Where would you expect an obligate anaerobe to grow in a tube of fluid thioglycolate medium?

• A. At the top of the tube, where oxygen concentration is highest
• B. Just below the surface of the medium
• C. At the bottom of the tube, where oxygen concentration is lowest
• D. Evenly throughout the tube

Answer: (C)

Verified step by step guidance

1. Understand the nature of an obligate anaerobe: these organisms cannot survive in the presence of oxygen because oxygen is toxic to them.
2. Recognize that fluid thioglycolate medium is designed to create an oxygen gradient, with the highest oxygen concentration at the top of the tube and the lowest at the bottom.
3. Recall that the medium contains reducing agents that consume oxygen, creating an anaerobic environment towards the bottom of the tube.
4. Predict that obligate anaerobes will grow where oxygen concentration is minimal or absent, which is at the bottom of the tube.
5. Therefore, the expected growth location for an obligate anaerobe in fluid thioglycolate medium is at the bottom of the tube, where oxygen concentration is lowest.