ifidobacterium is a Gram-positive, anaerobic, branched rod-shaped bacterium. In the intestines, they ferment sugars to produce lactic acid. The B. longum genome codes for many proteins specialized for the catabolism of oligosaccharides. This bacterium also is able to use so-called "nondigestible" plant polymers or host-derived glycoproteins and glycoconjugates; it is thought that Bifidobacterium's ability to compete with other gastrointestinal bacteria and occupy a large percentage in the bacterial flora of the gastrointestinal region might be partly due to the large variety of molecules that it is able to use for energy (Schell et al. 2002). Bifidobacteria have a unique hexose metabolism that occurs through a phosphoketolase pathway. This pathway, called the bifid shunt, uses the key enzyme frutose-6-phosphate phosphoketolase (F6PPK) and is the generally used as a diagnostic test for this Bifidobacteria because it's not found in other gram-positive intestinal bacteria.