CAMP Test: Principle, Procedure, Result and Interpretation

CAMP test

CAMP Test  to identify presumptively S. agalactiae

The CAMP test uses to identify preemptively Streptococcus agalactiae. It was first described in 1944 by Christie, Atkins, and Munch-Petersen, and the CAMP test is an acronym of their names.

Principle of CAMP Test

The beta lysin produced by Staphylococcus aureus is sphingomyelinase in nature, which acts on the sphingomyelin present on the cell membrane of sheep red blood cells. This results in the formation of ceramide which is cleared by the action of CAMP factor I.e. extracellular diffusible protein secreted by S. agalactiae thus producing enhanced hemolysis.

Requirements for CAMP Test

  • 5-10% sheep blood agar plate
  • Test organism
  • Staphylococcus aureus ATCC 25923
  • Inoculating loop
  • Bunsen burner
  • Quality control strains
  • BOD Incubator

Quality control

1. Positive control: Streptococcus agalactiae ATCC 13813

2. Negative control: Streptococcus pyogenes ATCC 19615

Procedure of CAMP Test

Perform the test by streaking a known beta hemolytic Staphylococcus aureus strain across a 5-10% sheep blood agar plate and then inoculate the test organism at right angles to it (3-4 cm long streak). The test organism i.e. S. agalactiae must not touch the inoculum. Inoculate control strains S. pyogenes and S. agalactiae on the same plate as negative and positive controls respectively as performed in the test.  Incubate the plate at 35-37oC in ambient air overnight.

Results and interpretations of  CAMP Test

An arrowhead-shaped area of hemolysis appears due to contact of ceramide and CAMP factors produced by S. agalactiae denotes positive

Lacking an arrowhead of hemolysis: Negative

Negative Control: no arrowhead of hemolysis

Positive control: the presence of an arrowhead of hemolysis

Note: From the above picture, NC and PC are missing and only tests were run. All are showing an arrowhead of hemolysis, therefore the test organism is positive.

Keynotes 

Beta-hemolytic streptococcus can be identified presumptively S. agalactiae (group B) due to having the following features-

Bacitracin: Resistant

Co-trimoxazole: Resistant

CAMP test: Positive

Few groups A streptococci may be CAMP test positive if you incubate the test plate in a candle jar, or in a CO2 atmosphere, or under anaerobic conditions. Therefore, ambient air incubation is necessary.

Bibliography

  1. Clinical Microbiology Procedure Handbook- Second  Edition update -Lynne S. Garcia
  2. Biochemical Tests for Identification of Medical Bacteria- The Williams & Wilkins Company Baltimore -Jean F. MacFaddin
  3. District Laboratory Practice in Tropical Countries-Monica Cheesbrough

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