounds.

Similarly, the combination demonstrated enhanced efficacy for reducing MRSA on living human skin compared to the individual components alone. Thus, the combination is an effective de-colonisation agent specifically capable of reducing MRSA carriage without adversely affecting the skin's normal protective microflora. Additionally, the combination is active on the surface of catheter tubing and can reduce the viability of MRSA biofilms meaning it has application as a coating for indwelling medical devices.

Applications

  • Topical agent to eradicate MRSA nasal carriage in pre-operative patients as an alternative to mupirocin.

  • Incorporated into dressings or applied topically to treat MRSA-infected wounds.

  • Anti-Staphylococcal coating for indwelling medical devices, such as catheters.

  • Treatment to specifically remove Staphylococcus aureus and MRSA from skin or other surfaces.

For further details you can download the Information Sheet from this page or email Alistair Main.

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