Our bodies are hosts to a variety of bacteria - on our skin, in our mouths and in our guts. Gut bacteria, for example, not only help us to digest food but also seem to prime our immune system to recognise substances (e.g. pollen, foodstuffs) that are not harmful. People in the west have less variety in their bacteria than those in tribes living traditional lifestyles. Family members typically have similar bacterial species to each other, but allergic individuals have less bacterial variety than other family members.
The womb is a sterile place so we get our first bacteria at birth, as we pass through the vaginal canal, which itself changes to more lactobacillus species (known to have a protective affect) prior to birth. Our bacterial levels are then augmented via breast milk, which contains up to 700 species of bacteria. Other bacteria are ingested with food and as we interact with gardens, fields and woodland. But modern life is reducing the number of species of bacteria in some individuals.
- An increasing number of babies (around 25% at present in the UK) are born by Caesarian section, but a Norwegian study found that such babies are 52% more likely to suffer from asthma.
- Babies who spend time in incubators and intensive care units after birth have different combinations of bacteria from those born vaginally.
- These babies tend to have low levels of actinobacteria (in those with asthma) and bifidobacteria (in those with eczema).
- Allergic individuals have high levels of enterobacteriaceae, which is commonly found in intensive care units.
- Antibiotics not only kill bacteria that cause illness, but also kill beneficial bacteria in the gut. The use of antibiotics in early life (especially in the first year) appears to increase the risk of developing eczema by 40%.
- We spend far less time outside (and in contact with a variety of bacteria) than in the past - perhaps as little as 15% a day.
- In paleolithic times, humans lived in small hunter/gatherer groups, perhaps as few as 20 to 30 individuals. With this size of population, only infections (e.g. intestinal worms) which did not kill the host would survive. By quietening down the immune system (which also became less sensitive to allergens), they would be tolerated and never completely eliminated. Crowd infections (e.g. measles) have taken their place but don't damp down the immune system.
Faecal bacteriotherapy (or faecal microbial transplant) is a recent treatment for recurrent C. difficile infections, and increasingly for colitis and irritable bowel syndrome; it is also being investigated as a treatment for some neurological diseases, such as Parkinsons. It is now being speculated that it may be useful following antibiotic treatment to repopulate the gut flora, and even potentially as a treatment for allergies.
A sample of faeces from a healthy individual is treated to separate the bacteria from the food waste. The bacteria are then given to the patient by enema, colonoscope, nasogastric tube or naso-duodenal tube. Non-related donors (tested for a wide range of bacterial and parasitic infections) are preferred to family members (who may themselves carry C. difficile). Ongoing research aims to identify the important bacterial strains and to grow these anaerobically in the lab.
What should we do? Well, vaginal birth and breast feeding are ideal but not always possible. Boost bacteria levels by eating food that stimulates bacterial growth (fruit and vegetables). Probiotics provide limited help (but are not a cure for existing allergies). Antibiotics should be used only when necessary. Get outside (gardens, parks, or the countryside) as much as possible for more exposure to all sorts of bacteria. If you have a garden, the more types of plant you have, the better.
BBC Horizon programme Allergies: modern life and me, August 2014 and BBC website article 26 Aug. 2014.
