Exercise 56: Slide Agglutination Test for S. aureus

What types of compounds in bacterial cells can serve as antigens?

Proteins, polysaccharides, lipids and nucleic acids.

What is the importance of doing controls?

Controls allow the comparison of an experimental result to a fully agglutinated result (positive control) and a non-agglutinated result (negative control).

Protein A & Coagulase

-Important virulence factors for S. aureus -Coagulase causes clot formation in capillaries at infection sites, thus preventing leukocytes from reaching the area of infection. -Protein A is a cell wall component of S. aureus that reacts with antibody molecules and coats the surface of the bacterial cell with host immunoglobulins, and protects the bacterial cell by inhibiting phagocytosis by WBCs and destruction of the bacterial cell

Equivalence Point

-Precise ratio of antibody to antigen occurs and causes a visible precipitate reaction

Agglutination Test

-Soluble antigens such as proteins can be detected using a modified procedure (agglutination) where antibodies that have been produced against soluble antigens are absorbed, or chemically linked, to polystyrene latex particles -Polystyrene particles act as carriers of the antibodies, and when they react with their soluble antigen an agglutination reaction occurs between the antibodies carried on the polystyrene particles and the antigen.

What are immunoglobulins?

Antibodies

Positive Test for Coagulase and/or Protein A

Antigens will react with the latex particles and antibodies to cause agglutination of the latex spheres

What two S. aureus antigens are being detected with the use of this test kit?

Coagulase & Protein A

Negative Test for Coagulase and/or Protein A

No agglutination means that the test organism does not produce the virulence factors

What is the advantage of the latex test as compared to the ordinary precipitin-like reaction?

Results occur more rapidly and are much easier to visualize than ordinary precipitin-like reactions that demonstrate the presence of soluble antigen.

What definitive test for S. aureus is highly correlated with this agglutination test?

S. aureus is the only staphylococcal species positive for the coagulase tube test, which is demonstrated by the clotting of plasma. There is 97% correlation with the agglutination test.

What is a serotype of an organism?

Serotypes are more specific than species. A serotype is a group of bacteria possessing a common set of antigens.

What advantages does the agglutination test have over the definitive S. aureus test?

The agglutination test is more rapid and also tests for a second antigen of S. aureus (protein A).

What is agglutination?

The formation of visible clumps which appear when antibodies react with the antigens present on a bacterial cell.

What types of controls are used for the slide agglutination?

The negative control is a mixture of antigen and saline (antibody is missing) and so will not agglutinate. The positive control contains both antibodies and antigens and will agglutinate.