What type of bacteria is often found in the human gastrointestinal tract?

Escherichia coli, commonly known as E. coli, is a type of bacteria that is frequently found in the human gastrointestinal tract. It plays a crucial role in the digestive process and is considered part of the normal flora of the gut. These bacteria help with the digestion of food and the synthesis of certain vitamins, including vitamin K. While some strains of E. coli are harmless, others can cause serious foodborne illnesses.

The other options mentioned do not typically reside in the gastrointestinal tract in a benign or regular capacity. Mycobacterium is more often associated with diseases like tuberculosis, while Staphylococcus is generally linked to skin-related infections and is not a predominant inhabitant of the intestines. Mycoplasma is a type of bacteria that can cause respiratory and urogenital infections and doesn't have a significant presence in the gut. Therefore, E. coli stands out as the primary and beneficial type of bacteria commonly found in the human digestive system.