Carbohydrate utilization Sucrose fermentation in purple broth test medium. Bromcresol purple is the pH indicator. Introduction - Microorganisms can potentially use a variety of substances for energy, including carbohydrates. Bacteria can be differentiated by the carbohydrates they utilize and the types and quantities of acids produced if they are fermenters. In bacteriological test systems, this process is detected by observing color changes in pH indicators as acid products are formed.
Some organisms also produce gas, carbon dioxide and hydrogen, as byproducts of fermentation.
The gas results through the cleavage of formic acid and any bacterium that forms gas in carbohydrate test medium must first form acid. Strict aerobes usually utilize carbohydrates without the release of acids therefore detection is not by pH change but by the ability of the organism to use the substrate as the sole carbon source. Media and Reagents - Carbohydrate test medium is used for fermentation reactions. The base medium consists of a buffered peptone solution containing a pH indicator. The medium can be solidified with agar, however ambient oxygen concentration may suppress some fermentation reactions.