Question

Test or Medium Purpose API System Enterotube Citrate Glucose H2S Indole Lysine decarboxylase Omithine decarboxylase Urease T T T Arial 3 (12pt) T-. E < 1 * Words 0

Answer 1

Answer 1:

1. Citrate

• Purpose - Sodium citrate and Dihydrogen ammonium phosphate are used as sole source of carbon and nitrogen respectively. The ability of the organism is checked to use these inorganic salts as source as carbon and nitrogen respectively. Change in pH to alkaline is noted by change in color of the medium from green to blue.
  
• API system -  The test is present in the 5th well of the API20E. While inoculating, this well needs to be filled up to the brim.
  
• Enterotube - The test is present in the 12th tube of the Enterotube.

2. Glucose

• Purpose - The ability of the organism to ferment glucose as source of carbon and energy. Phenol red indicator indicates change in pH to acidic when glucose is fermented and mixed acids are produced. Inverted durhams' tube is placed in the broth tube before sterilization. The production of gas from glucose is indicated by a bubble trapped and visible in the inverted tube.
  
• API system - The test is present in the 12th well of the API20E
  
• Enterotube - The test is present in the 1st tube of the Enterotube. The fermentation is allowed in anaerobic conditions and solid medium, cracks up to indicate the presence of gas. The indicator used in this medium is Cresol red instead of Phenol red.

3. H₂S

• Purpose -It is used to check the ability of an organism to produce Hydrogen sulphide (H₂S). The media contains Thiosulphate and iron(peptonized) as indicators for this reaction. When H₂S is produced, it reacts with iron producing ferrous sulphide precipitation which is black in color. Appearance of the black color indicates a positive test.
  
• API system -The test is present in the 6th well of the API20E
  
• Enterotube - The test is present in the 4th tube of the Enterotube, combined with Indole. The medium contains Thiosulphate, ferric ammonium citrate (as source of iron) along with tryptophan (for indole)

4. Indole

• Purpose - The ability of the organism to degrade tryptophan using enzyme tryptophanase is tested. Tryptone water is used as the base medium rich in tryptophan. When tryptophan is brokendown, it produces indole and Kovac's reagent is added after incubation to check for presence of this compound. A pink colored ring on top of the broth shows a positive test.
  
• API system - The test is present in the 9th well of the API20E.
  
• Enterotube - The test is present in the 4th tube of the Enterotube, combined with H₂S.

5. Lysine decarboxylase

• Purpose - It is used to identify ability of the organism to produce decarboxylase enzyme for amino acid lysine. The medium usually contains dextrose sugar, initially used the organism to produce acids that change the color of the medium. The indicator bromocresol purple turns yellow in acidic conditions. If the organism produces enzyme for decarboxylation of Lysine, it will produce alkaline end products which will turn back the medium from yellow to purple This indicates positive reaction.
  
• API system - The test is present in the 3rd well of the API20E. It is labeled as LDC. After inoculating, the well, the top of the well is layered with paraffin oil to provide anaerobic conditions.
  
• Enterotube - The test is present in the 2nd tube of the Enterotube. The medium is covered with wax to create anaerobic conditions.

6. Ornithine decarboxylase

• Purpose - It is used to identify ability of the organism to produce decarboxylase enzyme for amino acid ornithine. The medium usually contains dextrose sugar, initially used the organism to produce acids that change the color of the medium. The indicator bromocresol purple turns yellow in acidic conditions. If the organism produces enzyme for decarboxylation of ornithine, it will produce alkaline end products which will turn back the medium from yellow to purple This indicates positive reaction.
  
• API system - The test is present in the 4th well of the API20E. It is labeled as ODC. After inoculating, the well, the top of the well is layered with paraffin oil to provide anaerobic conditions.
  
• Enterotube - The test is present in the 3rd tube of the Enterotube. The medium is covered with wax to create anaerobic conditions.

7. Urease

• Purpose - The test is used to identify the ability of certain organisms to use urea as a sole source of Carbon and energy. They produce enzyme urease which breakdown urea. Indicator Phenol red is added to the medium. When organisms breakdown urea, they release ammonia which increases the pH of the medium and the indicator gives a distinct pink colour on alkaline pH.
  
• API system -The test is present in the 7th well of the API20E.
  
• Enterotube - The test is present in the 11th tube of the Enterotube

Answer 2:

The commonly used carbohydrates tested to determine fermentation ability of bacterial species are:

1. Glucose
2. Lactose
3. Sucrose
4. Mannitol