The link between Alzheimer's and gum disease is oral bacteria. In the oral cavity, bacterial species include "P. gingivalis", "F. nucleatum", "P. intermedia", and "T. forsythia". Six oral treponema spirochetes have been examined in the brains of Alzheimer's patients. Spirochetes are neurotropic in nature, meaning they act to destroy nerve tissue and create inflammation. Inflammatory pathogens are an indicator of Alzheimer's disease and bacteria related to gum disease have been found in the brains of Alzheimer's disease sufferers. The bacteria invade nerve tissue in the brain, increasing the permeability of the blood-brain barrier and promoting the onset of Alzheimer's. Individuals with a plethora of tooth plaque risk cognitive decline. Poor oral hygiene can have an adverse effect on speech and nutrition, causing general and cognitive health decline.