OF (Oxidation Fermentation) media are used for the determination of oxidative and fermentative metabolism of carbohydrates by gram-negative rods on the basis of acid reaction in either the open or closed system.

• High concentration of added carbohydrates
• Dipotassium phosphate adds buffering capacity
• Agar permits the determination of motility
• Dextrose provides a source of carbohydrates

Changes in the cover agar are considered to be due to true fermentation, while changes in the open tubes are due to oxidative utilization of the carbohydrate present. If the carbohydrate is not utilized by either method, there is no acid production in either tube.