If the laboratory is not able to identify group-B streptococci (GBS) 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 GBS (Lt), and a group A Streptococcus (GAS) (Rt). 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 “Staph” streak, making sure not to touch the two different organisms (Staph and Strep), but to come close to each other.
The Staph 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 (Lt) near the Staphylococcus streak, but not by the GAS (Rt). This means that the bacterium on the left is GBS because it is producing a CAMP factor.
The test shown towards the bottom of each plate with the two small disks, each labeled “A”, represents a bacitracin-sensitivity test. A positive zone of inhibition around the disk in the right plate, along with a negative CAMP test is a presumptive identification of a group-A streptococcus organism.