The inverted tube is able to trap any gas products. The indicator, phenol red will turn yellow below pH 6.8 and a darker pinkish-red above pH 7.4. If the organism metabolizes the carbohydrate, subsequent acid production will result in lowered pH. If the organism does not ferment the carbohydrate, the pH may remain neutral. Acid production produces a color change from red to yellow, indicating that the organism is capable of metabolizing the sugar in the tube. Fermentation of the sugar is indicated by a color change to yellow.
Gas is trapped in the durham tube, replacing the medium in the tube.
A bubble indicates gas production. No color change in the tube means that the sugar was not utilized by the organism. Glucose Fermentation Organism Test Result 1. Control Negative 2. S. aureus Acid 3.