In capnophilic incubators, carbon dioxide should be maintained between which ranges?

• A. 1% and 5%
• B. 5% and 10%
• C. 10% and 15%
• D. 15% and 20%

Answer: (B)

Capnophilic growth relies on a CO2 level higher than the ambient air to support organisms that require more CO2 for optimal growth and proper medium buffering. In practice, providing about 5% CO2, typically within a range up to 10%, best supports these bacteria by helping maintain the pH and mimicking the conditions of their natural environments (such as mucosal surfaces).

This 5–10% range is used because it elevates CO2 enough to promote growth for organisms like Neisseria, Haemophilus, and Campylobacter, without overshooting to levels that could disrupt the culture. Lower CO2 may hinder growth, while substantially higher CO2 isn’t routinely necessary and can alter culture conditions.