2.8 Immunological techniques for clinical microbiology

Question 1

What do immunological techniques use to give clinical diagnosis

Answer 1

Antibodies

Question 2

Name the immunological techniques covered

Answer 2

Serological testing
Latex Agglutination
Enzyme Linked Immunoassay
Immunochromatographic Methods
Immunoblotting

Question 3

What is serology

Answer 3

The study of antibody-antigen interactions in vitro

Question 4

How is an antibody titre defined?

Answer 4

The highest dilution of serum at which antibody-antigen reaction is observed

Question 5

Describe serological testing

Answer 5

Patien serum is serially diluted and incubated with a known antigen to determine the presence of antibodies against the antigen

Question 6

Describe latex aggulination

Answer 6

Bacterial or Viral Antigens can be attached to
microscopic latex particles.
The antigen coated latex beads are then mixed with
patient antisera on a glass slide
If the antisera contains antibodies which bind to the
antigens this will cause visible clumping of the latex
particles

Question 7

Describe immunochromatographic method

Answer 7

Each sample of bodily fluid is loaded onto a cassette containing chromoatographic media containing coloured antibodies.
Sample migrates along the media.
Pathogen antigens then complex with the labelled antibodies and migrate to the test and control lines. The test line contains an antibody which will form a complex with the labelled anitbody-antigen complex whilst the control line contains antibodies which will form a complex with the labelled anitbodies or the labelled anitbody-antigen complex.

Question 8

What are the stages of an ELISA

Answer 8

1. Each well of the 96 well assay is coated by an anitbody specific to the antigen of interest.
2. The fluid sample is added to each well of the 96 well assay and the antigen binds to the captured antibody
3. Wells are washed with buffer to remove unbound complexes
4. A second specific antibody tagged with an enzyme is added
5. Wells are washed with buffer to remove unbound antibody
6. A substrate is added
7. Intensity of colour is measured in a plate reader