Which one of the following organism normally inhabits the healthy human oral cavity?

Members of the mycoplasma group that are pathogenic for humans include M. pneumoniae and U. urealyticum. M. pneumoniae is best known as the causative agent of primary atypical pneumonia (PAP), which may be confused clinically with influenza or legionellosis. It also is associated with arthritis, pericarditis, aseptic meningitis, and the Guillain-Barn5 syndrome. M. pneumoniae can be cultivated on special media and identified by immunofluorescence staining and "fried egg" colonies on agar. U. urealyticum (once called tiny, or T, strain) has been implicated in cases of nongonococcal urethritis. As the name implies, this organism is able to split urea, a fact of diagnostic significance. U. urealyticum is part of the normal flora of the genitourinary tract, particularly in women. Both M. orale and Mycoplasma salivarium are inhabitants of the normal human oral cavity. These species are commensals and do not play a role in disease. The only other species of Mycoplasma associated with human disease is M. hominis. A normal inhabitant of the genital tract of women, this organ ism has been demonstrated to produce an acute respiratory illness that is associated with sore throat and tonsillar exudate, but not with fever. M. fermentans is an animal isolate.