Bacteria are identified based largely on what organic compounds they can break down. The range of compounds used depends on the collection of enzymes a species of bacteria can make. Galactose is a sugar that some bacteria can use because of an enzyme that begins the breakdown of this compound. Phenol red galactose broth is thus used to determine whether the microbe can use the sugar galactose for carbon and energy.<\/p>\n\n\n\n
If galactose can be used, the microbe will accumulate acidic byproducts. In a positive test, the pH indicator in the medium changes color from its normal red to yellow, indicating acid production.<\/p>\n\n\n\n
The medium is a nutrient broth to which 0.5-1.0% galactose is added. The pH indicator phenol red is red at neutral pH but turns yellow at pH <6.8. It also changes to magenta or hot pink at pH >8.4.<\/p>\n\n\n\n
For information on how to determine the ability of a microbe to use galactose, refer to the galactose fermentation test<\/a>.<\/p>\n\n\n\n
\n\n\n\nVUMIE is the flight simulator of microbiology labs.<\/h2>\n\n\n\n