Why do people eat these bacteria?

There are some very specific uses for these bacteria. Lactobacilli and related species are very susceptible to antibiotics. After a course of antibiotics for, say, bronchitis or a urinary tract infection, it is not uncommon for a person to develop antibiotic associated diarrhea. The destructive effect of antibiotics on Lactobacilli and other good bacteria of the colon may permit disease causing bacteria to multiply. One particular pathogenic bacterium, Clostridium difficile, is often acquired when visiting hospitals or other health care facilities. It is a very hardy bacterium which is more resistant to the bactericidal effects of most antibiotics than Lactobacilli. Treatment with specific antibiotics such as Metronidazole, Vancomycin, or Rifampin is needed to get rid of this bacterium. Clostridium difficile elaborates an endotoxin which damages the small blood vessels of the intestine. Ordinarily, the numbers of Clostridium difficile are suppressed to low numbers by the coexistence of the Lactobacilli in the colon. If the Lactobacilli are wiped out by antibiotics, the Clostridium multiplies wildly, and a larger population of Clostridia secretes a greater amount of the endotoxin, creating intense diarrhea and cramps or colitis with bleeding. Maintaining a healthy population of Lactobacilli in the colon may keep the Clostridia in check so that this does not happen.

It is not an unreasonable idea to take a few doses of Lactobacilli after a course of antibiotics in order to restore their numbers to the large intestine. The problem is that most people take too much of these bacteria. It only takes 3-4 doses of a probiotic to repopulate the colon after a person takes a course of antibiotics, and taking more than that can cause other problems. While there are trillions of bacteria in the large bowel under normal circumstances, the small bowel needs to be sterile for digestion to proceed properly. Bacteria in the small bowel interfere with the small bowel's digestion of food and may lead to symptoms of bloating, cramps, flatulence, or diarrhea. Continued use of probiotics can lead to small bowel bacterial overgrowth with these symptoms. Continuous usage of a probiotic, accordingly, is not a good idea. One would never guess that from some of the advertisements for probiotics on television.

Some authorities believe that ingesting probiotics regularly stimulates the immune system which, in turn, protects the body from other digestive diseases. There are some very specific instances where this might be so, but it is not a general principle. Some authorities believe that probiotics help improve irritable bowel symptoms and certain specific situations in inflammatory bowel disease. My experience with people who take probiotics continuously for weeks or months is that they have more indigestion than benefit from this practice because of the small bowel bacterial overgrowth problem.