What does a Durham tube detect in fermentation testing?

A Durham tube is specifically designed to detect gas production during fermentation testing. When a bacterium ferments a sugar, it can produce gases such as carbon dioxide as a byproduct. The Durham tube is a small inverted tube placed within another test tube containing the fermentation medium. If gas is produced during the fermentation process, it will accumulate in the Durham tube and displace the liquid, forming a gas bubble. This visible presence of gas indicates that fermentation is taking place.

While pH changes, color changes, and temperature fluctuations can also occur during fermentation and may be assessed through other means or indicators, the primary role of the Durham tube is to provide a visual confirmation of gas production specifically. This makes it a key tool in identifying the metabolic capabilities of microorganisms, especially in determining their fermentative pathways.