||Caption: Bacteroides thetaiotaomicron - rod-shaped, obligately anaerobic, gram-negative, saccharolytic bacterium. Bacteroides thetaiotaomicron is the most common bacterium found in the human colon / intestinal tract. It is an obligate anaerobic bacterium, which uses various polysaccharides as its source of carbon and energy. Polysaccharides (starch) are the primary form of carbohydrate available for bacterial consumption within the human colon / intestine. Bacteroides thetaiotaomicron is able to use amylose, amylopectin, and pullulan (all three forms of starch) in addition to malto oligosaccharides. B. thetaiotaomicron, being a major bacterium in the human intestine, has been a useful model for the study of human-bacterial symbiosis, as well as for its digestive abilities and potential breakdown of digested plants. Additionally, it is very important during the postnatal transition between mother's milk and a diet heavily consisting of plant starches. Bacteroides thetaiotaomicron is also the second most common infectious anaerobic, gram-negative bacterium. It is considered an opportunistic pathogen, frequently associated with peritonitis, septicemia, and wound infections. B. thetaiotaomicron is capable of causing very serious infections, such as intra-abdominal sepsis and bacteremia. It is resistant to antimicrobial agents, especially penicillin, which is a cause for major concern.