1. Half the dry weight of faeces consists of bacteria.
2. Some bacteria can digest substances that humans cannot, e.g. some carbohydrates.
3. Some bacteria produce vitamins that humans need such as vitamin K and some B vitamins.
4. The oesophagus, stomach and first section of the small intestine are mostly bacteria free due to the strong stomach acid and high level of digestive enzymes.
5. Best estimates put the actual number of bacterial cells in the digestive system at any one time at approximately 100 trillion (10¹⁴) cells.
6. The number of individual species is thought to be between 300 and 1000.
7. If you could remove all the bacteria in one persons digestive system the whole lot would probably have a mass of about 1 kg (2.2 lbs)
8. New research is being undertaken into whether patients suffering from Crohn’s disease or a Clostridium difficile infection may benefit from a transplant of faecal bacteria from a healthy donor.
9. The concept of treating faecal diseases with faecal matter originated in China where 4^th Century literature mentions using it to treat food poisoning and severe diarrhoea.
10. In the 1600s there is reference to using ‘Yellow soup’ made of faecal matter and water, which was drunk by the patient to treat food poisoning. Do not try this at home!
11. Sales of probiotic (‘friendly bacteria’) products in 2014 reached a global high of around $3 billion (USD).

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Why not set your students some Structured questions on Bacteria in the Human Digestive System?