Micrococcus luteus bacteria, composite image - stock illustration

Colonies of Micrococcus luteus bacteria on the surface of nutrient medium, photograph and computer illustration. These aerobic, Gram-positive bacteria are found in fresh water, in raw milk, and on mammalian skin. In humans, they are normally found living in the human mouth, the mucosal linings of the upper pharynx, and the respiratory tract. They are not generally pathogenic in humans, but can cause complications in those who are immunocompromised. These bacteria are capable of dividing in more than one plane, and often form tetrads (clusters of four).