One test for the identification of group A streptococci is t

One test for the identification of group A streptococci is the latex agglutination test. How does this test identify group A streptococci? What specific antigen(s) of Group A Streptococci do the antibodies of the latex agglutination test bind to? Explain.

Solution

In a latex agglutination test the latex beads coated with antibodies. Majority of pathogenic streptococci possess specific carbohydrate antigens. If the antigen is present, it will react with the antibodies causing the latex beads to clump.One of the Hardy Diagnostics StrepPRO Grouping Kit used for that.In that kit they liberates the specific antigen from the bacterial cell wall using a modified nitrous acid extraction. The extracted antigen, in conjunction with latex agglutination, offers a rapid, sensitive, and specific method for identification of streptococcal groups A, B, C, D, F, and G from primary culture plates. Extraction Reagents 1 and 2 contain a chemical substance able to extract the streptococcal group specific antigens at room temperature. Extraction Reagent 3 contains a neutralizing solution. The neutralized extracts can then be easily identified using blue latex particles sensitized with purified group specific rabbit immunoglobulins. These blue latex particles agglutinate strongly in the presence of homologous antigen and will not agglutinate when homologous antigen is absent.