Microbial Ecology and Dysbiosis in Human Medicine

Microbial ecology and dysbiosis are topics worthy of study. This review article will be the first of a two-part series that will discuss normal flora and threats to its ecology resulting in dysbiosis. Microorganisms are generally required to attain critical population increases before they threaten the host. The research on the role of bacterial microorganisms which are considered to be part of normal flora and their importance in inhibiting potential pathogens will be discussed. This article also explores potential threats to healthy microbial flora, including dietary influences, anxiety and depression, and pathogenic bacteria and fungi. Defense mechanisms and their role in preventing translocation of infection from the GI tract to distal sites are also discussed. The role of probiotics in keeping a balanced microbial flora will be the subject of a future article. (Alt Med Rev 1997; 2(3):202-209) Human Microbial Ecology The human body maintains a rich and diverse microbial flora. Virtually every surface of the body having contact with the outside world has been colonized by various bacteria and fungi. The term “normal flora” implies that the microbes in question live with us symbiotically and generally cause no harm. However, each individual’s dietary and lifestyle habits, environment, body chemistry, and immune system influence the floral balance of the body, and what is considered normal for one person may cause a pathogenic condition in another. The following discussion involves the various types of bacteria that colonize the oral cavity and gastrointestinal system, their metabolic effects upon each other and the body, and how their populations may be influenced by external factors such as diet, stress, antibiotics, and biotherapeutic agents. The mouth, nose, and throat are colonized by Actinomyces, Neisseria, Bacteroides, Lactobacilli, Fusobacterium, Streptococcus, Staphylococcus, Corynebacterium, spirochetes, yeasts and others. There are an average of 10 microbes per ml in saliva. Anaerobic bacteria colonize at the gumline and between the teeth. More anaerobic than aerobic bacteria are found in the mouth, and especially high numbers of Fusobacterium and spirochetes have been implicated in periodontal disease. Both Streptococci and Lactobacilli play a major role in dental caries by converting oligosaccharides from the diet into dextran and levan, which cause plaque formation on the teeth. Fluoride and vitamin B6 reduce the numbers of these bacteria in the mouth, reducing the potential for cavities. The stomach harbors few bacterial species, and those that survive the highly acidic pH of gastric juices are primarily acid tolerant Lactobacilli and yeasts which are constituents of the oral flora. Other bacteria that pass through the stomach are most likely destroyed by hydrochloric acid. Evidence for this is that the duodenum, the part of the small intestine adjacent to and