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Group B Strep Prevention

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Slides of Agglutination Commercial Tests

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Slides of Agglutination Commercial Tests
The most accurate way to identify a group B Streptococcus is to demonstrate that the bacteria in question has the Lancefield group B antigen on the surface of the bacteria. The Lancefield antigens are called group A, B, C, D, etc. Each of the antigens is associated with a certain kind of bacteria. In the case of GBS, the antigen we are looking for is called group B. This picture shows a slide agglutination test that is used to identify the group antigens of streptococci. There are two different commercial products shown in this picture, the top two circles are one test and the bottom two circles are another test. The general procedure, for this test, is to make a small suspension of bacteria from the blood agar plate with a bacteriologic loop of culture and place it on the test card shown above. The suspension is placed in both circles. Group specific antibodies from the commercial grouping kit are then placed on the suspension. Next, the suspension of bacteria is mixed with the group specific antibody and tilted back and forth for about one minute. In this case, we put group B antibodies in the circles on the left and group A antibodies in the circles on the right. A positive agglutination reactions are shown on the left (both commercial tests). Note the clumping of the suspension of bacteria. A negative reaction is shown on the right. The suspensions mixed with the group A reagent are smooth; no clumps are apparent. These results indicate we have identified a group B Streptococcus.
Page Last Modified: April 20, 2008
Content Last Reviewed: April 20, 2008
Content Source: National Center for Immunization and Respiratory Diseases
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