What is the function of the Durham tube in the Multiple Tube Fermentation Test?

The function of the Durham tube in the Multiple Tube Fermentation Test is to detect gas production. This small inverted tube is placed within a larger test tube during the fermentation process. When microorganisms ferment carbohydrates present in the test medium, they may produce gas as a byproduct. If gas is produced, it accumulates in the Durham tube, leading to the formation of bubbles or a gas layer. This observation is key for determining the metabolic activity of the microorganisms being tested and helps in identifying which bacteria can ferment the specific sugars present in the medium.

The other options, while related to water testing concepts, do not accurately describe the role of the Durham tube. Measuring pH levels and observing color changes are typically assessed using different methods or indicators, and checking sludge quality pertains to other aspects of wastewater analysis that do not involve the gas detection function of the Durham tube.