Which statement about nonpathogenic bacteria is true?

• A. They do not cause disease in humans.
• B. They always cause disease.
• C. They are viruses.
• D. They are only found in soil.

Answer: (A)

Nonpathogenic bacteria are bacteria that do not cause disease in humans. They can be harmless or even beneficial, helping with processes like digestion or fermentation. They are not viruses; bacteria are single-celled microorganisms with characteristics different from viruses, so the idea that they are viruses is incorrect. They are not confined to soil; nonpathogenic bacteria live in many environments, including on the skin, in the mouth and gut, in water, and in foods. While they generally don’t cause disease under normal conditions, some bacteria can act as opportunistic pathogens if a person’s immune system is compromised or they invade normally sterile areas. Overall, the statement that they do not cause disease in humans is true.