... can you count how many various different parasites, viruses and bacteria live in the average person's colon? Do you think it's more than in a barrel of untreated sewage or less?

About 75 to 100 different kinds of germs live in each person's mouth -- of a total of 700 that collectively populate all human mouths, Paster says. Of these, scientists know the names of only about 300.

You have more bacteria in your mouth than cells in your body, says Paster, and a toothpick plaque sample would hold 10 million to 100 million cells.

He suggests you could help reduce halitosis by brushing not only the teeth, but also the tongue, twice daily, along with scraping the tongue and using oral care products containing zinc.

Bacteria are vital for the maintenance of human health, but some pathogenic bacteria also pose a significant health threat by causing diseases. Large numbers of bacteria live on the skin and in the digestive tract. Their growth can be increased by warmth and sweat. Large populations of these organisms on humans are the cause of body odor and thought to play a part in acne. There are more than 500 bacterial species present in the normal human gut and are generally beneficial: they synthesize vitamins such as folic acid, vitamin K and biotin, and they ferment complex indigestible carbohydrates.[6][7] Other beneficial bacteria in the normal flora include Lactobacillus species, which convert lactose and other sugars to lactic acid in the gut.[8] The presence of such bacterial colonies also inhibits the growth of potentially pathogenic bacteria (usually through competitive exclusion) and some beneficial bacteria are consequently sold as probiotic dietary supplements.[9]