Ivan Parkin and Michael Wilson from University College London, UK, look at how to make hospital-acquired infections a thing of the past

MRSA (methicillin-resistant Staphylococcus aureus), Clostridium difficile, Acinetobacter  and Enterococcus  species - these microorganisms are now virtually household names, and with good reason. The organisms are responsible for hospital-acquired infections that lead to over 5000 deaths in the UK alone each year. They are an enormous burden on the healthcare system - around 10 per cent of admitted hospital patients in the UK develop an infection.

 

Staphylococcus aureus - one of the bacteria responsible for 5000 deaths in the UK alone each year

 

A pressing issue is that the bacteria are developing a resistance to antibiotics, and some strains don't respond to therapy at all. In a race to develop new classes of antibiotics before the bacteria develop resistance, it is clear that the bacteria are winning. An alternative and certainly more desirable way to reduce infections is to prevent them starting in the first place. This can be helped enormously by strict hygiene control; however, bacteria are quite evasive in avoiding complete destruction. 

Hospital surfaces, for example door handles, ward fabrics and plastics, can act as reservoirs for the microorganisms and so are implicated in many infections. To tackle these problems, scientists are looking for ways to make the surfaces permanently antimicrobial. The strategy involves either making surfaces that are very difficult for microbes to attach to, or to make surfaces that kill microbes on contact. 

One type of surface that prevents microbes from sticking to it is called the easy-clean surface. This works by stealing a trick from nature - called the 'Lotus effect' - where plants have developed water-repellent surfaces to keep themselves free of microbes and parasites. The surfaces cause water to form spheres that spin and roll across them, picking up microbes as they go. An alternative approach is to have a hard diamond-like carbon surface that microbes find very difficult to adhere to. 

To kill microbes on contact, scientists have developed two new coatings. Both use light to activate materials within them. The first is a hard ceramic based on titanium dioxide. When sunlight is focused on the surface, it generates reactive radical species that kill the microbes. The second is a soft polymer containing light-activated antimicrobial agents. The advantage of these light-activated coatings is that they kill microbes rapidly and are very effective with any form of visible light - including indoor lighting. Also, as these new coatings can kill microbes by many pathways using reactive oxygen species as the agents of destruction, it is unlikely that microbes will be able to develop resistance.

Surprisingly, going back to more traditional methods could also be very effective. Since the 1980s, it's been known that copper is toxic to microbes. Clinical trials revealed that brass, a copper-based metal, reduced microbes in a test against stainless steel. Despite its hygienic image and widespread use in hospitals, the stainless steel had no antimicrobial activity. So an act as simple as replacing stainless steel fixtures and fittings in hospitals, such as push plates on doors, with brass ones could have an effect.

Many antimicrobial coatings are already in use but have yet to be adopted within the healthcare environment. These include AgION, a coating that releases antimicrobial silver ions, and Microban, which is a polymer that contains a registered pesticide called triclosan. The problem with these materials is that they continually release antimicrobials into the environment, making it easier for microbes to build up a resistance to them. 

The ideal surfaces, then, should be permanent, hard-wearing and work under hospital conditions. The armoury of antimicrobial coatings available offers hope in the fight against hospital-acquired infections, yet despite this, we still need a strict hygiene regime in place too, or we give the bacteria a chance to win the war.

Read more in the feature article 'Antimicrobial surfaces and their potential in reducing the role of the inanimate environment in the incidence of hospital-acquired infections' in issue 23, 2009, of the Journal of Materials Chemistry.

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