Which statement best describes the habitat of clinically significant clostridia?

• A. They are not found in soil.
• B. They are found in the colon and in soil.
• C. They are found only in soil.
• D. They are only in animals.

Answer: (B)

Clostridia are aerobic? No, they are obligate anaerobes that form durable spores. They thrive in soil where their spores survive for long periods, acting as a common environmental reservoir. At the same time, many clostridial species reside in the human and animal gastrointestinal tract, especially the colon, where they can be part of the normal microbiota or participate in disease processes when conditions allow spores to germinate. Because their ecology includes both soil and the colon, the statement that they are found in both places best describes their habitat. Saying they are not found in soil, or found only in soil, or only in animals, misses the full picture of their distribution.