<P> Archaea are present in the human gut, but, in contrast to the enormous variety of bacteria in this organ, the numbers of archaeal species are much more limited . The dominant group are the methanogens, particularly Methanobrevibacter smithii and Methanosphaera stadtmanae . However, colonization by methanogens is variable, and only about 50% of humans have easily detectable populations of these organisms . </P> <P> As of 2007, no clear examples of archaeal pathogens were known, although a relationship has been proposed between the presence of some methanogens and human periodontal disease . </P> <P> Fungi, in particular yeasts, are present in the human gut . The best - studied of these are Candida species due to their ability to become pathogenic in immunocompromised and even in healthy hosts . Yeasts are also present on the skin, such as Malassezia species, where they consume oils secreted from the sebaceous glands . </P> <P> Viruses, especially bacterial viruses (bacteriophages), colonize various body sites . These colonized sites include the skin, gut, lungs, and oral cavity . Virus communities have been associated with some diseases, and do not simply reflect the bacterial communities . </P>

Where are germs cells located in the human body