Chapter 5, Section 5-1, Observations and Interpretations, Exercise 1
Here is a tip:
Bromothymol blue dye is used as an indicator for O-F test.
Uninoculated test tube gives green color as the medium is neutral, and the color of the bromothymol blue dye remains unchanged.
Escherichia coli are fermenters that produce an acid end-product, which changes the pH [potential of hydrogen] of the medium and turns the color of the bromothymol dye into yellow.
Kocuria rosea are oxidative bacteria that oxidize sugar in the presence of oxygen only to produce a yellow color.
Alcaligenes faecalis are non-saccharolytic bacteria. They are not able to metabolize carbohydrates present in the medium, and the color of media in both aerobic or anaerobic conditions is green.
The uninoculated tube was marked as U, and it showed green color in both aerobic and anaerobic media. This implies that no sugar metabolism has occurred in this tube.
Tube inoculated with Escherichia coli showed yellow color in both anaerobic and aerobic media. The tube was marked as F, and the organism showed a fermentation reaction.
Tube inoculated with Kocuria rosea showed green color in anaerobic medium and yellow color in aerobic medium. The tube was marked as O, and the organism showed oxidation reaction.
Tube inoculated with Alcaligenes faecalis showed green color in anaerobic medium and blue color on the surface of aerobic medium. Tube was marked as N, and the organism showed no carbohydrate metabolism.