Presentation on theme: "Ex. 18: IMViC Reactions Objectives ?? Indole production test Methyl red test Voges-Proskauer test Citrate utilization test."— Presentation transcript:
Ex. 18: IMViC Reactions Objectives ?? Indole production test Methyl red test Voges-Proskauer test Citrate utilization test.
Materials needed per team of two students: 2 tryptone broth tubes 2 MR-VP broth tubes 2 Simmons citrate slants Pure cultures needed per table: Escherichia coli Enterobacter aerogenes Work as a team of two. Each team member will work with one bacterial species Day 1
Materials needed per team of two: 2 clean tubes and two 1 ml transfer pipettes Materials needed per table: Small biohazard bag Kovac’s reagent Methyl red indicator reagent VP reagents A and B Work as a team of two. Each team member will work with one bacterial species Day 2
Indole Test Checks for Tryptophanase Medium: 1% Tryptone broth Test for indole with Kovac’s reagent DMABA in Kovac’s reagent combines with indole and forms red band at the top of the medium
Table 18-1: Indole Production Results and Interpretation ResultInterpretationSymbol Red in the alcohol layer of Kovac’s reagent Tryptophan is broken down into indole and pyruvate + Reagent color is unchanged Tryptophan is not broken down into indole and pyruvate Enterobacter aerogenes E. coli
Methyl Red and Voges-Proskauer Tests Physiologically related tests, use same medium (MRVP broth), NB with glucose MR test checks for large amounts of acid endproducts from glucose fermentation methyl red phenol redDo not confuse methyl red indicator with phenol red indicator!!! VP test checks for production of acetoin, a neutral fermentation end product
Table 18-2: Methyl Red Test Results and Interpretation ResultInterpretationSymbol RedMixed acid fermentation+ No color changeNo mixed acid fermentation Table 18-3: Voges-Proskauer Test Results and Interpretation ResultInterpretationSymbol RedAcetoin produced+ No color changeAcetoin is not produced
MRVP after incubation and before adding test reagents
MR test After addition of 3 -4 drops of methyl red indicator Explain the meaning of this outcome
VP Test After addition of 15 drops of VP reagent A, and 5 drops of VP reagent B Explain the meaning of this outcome E. a.E. c.
Citrate Utilization Test Checks if organism has citrate permease Simmons citrate agar also contains ammonium phosphate as sole N-source and bromothymol blue as indicator. If bacterium is able to use citrate it will also convert ammonium phosphate to NH 3 and NH 4 OH
Table 18-4: Citrate Test Results and Interpretation ResultInterpretationSymbol Blue (even a small amount) Citrate is utilized+ No growth or weak growth with no color change Citrate is NOT utilized
Could an organism be both MR and VP positive? Explain.