Bacteria

Bacteria are single-celled microorganisms that can exist either as independent (free-living) organisms or as parasites (dependent upon another organism for life). They are commonly found in the air, soil and water. Bacteria thrive when moisture, moderate temperatures, and nourishment are available. Some, such as those in the human digestive tract, are benevolent. Others may be the source of disease.

Cleaning normally eliminates the organic food source, and, by inhibiting bacterial growth, controls odors they produce. It is unnecessary to attempt to destroy all bacteria found in the human environment, since the body has natural defenses. Bacterial control is most important in bathrooms or restrooms, kitchen or food preparation areas and medical facilities.

Reference:

MedicineNet.com