CAMP test: Principle, procedure, Result and Interpretation

CAMP test

CAMP test  to identify preemptively S. agalactiae

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

Principle

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

5-10% sheep blood agar plate

Test organism

Staphylococcus aureus ATCC 25923

Inoculating loop

Bunsen burner

Quality control strains

Quality control

1. Positive control: Streptococcus agalactiae ATCC 13813

2. Negative control: Streptococcus pyogenes ATCC 19615

Procedure

1. 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).

2. The test organism i.e. S. agalactiae must not touch the inoculum.

3. Inoculate control strains S. pyogenes and S. agalactiae on same plate as negative and positive controls respectively as performed in test.

4. Incubate the plate at 35-37oC in ambient air for overnight.

Results and interpretations

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

Lacking an arrow head of hemolysis: Negative

Negative Control: no arrow head of hemolysis

Positive control: presence of an arrow head of hemolysis

Note: From above picture, NC and PC are missing and only tests were run.

All are showing an arrow head of hemolysis, therefore test organism is positive.

Key notes

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

Bacitracin: Resistant

Co-trimoxazole: Resistant

CAMP test: Positive

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

Bibliography

  • Clinical Microbiology Procedure Handbook- Second  Edition update

-Lynne S. Garcia

  • Biochemical tests for Identification of medical Bacteria- The Williams & Wilkins Company Baltimore

-Jean F. MacFaddin

  • District Laboratory Practice in Tropical Countries

-Monica Cheesbrough

  • A hand book of Clinical Microbiology

By Prof. Dr. Bharat Mani Pokhrel

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