Question
CAMP reaction
Answer
The CAMP reaction/test (named for its discoverers, Christie, Atkins, and Munch-Petersen) is a rapid presumptive identification test for Group B Streptococcus (Streptococcus agalactiae), exploiting a synergistic haemolytic interaction between the CAMP factor it produces and staphylococcal beta-toxin.
Principle: Group B streptococci produce an extracellular protein called CAMP factor, which enhances (potentiates) the haemolytic activity of staphylococcal beta-haemolysin (sphingomyelinase) produced by Staphylococcus aureus — the two factors act synergistically on red cell membranes.
Procedure: the test organism (suspected S. agalactiae) is streaked at a right angle to, but not touching, a streak of a known beta-haemolysin-producing S. aureus strain on a blood agar plate, and incubated aerobically overnight.
Interpretation: a positive result shows an arrowhead-shaped zone of enhanced (complete) haemolysis at the point where the two streaks approach each other — the shape resembles an arrowhead pointing toward the S. aureus streak, produced by the synergistic action of the two haemolysins where they diffuse and overlap.
Clinical significance: Group B Streptococcus is an important cause of neonatal sepsis and meningitis (acquired from maternal genital colonization during birth) and of postpartum/puerperal infection in the mother; the CAMP test provides a rapid, simple presumptive identification method (alongside other features such as bacitracin resistance and hydrolysis of hippurate) in routine clinical microbiology laboratories.