Oral microbiota. Coloured scanning electron micrograph (SEM) of a culture from a used toothpick. Fungi, bacteria (yellow) and a fungal hypha are all visible The human oral cavity hosts a complex microbiota comprised of an estimated 600 bacterial species and 100 fungal species. 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.