The purpose is to see if the microbe can use the amino acid lysine as a source of carbon and energy for growth. Use of lysine is accomplished by the enzyme lysine decarboxylase .<\/p>\n\n\n\n
A medium containing lysine and a pH indicator is used. When lysine is used, the pH of the medium rises and the indicator changes color.<\/p>\n\n\n\n
The medium used is lysine decarboxylase broth<\/a>. The medium is a nutrient broth to which 0.5% lysine is added. An important component of the medium is a modest amount of glucose, necessary for the process to proceed. The pH indicator brom cresol purple is purple at neutral or alkaline\/basic pH but turns yellow at pH <5.2.<\/p>\n\n\n\n An inoculum from a pure culture is transferred aseptically to a sterile tube of lysine decarboxylase broth<\/a>. The inoculated tube is incubated at 35-37 C for 24 hours and the preliminary results are determined. The microbe must first use the glucose present to cause the pH to drop. This is indicated by a change from purple to yellow . Once the medium has been acidified, the enzyme lysine decarboxylase is activated. The culture is incubated an additional 24 hours at 35-37 C to allow the microbe to now use the lysine . The final results are then obtained by observing the tube at 48 hours. Change back to purple from yellow indicates a positive test for lysine decarboxylase . Failure to turn yellow at 24 hours or to revert back to purple at 48 hours indicates a negative result.<\/p>\n\n\n\n None.<\/p>\n\n\n\n 1. Select the lysine decarboxylase broth<\/a> medium.<\/p>\n\n\n\n 2. Complete the process of a tube-to-tube aseptic transfer<\/a> to inoculate the medium.<\/p>\n\n\n\n 3. Place the inoculated tube into the 35-37 C incubator. <\/p>\n\n\n\n 4. Press the New Day button<\/a> to move forward 24 hours.<\/p>\n\n\n\n 5. Incubate this test for 24 hours. Make note of the color, then incubate for an additional 24 hours.<\/p>\n\n\n\n 6. Retrieve the incubated culture from the incubator.<\/p>\n\n\n\n 7. Observe test result. If the test protocol was followed as described above, the culture will have changed to yellow due to acids produced in the first 24 hours and then reverted to purple at the 48 hour mark as the amino acid is used. Both color changes must occur for the test to be positive. Any other result is considered negative. <\/p>\n\n\n\n 8. Record your results<\/a>. \u00a0<\/p>\n\n\n\n Uninoculated:<\/a><\/p>\n\n\n\n Positive test MUST have this appearance at 24 hr:<\/a><\/p>\n\n\n\n Positive test MUST NOT have this appearance at 24 hr:<\/a><\/p>\n\n\n\n Positive test MUST have this appearance at 48 hr:<\/a><\/p>\n\n\n\nHow is the test performed? <\/h3>\n\n\n\n
What reagents are added? <\/h3>\n\n\n\n
Performing this test in the VUMIE Online lab<\/h2>\n\n\n\n
Inoculation of Medium<\/h3>\n\n\n\n
Incubation of the Inoculated Medium<\/h3>\n\n\n\n
Determination of Test Results<\/h3>\n\n\n\n