Purpose

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

 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 proximity.

Method

1. Streak a beta-lysin–producing strain of S. aureus down the center of a sheep blood agar plate.

 2. Streak test organisms across the plate perpendicular to the S. aureus streak within 2 mm. (Multiple organisms can be tested on a single plate).

3. Incubate overnight at 35°-37°C in ambient air.

Expected Results

Positive: Enhanced hemolysis is indicated by an arrowhead-shaped zone of beta hemolysis at the juncture of the two organisms (Figure 1, A).

Negative: No enhancement of hemolysis (Figure 1, B).

Limitations

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.

Quality Control

 Positive: Streptococcus agalactiae (ATCC13813)—enhanced arrowhead hemolysis Negative: Streptococcus pyogenes (ATCC19615)—beta-hemolysis without enhanced arrowhead formation

Fig1. CAMP test. A, Positive; arrowhead zone of beta-hemolysis (at arrow), typical of group B streptococci. B, Negative; no enhancement of hemolysis.