Question

1) What would be the results for Salmonella for the Sulfur reduction test, this identifies sulfur-reducing organisms

a) Black in medium (+) Sulfur reduction (H2S production)

b) no black in the medium (-) Sulfur is not reduced

2) What would the results be for Salmonella for the indole Production test, which has a purpose to test for the activity/ presence of tryptophanase.

a) red in the alcohol layer of Kovac’s reagent would indicate positive results, indicating Tryptophan is broken down into indole and pyruvate.

b) showing the color of the reagent is unchanged would indicate negative results indicating Tryptophan is not broken down into indole and pyruvate.

3) What would the results be for Salmonella for the two step nitrate reduction test, this test for two potential outcomes

1)   Nitrate reductase using a single step reaction of NO3_NO_3^_ à NO2

2) Further reduction via denitrification by other enzymes producing N2, NH3, NH4, NO, and/or N2O (or some other form)

Answer 1

Ans 1-) option (a) is correct.

SIM is the medium on which sulfur reduction test is performed. In this reduction of sullfur occur and it is reduced to hydrogen sulfide.
As hydrogen sulfide is colourless so the SIM medium will use iron as an indicator which combine with hydrogen sulfide in order to form the black coloured complex iron sulfide. Positive test for sulfur reduction test is appearance of black colour in SIM medium.
Salmonella species give positive test as it is a sulfur reducing organism and produces a black colour in the medium and also reduces sulfur to hydrogen sulfide.

Ans2-) option (b) is correct.

Indole production test is the test which is used to identify the organism which has the ability to convert tryptophan into indole by the presence of enzyme tryptophanase and it is confirmed by the addition of kovacs reagent and it reacts with indole to form red coloured complex.
Salmonella gives negative test with indole as after the addition of kovacs reagent there is no colour change.

Ans 3) Option (a) is correct.

Ans 3-) Nitrate reduction test is performed to test the ability of organism to produce the nitrate reductase enzyme which reduces nitrate which are further distinguished on their ability to reduce nitrate into the nitrite or nitrate into nitrogeneous gases. Salmonella test positive with nitrate reduction test and it reduces nitrate into nitrite

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