Microbiology: A Systems Approach 4th Edition by Marjorie Kelly Cowan

Exercise 31

You're Outnumbered
They're everywhere, and they outnumber you 10 to 1. They are your microbiota. The thought of bacteria living on and in your body may make you squeamish, but these compatriots are vital to your health. Take the microbiota in your gut, for example: There are approximately 10 14 bacteria, archaea, and fungi living in your gut, accounting for about 1,100 different species, with about 10 10 cells per gram of feces. There are also about a billion viruses per gram of feces. The gut microbiota is a complex ecosystem comprised of numerous genera including Bacteroides, Clostridium, Streptococcus, Lactobacillus, Bifidobacterium, and others. These organisms play an important role in your health: from helping to digest food, to producing vitamins and amino acids, to stimulating the immune system, to protecting you from harmful pathogens, to even having an influence on your behavior.
Some recent studies have shown that the gut microbiota can have an influence on obesity. Scientists have found that the gut microbiota in obese individuals can extract more energy from the diet that is stored as fat. Other studies have shown that obese individuals have higher levels of Lactobacillus species than nonobese populations. In studies with mice, scientists demonstrated that a change in diet from a low-fat, plant-based diet to a high-fat, high-sugar diet shifted the population of gut microbiota within a single day, favoring the microbiota that influence increased fat storage.
What is the connection between gut microbiota and type II diabetes
What other human conditions can be influenced by gut microflora
In a recent study, the fecal composition of normal, healthy adult males was compared with that of adult males with type II diabetes. Scientists used PCR to analyze the 16S rRNA of the gut microbiota, and found that patients with type II diabetes also had elevated levels of bacteria from the phyla Bacteroidetes and Proteobacteria. Bacteria from these phyla are gram-negative, and this study suggests that the lipopolysaccharide outer membrane of these organisms may induce inflammation in the gut that could play a role in the development of type II diabetes.

Yet another study suggests that multiple sclerosis (MS), an autoimmune disease that attacks the myelin sheath of nerve cells, may be triggered by gut microbiota. Scientists found that mice raised without gut microbiota and then colonized with certain intestinal bacteria developed MS-like symptoms. Researchers still need to determine if a faulty immune system overreacting to gut bacteria is the cause of MS or if a specific organism triggers the autoimmunity.
What happens when your gut microflora is disrupted