Oral fungal microbiota. Coloured scanning electron micrograph (SEM) of a fruiting body of the fungus Aspergillus (from a human oral culture). The human oral cavity hosts a complex microbiota comprised of an estimated 600 bacterial species and 100 fungal species. In a study of fungal species Candida and Aspergillus are the most frequently observed genera (isolated from 100% of participants), followed by Penicillium (97%), Schizophyllum (93%), Rhodotorula (90%), and Gibberella (83%). Both mutualistic and pathogenic microbes reside in the mouth. Pathogens often exist on pellicile, coating the dental tissues (enamel, dentin, cementum) and forming a complex matrix, or biofilm, more commonly known as dental plaque. These pathogens primarily affect the teeth, causing dental caries, also known as tooth decay. Magnification: x2000 when printed 10 centimetres wide.