| Section: Microbiology Methods » Diagnostic Microbiology In Action
Simple Carbohydrate Fermentations
Media for testing carbohydrate fermentation are often prepared as tubed broths, each tube containing a small inverted “fermentation” (or Durham) tube for trapping any gas formed when the broth is inoculated and incubated (see colorplate 18). Each broth contains essential nutrients, a specific carbohydrate, and a color reagent to indicate a change in pH if acid is produced in the culture (the broth is adjusted to a neutral pH when prepared). Organisms that grow in the broth but do not ferment the carbohydrate produce no change in the color of the medium, and no gas is formed. Some organisms may produce acid products in fermenting the sugar, but no gas, whereas others may form both acid and gas. In some cases, organisms that do not ferment the carbohydrate use the protein nutrients in the broth, thereby producing alkaline end products, a result that is also evidenced by a change in indicator color (see colorplate 19).
Record your results in the following table. Use these symbols to indicate specific changes observed in the broths.
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