PHYSIOLOGICAL TESTS Interpret results for these tests and identify colors for po
ID: 278877 • Letter: P
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PHYSIOLOGICAL TESTS Interpret results for these tests and identify colors for positive or negative results Name the reagents required to complete the results for O Nitrate reduction & Nitrite formation O Starch hydrolysis O Casein hydrolysis O Gelatin hydrolysis O Citrate utilization Carbohydrate fermentation, acid/gas formation O Methyl Red test & Voges Proskaeur (MR-VP) D Tryptophan Hydrolysis and Indole formation Environmental & Industrial Microbiology: Water Analysis Analysis and bacteriological safety test for water test Recall steps, culture media, and results for presumptive and confirmed tests Recall how yogurt is made What tests are the following used for? O Kovac's Reagent O EMB O Sulfanilic acid (Reagent A) O Barritt's Reagent A & B 0 Ice & Refrigeration 0 Nigrosin O Alpha-Naphythyl amine (Reagent Zinc powder O Coplin jar O Malachite green O Carbol Fuchsin Safranin Acid-alcohol Turbidity Methylene Blue O Crystal violet D lodine O Zone of inhibitionExplanation / Answer
1. Carbohydrate fermentation test- to test whether a particular carbohydrates can be fermented by a bacteria or not. Phenol red is generally used pH indicator for the test. A change in color from red to yellow of the medium shows fermentation occurred and no change in color shows no fermentation. Gas production is shown by a gas bubble in Durham tube.
2. Methyl red test is performed to check whether a microbe can fermentation the mix acid when glucose is supplied. This test is used to differentiate beteeen various enteric bacteria. Methyl red which is the pH indicator for the test remains red at pH 4.4 and converts to yellow at pH above 5.1, thus onky when large amount of acid is produced the color changes. Test is positive when the medium turns red and is negative when remains yellow.
Voges Proskaeur test - Pyruvic acid upon metabolization by enzymes present in various microbes result in formation of acetion. This product in presence of atmospheric oxygen and 40% potassium hydroxide gives a red color compund namely diacetyl which shows the positive results of the test.
3. Tryptophan hydrolysis and indole formation - this test is performed to check whether am organism can convert amino acid tryptophan into indole or not. The formation of indole is detected by Kovac’s or Ehrlich’s reagent which reacts with indole to produce a red coloured compound. Thus test is used to differentiate Enterobacteriaceae and other genera.
4. Nitrate reduction test - this test is used for differentiation of members of Enterobacteriaceae on the basis of the fact whether they can produce nitrate reductase enzyme or not which can hydrolyze nitrate to nitrite.
If the organism can convert nitrate to nitrite, the nitrites can form nitrous acid which upon addition of sulfanilic acid produces diazotised sulfanilic acid. This acid upon reaction with alpha naphthylamine firms a red colored compound.
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