16.5: Procedure for Direct Serologic Testing

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A. Serologic Typing of Shigella

1. Using a wax marker, draw two circles (about the size of a nickel) on each of two clean glass slides . Label the circles A, B, C, and D.

2. Add one drop of the suspected Shigella (unknown antigen) to each circle. (The Shigella has been treated with formalin to make it noninfectious but still antigenic.)

3. Now add one drop of known Shigella subgroup A antiserum to the "A" circle, one drop of known Shigella subgroup B antiserum to the "B" circle, one drop of known Shigella subgroup C antiserum to the "C" circle, and one drop of known Shigella subgroup D antiserum to the "D" circle.

4. Rotate the slide carefully for 30-60 seconds.

Agglutination of the bacteria, indicates a positive reaction.

No agglutination is negative.

5. Dispose of all pipettes and slides in the disinfectant container.

B. Serologic Typing of Streptococci: The Clearview® Strep A Exact II Dipstick Test

1. Add 4 drops of Extraction Reagent #1 to the extraction tube. This reagent contains 2M sodium nitrite and should be pink to purple in color.

2. Add 4 drops of Extraction Reagent #2 to the extraction tube. This reagent contains 0.3M acetic acid. The solution must turn yellow in color.

3. Place the throat swab in the extraction tube and roll it with a circular motion inside the tube. Let stand for at least 1 minute.

4. Squeeze the swab firmly against the extraction tube to expel as much liquid as possible from the swab and discard the swab in the biowaste container.

5. Immerse the test strip into the extraction tube with the arrows pointing toward the extracted sample solution. Leave the strip in the tube and start timing.

6. Read results in 5 minutes. A red band in the control region and a red band in the test region indicates a positive test. A single red band in the control region only indicates a negative test. No colored band in the control region indicates an invalid test.

C. Serologic Testing to Detect Pregnancy: The Alere hCG-Dipstick®

1. Dip the hCG dipstick into the urine up to the maximum line on the strip for 5 seconds.

2. Place the test dipstick on a flat, non-absorbant surface and read the results at 3-4 minutes. Do not interpret after the appropriate read time.

3. If hCG is present in the urine at a concentration of 25mlU/ml or greater, a positive test, a pink-to-red Test line will appear along with a red Control line in the Result Window. If hCG is absent or present at very low levels, a negative test, only a red Control line appears in the Result Window.

D. The Direct Fluorescent Antibody Technique

Observe the demonstration of a positive direct fluorescent antibody test for Neisseria gonorrhoeae .

Contributors and Attributions

Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)