CAMP Test- Presumptive Identification of Group B Streptococcus (S. agalactiae)

CAMP test was named after its authors Christie, Atkinson, Munch, Peterson in 1944. This test is used to detect the CAMP factor produced by Group B Streptococcus (Streptococcus agalactiae). GBS is the only beta-hemolytic Streptococcus which yields a positive CAMP test.

CAMP factor is a diffusible, heat-stable, extracellular protein produced by Group B Streptococcus that enhances the hemolysis of sheep erythrocytes by Staphylococcus aureus. It acts synergistically with the beta hemolysin produced by S. aureus to induce enhanced hemolysis of sheep or bovine RBCs but not human, rabbit or horse RBCs.

Procedure and Interpretation: 

A known hemolytic strain of S. aureus (ATCC 25923) is streaked in a straight line across the centre of the sheep blood agar plate. Test inoculum is streaked in a straight line (2-3 cms in length) perpendicular to S.aureus streak but without touching it. A known Group B Streptococcus may also be streaked similarly as a positive control. Four-five test organisms may be tested per plate. The plate is incubated at 37oC for 18-24 hours.

A positive test for CAMP factor appears as “arrowhead” hemolysis between the junction of growth of S.aureus and Group B Streptococcus.

Other Uses of CAMP Test:
1. A similar test has been described for Listeria ivanovii, where an “arrowhead” hemolysis occurs appear between streaks of Listeria ivanovii and Rhodococcus equi. 
2. Reverse CAMP test can be used for differentiation of Clostridium perfringens from other Clostridium species. Here, a CAMP positive Group B Streptococcus is streaked in the center of sheep blood agar, and Clostridium perfringens is streaked perpendicular to it. Following incubation at 37oC for 24-48 hours in anaerobic conditions, an “arrowhead” hemolysis is seen between growth of C. perfringens and Group B Streptococcus. This is because of alpha toxin produced by C. perfringens interacts with CAMP factor and produce synergistic hemolysis.