Bacteria (noun)

1. Microscopic single-celled organisms that can survive in a wide variety of environments.
2. Microorganisms that can cause disease in humans and other animals.

Origin:

New latin, from greek baktēria, plural of baktērion "small staff, rod", diminutive of baktēr "stick, rod".

Examples:

1. The water was tested for bacteria before it was used for irrigation.
2. Bacteria are responsible for the fermentation of yogurt.
3. The bacteria in the gut help to digest food.
4. The wound was infected with bacteria.
5. The bacteria in the soil are important for plant growth.