<P> A number of types of bacteria, such as Actinomyces viscosus and A. naeslundii, live in the mouth, where they are part of a sticky substance called plaque . If this is not removed by brushing, it hardens into calculus (also called tartar). The same bacteria also secrete acids that dissolve tooth enamel, causing tooth decay . </P> <P> The vaginal microflora consist mostly of various lactobacillus species . It was long thought that the most common of these species was Lactobacillus acidophilus, but it has later been shown that L. iners is in fact most common, followed by L. crispatus . Other lactobacilli found in the vagina are L. jensenii, L. delbruekii and L. gasseri . Disturbance of the vaginal flora can lead to infections such as bacterial vaginosis or candidiasis ("yeast infection"). </P> <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>

Where do we not harbor normal resident microflora