Fatty acids are the energy source for the colonic mucosa cells. Some members, such as B. fragilis, can be pathogenic. Aerobic bacteria Escherichia coli E. coli are rod shaped bacteria representing members of the family Enterobacteriaceae , which are Gram negative, facultative anaerobes. These enteric bacteria can produce large amounts of gas during sugar fermentation. E. coli is a major facultative anaerobe inhabitant of the colon in humans.
Some strains can cause gastroenteritis.
Similar to E.coli, this group also represents members of the family Enterobacteriaceae . They are facultative anaerobic and, therefore, inhabit the human colon freely. They very seldom cause enteritis. Candida albicans is a normal member of the gastrointestinal tract, and in normal individuals, does not produce disease. Growth is suppressed by other microbiota.