What is this medium used for? The pathways used to metabolize a sugar under aerobic conditions differ from those used under anaerobic conditions. When oxygen is present, the process is called oxidation, and when oxygen is absent it is called fermentation. This test provides insight into the ability of the bacterium to use glucose by both methods (OF = oxidation, fermentation). Two tubes of OF glucose medium are used, one of which has a covering layer of sterile mineral oil as an oxygen barrier.
How is the oxidation of glucose determined? If glucose is metabolized in the tube without the oil overlay, the microbe can oxidize glucose. This is made obvious by the change in color of a pH indicator from the normal green of the medium to yellow due to the acids present. Because all bacteria included in this edition of VirtualUnknown™ Microbiology are able to oxidize glucose, this portion of the test is not performed.
How is the fermentation of glucose determined? If glucose is metabolized in the tube with oil overlay, the microbe can ferment glucose. This is made obvious by the change in color of a pH indicator from the normal green of the medium to yellow due to the acids present.
What is the content of the medium? OF glucose, with or without oil overlay, consists of a nutrient medium to which 1% glucose has been added. The pH indicator is brom thymol blue, which is green at neutral pH and turns yellow at pH <6.0. It gets its name because it turns blue at pH >7.6. The oil overlay is sterile mineral oil that is added to the medium either before or after sterilization.
How are these tests performed? For information on how to detect oxidation and fermentation of glucose using OF glucose medium, refer to the OF Glucose test.