MRSA

What is MRSA?

MRSA is one example of the Staphylococcus family of common bacteria. We all carry some Staphylococci on the surface of our bodies. There are many strains, and many people naturally carry this particular strain (i.e. MRSA) on their throat, nose and skin. In general Staphylococci bacteria can cause a mild infection such as pimples and impetigo in a healthy patient. Occasionally, Staphylococci can get through the skin and cause serious infection elsewhere in the body such as:

• Tissue infections (cellulitis)
• Sepsis (infection of the blood)
• Pneumonia
• Endocarditis

The key point about MRSA is that it’s no more aggressive than other infections, simply more resistant to treatment.

Although originally used to describe bacteria which were resistant to the antibiotic meticillin, MRSA is now commonly used as shorthand for any strain of S.aureus that is resistant to one or more powerful antibiotics of the penicillin group used to treat serious Staphylococcal infections. Experts have so far uncovered at least 17 strains of MRSA, with differing abilities to spread between patients and cause infections and different degrees of immunity to the effects of various antibiotics.

The problem of MRSA initially appeared in patients being treated in hospitals but more recently has become a problem in the community too. However, this isn’t a spill-over of the hospital problem as community-acquired MRSA seems to have developed quite separately, involving different strains of S.aureus. In addition, community-acquired MRSA often causes infections in previously healthy individuals who don’t have the risk factors that hospitalised patients do.

One factor which may in part explain this may be because many of these community strains produce a toxin called the panton-valentine leucocidin (usually referred to as 'PVL') which increases their ability to cause infections.

Fortunately community-acquired MRSA usually responds to other non-penicillin antibiotics.

Some strains of MRSA can spread rapidly - these are known as epidemic MRSA (EMRSA) and during the 1990’s there were particularly problems in the UK with two of these strains - EMRSA-15 and EMRSA-16. These strains still account for a large number of cases of MRSA septicaemia (bloodstream infections).

Causes of MRSA

It's all about survival of the fittest - the basic principle of evolution. Bacteria have been around a lot longer than us, so they're pretty good at it.

There are countless different strains of a single type of bacteria, and each has subtle natural genetic mutations that make it different from another. In addition, bacterial genes are constantly mutating.

Some strains' genetic makeup will give them a slight advantage when it comes to fighting off antibiotic attack. So when susceptible strains encounter antibiotics they die, while these naturally resistant strains may prove harder to kill. This means the next time you encounter S.aureus, it's more likely to be one that has survived an antibiotic encounter, (i.e. a resistant one). Eventually, the strain becomes resistant to different antibiotics, even though they work in slightly different ways.

When you are prescribed antibiotics, you are advised to finish the entire course. If you don't do this, there's a chance that you'll kill most of the bugs but not all of them - and the ones that survive are likely to be those that have adapted to be more resistant to antibiotics.

Over time, the bulk of the S.aureus strains will carry resistant genes and further mutations may only add to their survival ability. Strains that manage to carry two or three resistance genes will have extraordinary powers of resistance to a range of different antibiotics.

The reason hospitals seem to be hotbeds for resistant MRSA is because with many vulnerable patients, infections are common and easily spread. So many different strains are thrown together with so many doses of antibiotics, vastly accelerating this natural selection process.

Why is MRSA so dangerous?

A century or more ago people knew that an infection was bad news and could rapidly kill a patient. But these days, since the rapid development of antibiotics after World War Two, we often take the power of antibiotics for granted, and expect them to work without question. MRSA is dangerous because it takes us back to the days when little could be done to stop an infection.

MRSA is particularly dangerous in hospitals. It’s a fact of life in the NHS that hospital patients are at higher than normal risk of picking up a S.aureus infection on the wards.

This is for two reasons. Firstly, hospital populations tend to be older, sicker and weaker than the general population, and therefore more vulnerable to infection. Secondly, conditions in hospitals involve a great many people living cheek by jowl, examined by doctors and nurses who have just touched other patients - the perfect environment for the transmission of all manner of infections. This is why there are strict hand-washing and hygiene measures when entering and leaving wards, and between seeing different patients.

Once these patients develop an infection they’re less able than a healthy person to fight it and urgent treatment with antibiotics may be critical. But because MRSA is resistant to many antibiotics, it may quickly overwhelm a weak patient, or cause a festering infection (for example in a wound or a joint implant) that causes tissue destruction and chronic disability.

Symptoms of MRSA

MRSA infections can cause a broad range of symptoms depending on the part of the body that's infected. These may include:

• Surgical wounds
• Burns
• Catheter sites
• Eye
• Skin
• Blood

Like any infection, MRSA often results in redness, swelling and tenderness at the site of infection. There may be suppuration (or the production of pus) and poor healing of wounds. General symptoms include fever, nausea and weakness.

Sometimes, people may carry MRSA without having any symptoms.

MRSA treatments

Antibiotics are not completely powerless against MRSA, but patients may require a much higher dose over a much longer period, or the use of an alternative antibiotic, often needing intravenous administration or with less tolerable side-effects, to which the bug has less resistance.

MRSA is just one of a number of infections causing major challenges for health workers, and some are concerned that the situation can only get worse. There is no doubt that there is an urgent need to develop new and better antibiotics and, more importantly, to work harder to prevent infection spreading and use the antibiotics we already have more efficiently.

There is some evidence that MRSA in hospitals is already decreasing, as a result of better protocols to deal with the bacteria and prevent infection developing (with strategies such as regular screening of patients and use of eradication treatments).

New superbugs

Scientists are haunted by the spectre of a bug resistant to all antibiotics, and there are some contenders brewing. For example, VRSA, or vancomycin-resistant S.aureus, has acquired resistance to a drug considered the last line of defence when all other antibiotics have failed.

The UK has seen several cases of GISA, or glycopeptide intermediate S.aureus, a kind of halfway house between MRSA and VRSA, which has developed a resistance to antibiotics of the vancomycin family.

Experts are also concerned a type of MRSA emerging in the community in the UK called Panton-Valentine leukocidin (PVL) MRSA. PVL is a toxin that kills white blood cells and causes extensive tissue death. Not all types of S.aureus that make PVL are dangerous or difficult to treat, as some are sensitive to meticillin, but PVL MRSA appears to be particularly virulent (i.e. it spreads easily).

Another infection causing problems in UK hospitals is Clostridium difficile (C. diff). It isn't a ‘superbug’ as it lives harmlessly in many peoples intestines, and can be treated relatively easily. However, it forms very hardy spores, which can survive for long periods in the environment, such as on floors and around toilets, and spreads in the air.

So many patients are exposed to it, and if they’re weak and vulnerable C. diff may cause severe illness. It typically develops when certain antibiotics disturb the balance of normal bacteria in the gut. Then C. diff takes over and the toxins that it produces can cause a serious gastro-enteritis.

Strategies to control C. diff spores in the hospital, such as rigorous cleaning with warm water and detergent to remove spores from the contaminated environment and the hands of staff, as well as careful use of antibiotics in those likely to be at risk, are the most effective way to reduce the risk of infection.

Combatting superbugs

The Government, NHS and health professions are trying to at least slow down the apparently relentless march of the bacteria. One of the main reasons behind their swift evolution into superbugs is the overuse of antibiotics, both in human and veterinary medicine.

Until recently, patients visiting their doctor with a viral infection might demand and be given an antibiotic prescription, despite the fact that antibiotics have no effect on viral infections. All those patients were doing was strengthening the communities of bacteria in their bodies.

Doctors continually try to curb antibiotic prescribing and take more time advising patients about the nature of infections, but it can be hard when many patients still expect antibiotics to be prescribed, often when not necessary, and consultation times are so pressured.

Hygiene is another tried and tested way of protecting the most vulnerable patients from the most dangerous strains. Hand-washing by staff between examining patients should be a must, and all staff and visitors entering wards and potentially contacting contaminated surfaces and transferring infection must adopt similar hygiene measures. All additional staff (maintenance, cleaning, administrative) are also in the same position and must follow the standard hygiene protocols.