The purpose is to see if the microbe can ferment the carbohydrate (sugar) glucose (also known as dextrose) as a carbon source, and to see if the fermentation products include gases.<\/p>\n\n\n\n
When many microbes ferment glucose ( dextrose ) , they produce gases, mainly carbon dioxide and hydrogen. These gases bubble up through the medium and escape into the atmosphere. Tubes of broth media can be made with inverted tubes called Durham tubes which are filled with medium after sterilization. Gas-producing microbes generate enough gas to force the medium from the tube, filling it with bubbles.<\/p>\n\n\n\n
Gas production can also be determined using Triple Sugar Iron Agar (TSIA) slants. When bacteria produce gas from the glucose found in the medium, it forces expansion of the agar and escapes by pushing the agar up in the tube or by creating cracks that separate parts of the agar slant from each other.<\/p>\n\n\n\n
Several media are available for this. Most commonly used is phenol red glucose broth<\/a>. The medium is a nutrient broth to which 0.5-1.0% glucose 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. Additionally, this medium contains a Durham tube , a smaller inverted tube which can serve as a trap for gas bubbles generated during fermentation of sugars.<\/p>\n\n\n\n As mentioned, gas production can also be determined using TSIA slants<\/a>. The medium is inoculated by streaking the slant and stabbing the butt with an inoculating wire (not a loop). After overnight incubation, look for cracks in the agar.<\/p>\n\n\n\n An inoculum from a pure culture is transferred aseptically to a sterile tube of phenol red glucose (dextrose) broth<\/a>. The inoculated tube is incubated at 35-37 C for 24 hours and the results are determined. A positive test consists of a yellow, acidic medium with visible displacement of the gas from the Durham tube.<\/p>\n\n\n\n An inoculum from a pure culture is transferred aseptically to a sterile slant of TSIA<\/a> using a sterile inoculating wire to streak the flat surface of the slant and stab through the slant to inoculate the butt of the tube. After overnight incubation at 35-27 C, appearance of cracks in the agar or movement of the agar above the bottom of the tube indicates gas production.<\/p>\n\n\n\n None.<\/p>\n\n\n\n 1. Select the phenol red glucose 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 only 24 hours. <\/p>\n\n\n\n 6. Retrieve the incubated culture from the incubator.<\/p>\n\n\n\n 7. Observe the color of the culture and the condition of the Durham tube. A positive test is indicated when the tube is yellow and bubbles are present in the Durham tube. Any other result is negative for the generation of gas from glucose. <\/p>\n\n\n\n 8. Record test result<\/a>. <\/p>\n\n\n\n Uninoculated Phenol Red Glucose broth with Durham Tube<\/a><\/p>\n\n\n\n Positive for Glucose Fermentation WITH Gas Production<\/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 (for inoculation of TSIA slants, see the information for that 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