Fermentative organisms utilize the carbohydrate in both the open and sealed tubes and the colour of the medium changes from green to yellow. Oxidative organisms, however, are able to use the carbohydrate only in the open tube. There is no carbohydrate utilization in the sealed tube (medium remains green).
Although most genera of aerobic bacteria are either carbohydrate oxidizers or fermenters, the production of acid may be slow and therefore cultures are usually incubated for 7-14 days.
Oxidation fermentation (O-F) medium Glucose, maltose, and sucrose O-F media are the most commonly used.
Sterile paraffin oil (liquid paraffin)
Using a sterile straight wire, inoculate the test organism to the bottom of two bottles (or more if testing several carbohydrates) of sterile O-F medium. Use a heavy inoculum.
Cover the incculated medium in one of the tubes (or one from each carbohydrate pair) with a 10mm deep layer of sterile paraffin oil or molten wax.
Incubate the tubes at 35-37OC for up to 14 days. Examine daily for carbohydrate utilization as shown by acid production.