Early gut bacterial colonization may reduce risk of developing eczema

Strains of a bacterium commonly found in skin infections may help to protect against eczema, according to new research in the British Journal of Dermatology.

Atopic eczema is extremely common, affecting around one in five children in the UK. It causes skin to become red, itchy, sore and sometimes infected. This can greatly impact on a child’s quality of life.

The term ‘atopic’ is used to describe a group of conditions which include asthma, eczema and hay-fever. These conditions are linked by an overreaction of the immune system to harmless substances in the environment, such as house dust mites, pet dander, grass and tree pollen.

It is believed that exposure to certain microbes matures the immune system, making it less likely to become overreactive and cause allergies.

Not being exposed to these microbes as an infant could potentially make a child more susceptible to reactions to them later in life if they are genetically prone to these sorts of problems. This is known as the ‘hygiene hypothesis’.

Having these microbes in the gastro-intestinal tract in early infancy seems to be especially protective against the development of allergy.

Staphylococcus aureus (S. aureus) is one such microbe – it is a bacterium commonly found in the normal skin flora (it lives on our skin)and also commonly colonizes the gut of infants, where it can reach quite high numbers.

Now scientists from Sweden have discovered the strains (genetic variants) of S. aureus that help to protect against the development of atopic eczema.

In the first part of this research, the scientists suggested that, whereas the rate of gut colonization by S. aureus does not differ between infants who subsequently develop atopic eczema or those who do not, strains of S.aureus from infants without eczema more often carry certain combinations of genes called adhesin and toxin genes, notably ebp, encoding elastin-binding protein, and the superantigen genes selm and seln.

Superantigens are toxins produced by S. aureus that are very strongly immune stimulating, and these toxins are commonly known as causing ‘food poisoning’.

However, infants colonized by these S. aureus strains have no increased problems with vomiting or diarrhea, as opposed to adults who consume the toxins, for example in food that has been infected by S. aureus.

The purpose of this latest study was to confirm these earlier findings, in a group of 64 infants. Swabs and fecal samples were taken to measure microbe colonization in the gut and in the nasal passage at the ages of three days, one, two, four and eight weeks, and at four, six, 12, 18 and 36 months.

12 infants developed atopic eczema and 52 did not, and the strains colonizing these infants were grouped accordingly. Echoing the finding from the first study, S. aureus colonization in the gutper se was unrelated to subsequent eczema development, however, gut S. aureus strains from the infants who remained eczema-free were more likely to carry the ebp gene and superantigen genes encoded by the egc (selm and seln), as compared to strains from children who developed eczema.

Nasal colonization by S. aureus was less clearly related to subsequent eczema development. Notably, the researchers restricted the analysis to strains found in the gut of the infants during the first two months of life, well before the onset of eczema, to exclude that the results were due to a change in gut flora secondary to the atopic disease.

Part of the reason this study is so interesting is that, up until now, S. aureus has been seen as the villain of the eczema story, as this bacterium tends to be found in infected eczema patches and is thought to aggravate the disease. This study shows that actually, it has a positive effect too, as early gut exposure to S. aureus can actually help prevent eczema developing.

A complex interplay of factors contribute to eczema – there is no one set trigger, but rather a host of biological processes that, in combination, cause the disease. Research like this is incredibly helpful in providing a clearer picture of these factors, as we still do not fully understand this common, sometimes debilitating disease.”

Nina Goad, The British Association of Dermatologists

The two groups of children used in the two studies were sampled five to seven years apart and from different geographical areas: the first in the city of Gothenburg and the second in a rural part of southwestern Sweden. The almost identical findings for the two cohorts lend credibility to the hypothesis that early mucosal colonization by certain types of S. aureus beneficially affects stimulation of the infant’s immune system in a manner that reduces the risk of eczema development.”

Dr. Forough Nowrouzian, Lead Author

20 percent of young children now suffer from eczema, which is thought to be four times as many as fifty years ago. Figures for 12 to 14 year olds suffering from eczema in Britain are thought to be among the highest in the world.

Incidence of atopic eczema has been increasing greatly in recent decades in industrialised countries for reasons that are largely unclear. For example, studies of eczema among immigrant populations coming to the UK from countries where eczema is less of a problem, show that their children are suffering to same degree as white, non-immigrant children. Therefore, as well as genetic factors, there is a strong environmental influence which appears to be important in young people.

Source: http://www.bad.org.uk/