Patients taking oral antibiotics are aware of the presence of good bacteria in their intestional tract by the unhappy side effect of the antibiotics on them. Gut bacteria are intimately involved in digestion and nutrition. Antibiotics kill many of them, among the thousands of species of bacteria inhabiting the pipeline from mouth to anus, interrupting normal, healthy digestive cycles and allowing destructive bacteria and fungus to flourish. The result often is diarrhea. Naturopathic doctors will routinely recommend that patients take supplements of flora and eat yoghurt, after a course of antibiotics, to help replenish devastated populations of good bacteria. The Wall Street Journal discusses recent reseach that indicates that sharing feces also accomplishes the same result. Research reported in 2003 found that patients suffering outbreaks of C. diff (Clostridium difficile), a dangerous bacterium in the gut normally kept in check by beneficial bacteria, after treatments with antibiotics were cured when they were administered feces from close, healthy relatives. (The feces were administered through a tube through the nose to the stomach.) This research has been confirmed by experiments on rats, who eat each other's feces. (Barbara Martinez, "Gut Reaction: 'Good' Microbes Under Attack", The Wall Street Journal, August 18, 2009, D3.)
I have four questions about the sharing of beneficial bacteria through sharing fecal material. First, could this research provide a clue to the relationship of cleanliness to health? Researchers have also discovered (if I recall reports of this research accurately) that children raised on farms have fewer illnesses (of some sort or other) than children raised not on farms. One explanation for this natural immunity is that farm families often drink unpasteurized milk. Pasteurized milk does not contain live bacteria and enzymes, which are destroyed by heat processing. It seems clear from a major study of children in Europe that children who consume raw milk have fewer allergies and asthma than children who consume pasteurized milk. Are healthy bacteria from farm animals being spread from ever-present manure on farms to milk to the children and giving them health benefits by populating their intestines? Another explanation involves the general presence of bacteria associated with manure on farms, not simply beneficial bacteria in raw milk. Probably the bacteria help develop acquired immunities in the children. Could the bacteria also be ingested and provide benefits in the intestines? Can so acquired bacteria yield acquired immunities? The possibility of such benefits is suggested by the long history of domestic agriculture, now nearly 10,000 years old, which provides sufficient time for an evolutionary relationship between domesticated animals, humans, and beneficial bacteria. Deleterious relationships between DNA from farm animals and humans, as in the creation of swine and avian flu viruses, certainly exist; why not beneficial relationships? After all, one of the most important cells in the body, mitichondria, is an example of an ancient symbiotic relationship between a bacterium or bacterial ancestor and human metabolism. There must be many other such relationships.
Second, there must be some DNA-produced relationship between an individual's immune system and good intestinal bacteria and intestinal health if it is fecal material from close family members that can rebuild intestinal flora. Family members share fecal material through everyday touching and contact through handling shared materials, such as tools and utensils. So the immune system must, in its management of beneficial bacteria in the body, be social, probably through DNA. There must be a DNA based function in the immune system that distinguishes between support for beneficial bacteria shared among cohabiting family members and rejection of bacteria from other human families that, though good for those families, would be harmful to another family.
Third, dogs eat feces from other dogs and animals. Everyone who has kept dogs on a farm has observed them regularly eating some animals' manure, e.g., horse manure. And they don't eat many other animals manure. We assume the dogs do this to acquire fiber for their gut. (The manure produces stool that are, to my observation, much easier for dogs to pass than stool produced in a pure protein diet.) Perhaps they are also acquiring beneficial bacteria they need, since, otherwise, dogs' natural diet is mainly meat protein. If such a function were proved for dogs, it would be indirect confirmation of a similar function in humans.
Fourth, cooking and cleanliness are obviously intended to reduce our contact with harmful bacteria. If cooking and cleanliness have long histories, it is probable that the line between beneficial and harmful bacteria is related to the practices of cooking and cleanliness. Yes?