|Description:||This image depicts two test tubes each having been filled with O/F glucose (dextrose) medium, and inoculated with an unknown oxidative bacterial organism. O/F glucose medium consists of agar, glucose, peptone and a pH indicator. Mineral oil had been added to the tube on the right in order to prevent air from interacting with the medium underneath.|
The organism can be identified as oxidative, or one that oxidizes glucose. Note that in the tube at right, sealed by its covering of mineral oil, which prevents oxygen, a molecule needed for the process of oxidation, from coming into contact with the bacterial-inoculated medium, there is no color change. This indicates that no metabolic reactions had taken place. However, in left test tube, its contents were allowed to come into contact with environmental oxygen, and oxidation of the glucose contained in the O/F glucose medium did occur, which caused the pH in the upper reaches of the medium to become acidic, thereby, causing the indicator in the medium to turn a yellow color.