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Group B Strep Prevention

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Laboratory Personnel, Slide 5

CAMP Test Comparison

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CAMP Test Comparison
If the laboratory is not able to identify group B streptococci by the Lancefield grouping procedure, there are other microbiologic tests that can be used to identify GBS. This picture shows one of these tests. It is called the CAMP test. CAMP is an acronym for the authors of this test (Christie, Atkinson, Munch, Peterson). The CAMP test takes advantage of the capacity of GBS to produce this CAMP factor; most other hemolytic streptococci do not produce CAMP factor.
This picture shows the growth and CAMP test of a group B Streptococcus (on the left) and a group A Streptococcus (GAS) (on the right). On the top of the agar plate we have inoculated the plate with a Staphylococcus strain (horizontal streak). We then inoculated the GBS (on left) and GAS (on right) perpendicular to the Staphylococcus streak. We inoculated the agar plate so as not to touch the two different organisms (Staphylococcus and Streptococcus) but to come close to each other. The Staphylococcus is used because it produces a lysin that only partially lyses the red blood cells (called beta-lysin). The CAMP factor reacts with the partially lysed area of the blood agar plate to enhance the hemolytic activity. Note the arrowhead shape of the zone of enhanced hemolytic activity by the GBS near the Staphylococcus streak (on left) but not by the GAS (on right). This means that the bacterium on the left is GBS because it is producing a CAMP factor.
The test shown on the bottom of this picture with the two small disks is the bacitracin sensitivity test. A positive zone of inhibition around the disk and a negative CAMP test shown in the agar plate on the right is a presumptive identification of a group A 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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