Serogrouping of a Shigella sonnei isolated from a patient stool sample. Results indicate agglutination in group D antisera. (Rebecca Buxton, University of Utah, Salt Lake City, UT)

Serogrouping of a Salmonella species isolated from a patient stool sample.  Results indicate agglutination in polyvalent and group B antisera. (Rebecca Buxton, University of Utah, Salt Lake City, UT)

Lancefield grouping for Streptococcus showing agglutination.  Agglutination is occurring in only one of the six combinations of antigen-antibody used in this test. An unknown species of Streptococcus was subjected to analysis with the Lancefield grouping test, a commercially available latex agglutination immunological assay that detects carbohydrate in the cell wall of streptococci. A standard amount of enzyme-extracted Streptococcus was applied to each of the six rings on the plastic card. A different solution of latex beads coated with a specific Lancefield group antibody was then put into each of the six wells, where presumably only one antibody would recognize the carbohydrate antigen of the unknown Streptococcus. Agglutination occurs when the latex beads coated with antibody specifically bind to the antigen in the ring and crosslinks of multiple latex beads result. Visible agglutination or clumping of the latex beads only occurred in well 4, which corresponds to Lancefield

Lancefield grouping for Streptococcus showing agglutination.  Agglutination is occurring in only one of the six combinations of antigen-antibody used in this test. An unknown species of Streptococcus was subjected to analysis with the Lancefield grouping test, a commercially available latex agglutination immunological assay that detects carbohydrate in the cell wall of streptococci.  A standard amount of enzyme-extracted Streptococcus was applied to each of the six rings on the plastic card. A different solution of latex beads coated with a specific Lancefield group antibody was then put into each of the six wells, where presumably only one antibody would recognize the carbohydrate antigen of the unknown Streptococcus. Agglutination occurs when the latex beads coated with antibody specifically bind to the antigen in the ring and crosslinks of multiple latex beads result. Visible agglutination or clumping of the latex beads only occurred in well 4, which corresponds to

An illustration of the effect of antibody and antigen concentrations on the amount of antibody-antigen precipitate observed in an agglutination reaction. Precipitation occurs when the concentrations of antibody and antigen allow the formation of crosslinked networks, created when antibodies bind two or more antigen epitopes. Maximal precipitate is observed in the concentration range termed "zone of equivalence." In the prozone region, the concentration of antibody exceeds the concentration of antigen and little antibody-antigen precipitation will be formed. In the postzone region, the concentration of antigen exceeds the concentration of antibody, again, limiting the production of antibody-antigen precipitate. (D. Sue Katz, Rogers State University, Claremore, OK)

Positive and negative agglutination. (A) Positive agglutination of Salmonella by anti-Salmonella antibodies.  (B)  No agglutination is observed when anti-Salmonella antibodies are mixed with Escherichia coli. (Anne Hanson, University of Maine, Orono, ME)

Agglutination test.  The color-enhanced latex slide test (Fisher) was used for the detection of the protein–A associated with Staphylococcus aureus.  (A) Staphylococcus aureus showing a positive agglutination reaction indicated by red clumps and a change of background color from purple to blue.  (B) Staphylococcus epidermidis showing a negative agglutination reaction with no clumping and no color change.  Tests were perfomed on cultures incubated on tryptic soy agar for 24 hours at 37^oC. (Tasha Sturm, Cabrillo College, Aptos, CA)

Streptococcal latex agglutination assay testing. The assay shows agglutination indicating a positive reaction for group A Streptococcus (left) and no agglutination indicating a negative reaction for group B Streptococcus (right). (Ken Van Horn, Focus Diagnostics, Inc., Cypress, CA)

Tube agglutination assay.  An unknown organism shows agglutination in the left tube and no agglutination in the right tube. (Ken Van Horn, Focus Diagnostics, Inc., Cypress, CA)

Streptex (Remel) latex agglutination assay for typing of beta-hemolytic streptococci.  The assay shows agglutination indicating a positive reaction for group F streptococci. (Ken Van Horn, Focus Diagnostics, Inc., Cypress, CA)