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CAMP Test- Principle, Procedure and Result Interpretation
Objective of CAMP Test
The Christie, Atkins, and Munch-Peterson (CAMP) test is used to differentiate group B streptococci (Streptococcus agalactiae–positive) from other streptococcal species. Listeria monocytogenes also produces a positive CAMP reaction.
Principle of CAMP Test
Certain organisms (including group B streptococci) produce a diffusible extracellular hemolytic protein (CAMP factor) that acts synergistically with the beta-lysin of Staphylococcus aureus to cause enhanced lysis of red blood cells. The group B streptococci are streaked perpendicular to a streak of S. aureus on sheep blood agar. A positive reaction appears as an arrowhead zone of hemolysis adjacent to the place where the two streak lines come into
Procedure of CAMP Test
- Streak a beta-lysin–producing strain of S. aureus down the center of a sheep blood agar plate.
- Streak test organisms across the plate perpendicular to the S. aureus streak within 2 mm. (Multiple organisms can be tested on a single plate).
- Incubate overnight at 35°-37°C in ambient air.
Result Interpretation of CAMP Test
Positive: Enhanced hemolysis is indicated by an arrowhead-shaped zone of betahemolysis at the juncture of the two
Negative: No enhancement of hemolysis.
Limitations of CAMP Test
A small percentage of group A streptococci may have a positive CAMP reaction. The test should be limited to colonies with the characteristic group B streptococci morphology and narrow zone beta-hemolysis on sheep blood agar.
Positive: Streptococcus agalactiae (ATCC13813)—enhanced arrowhead hemolysis
Negative: Streptococcus pyogenes (ATCC19615)—beta-hemolysis without enhanced arrowhead formation