Billions of bacteria live in the human mouth, about the same as the number of people on Earth, according to WebMD. Research shows a person's mouth contains over 700 species of microscopic bacteria, approximately the same number as in a dog's mouth, although human and canine bacteria are different.
Daily brushing, flossing and rinsing with an antiseptic mouthwash help reduce the types of germs that cause gum disease, notes WebMD. Individuals should avoid sharing personal items such as toothbrushes, drinking glasses and lipsticks to prevent transmitting germs, infections and viruses. One way people can avoid bacterial growth on their toothbrushes is to let them air dry after rinsing them with running water. People should replace their toothbrushes with new ones every three to four months or after recovering from illnesses.