In a series of thioglycolate broth tubes, which tube would show growth of an obligate anaerobe?

• A. No growth in the tube
• B. Growth only at the bottom of the tube
• C. Growth evenly throughout the tube
• D. Growth only at the top of the tube

Answer: (B)

Verified step by step guidance

1. Understand the oxygen gradient in thioglycolate broth: the top of the tube is rich in oxygen, while the bottom is anaerobic (oxygen-free).
2. Recall the oxygen requirements of an obligate anaerobe: these organisms cannot survive in the presence of oxygen and therefore grow only where oxygen is absent.
3. Analyze the growth patterns: growth only at the top indicates aerobic organisms, growth evenly throughout indicates facultative anaerobes, and no growth means no viable organisms or unsuitable conditions.
4. Identify that obligate anaerobes will grow only at the bottom of the tube where oxygen is absent, as they require an anaerobic environment.
5. Conclude that the tube showing growth only at the bottom corresponds to the obligate anaerobe's growth pattern in thioglycolate broth.