WIDAL TEST

WIDAL TEST

(QUALITATIVE SLIDE AGGLUTINATION METHOD)

 

Aim

            To diagnose enteric fever caused by Salmonella species using qualitative slide agglutination test.

 

Principle

 

            The Widal test is applied for the diagnosis of enteric fever that includes typhoid and paratyphoid caused by Salmonella typhi and Salmonella paratyphi respectively. For the slide agglutination test, stained Salmonella antigens are used to detect the presence of specific agglutinin in the patient’s serum. The slide agglutination test is used as a primary screening procedure. There are some agglutinins that are produced in the patient’s serum during the fever period, which react with somatic antigen O of Salmonella typhi, A or B of Salmonella paratyphi and then with flagellar antigen H which is common in most of the Salmonella species. In this test four specific antigen suspensions are used viz H, Salmonella typhi (O antigen), Salmonella paratyphi - A and Salmonella paratyphi - B. If agglutination occurs in ‘O’ antigen added circle, then it is considered positive for Salmonella typhi. If agglutination occurs in A or B antigen added circle, then it is confirmed as positive for paratyphoid. Agglutination will occur in H antigen circle for all the cases of antigens like O, A, and B.

 

Materials required

1.      Widal test kit

2.      Widal test slide

3.      Suspected serum sample

4.      Pipette

5.      Applicator stick

 

Procedure

1.      A clean glass marked with six circles was taken.

2.      The circles were labeled as “H”, “O”, “A”, “B”, positive control and negative control from the first circle to the last.

3.      One drop of undiluted serum was placed in the first four circles with the help of a sterile pasture pipette.

4.      One drop of postive control serum and one drop of negative control serum was placed in the fifth and the last circle respectively.

5.      One drop of H antigen was added to the first circle and one drop of Salmonella typhi O antigen was added in the second circle. Salmonella paratyphi A antigen and Salmonella paratyphi B antigen were added in the third and fourth circles respectively.

6.      One drop of ‘H’ antigen was placed at the fifth circle and sixth circle.

7.      With separate applicator sticks serum and the antigen was mixed together and was spread well to fill the whole of the individual circle. Then slide was observed for agglutination.

Result:

The given test patient’s serum is positive for typhoid.

The given test patient’s serum is positive for paratyphoid A or B

The given test patient’s serum is negative for typhoid and paratyphoid.

 

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(Draw and write in the left side of your observation note book)

Observation:

 

DRAW THE SLIDE PICTURE HERE

 

The agglutination has (occurred / not occurred) in H antigen circle.

The agglutination has (occurred / not occurred) in O antigen circle.

The agglutination has (occurred / not occurred) in A antigen circle.

The agglutination has (occurred / not occurred) in B antigen circle.