CAMP Test: Principle, Procedure, Results

By Acharya Tankeshwar •  Updated: 05/09/22 •  5 min read

CAMP test is used for the presumptive identification of Group B beta-hemolytic streptococci, Streptococcus agalactiae.

CAMP test is effective for the “prompt and reliable” identification of Streptococcus agalactiae in the clinical lab, as results could be observed in as little as 18 hours and require few manipulations. CAMP test rarely gives false positives with other Streptococcus. This hemolytic phenomenon was first described in 1944 by Christie, Atkins, and Munch-Petersen, and CAMP test is an acronym for their names.

Principle

The hemolytic activity of the beta-hemolysin produced by most strains of Staphylococcus aureus is enhanced by an extracellular protein produced by group B streptococci. Interaction of the beta-hemolysin with this factor causes “synergistic hemolysis,” which is easily observed on a blood agar plate. This phenomenon is seen with both hemolytic and non-hemolytic isolates of group B streptococci.

CAMP Test
CAMP Test Positive (arrowhead increased zone of hemolysis)

Quality control

Test each lot of beta-lysin reagent or disks with a positive and negative control by streaking them in a line parallel to the test organism.

Organisms

  1. S. agalactiae ATCC 12386-CAMP test positive
  2. Streptococcus pyogenes ATCC 19615-CAMP test negative
  3. Periodically use an in-house laboratory strain of Arcanobacterium haemolyticum to demonstrate the reverse CAMP test for training purposes.

Procedure for CAMP test

Standard Method

  1. Down the center of a blood agar plate, make a single straight line streak of beta-hemolysin producing Staphylococcus aureus
  2. Taking care not to intersect the staphylococcal streak, inoculate a streak of the test organism (beta-hemolytic streptococci to be identified) perpendicular to the staphylococcal streak. Make these streaks in such a way that, after incubation, the growth of the two organisms will not be touching.
  3. The streptococcal streak should be 3 to 4 cm long.
  4. Inoculate known group A and B streptococcal strains similarly on the same plate as negative and positive controls respectively.
  5. Label the location of each streak on the back of the plate.
  6. Incubate the plate at 35°C in ambient air for 18-24 hours.

Disk method

  1. Place disks containing beta-lysin of S.aureus on a warmed blood agar plate.
  2. Streak microorganisms 2 to 3 mm from the edge of the disk.
  3. Incubate the plate overnight at 35°C in a CO2 incubator.

Spot rapid method

  1. Place 1 drop or a 10 μl loopful of CAMP liquid reagent next to a presumptive S. agalactiae colony growing on a blood agar plate. Do not worry if the liquid touches or even engulfs the colony.
  2. Incubate the plate right side up, to prevent the spot CAMP reagent from running over the plate’s surface, for 20 min at 35°C.
  3. Examine with transmitted light for a zone of enhanced hemolysis next to the colony.
  4. Reincubate for up to 30 min if the reaction is initially negative. Use a hand lens if necessary for examining the plate.
  5. Refrigeration may enhance reaction after incubation.
CAMP Test
CAMP test :
A. Streptococcus agalactiae (positive)
B. Streptococcus pyogenes (Negative)
Image Source: ASM

Results and Interpretations

Limitation of CAMP test

  1. Some group A streptococci will be CAMP test positive if the test plate is incubated in a candle jar, in a CO2  atmosphere, or under anaerobic conditions. Therefore, ambient air incubation should be used.
  2. S. pyogenes can give a reaction that may be interpreted as positive. When there is confusion check for
    pyrrolidonyl-β-naphthylamide (PYR) test. S. pyogenes is PYR positive whereas S. agalactiae is PYR negative.
  3. CAMP test has a 98% sensitivity for detecting S. agalactiae so isolates with a negative CAMP test could still be S. agalactiae and may require further testing.
  4. If the agar is too thin or hemolyzed, the reaction may be very weak.

Other CAMP test positive organisms

  1. Listeria monocytogenes
  2. Rhodococcus equi
  3. Vibrio cholerae (certain strains)
  4. Certain species of Corynebacterium.

Reverse CAMP Test

A reverse CAMP test is a reaction whereby hemolysis by the beta-hemolysin of staphylococci is inhibited through the production of phospholipase C or D by organisms such as S. agalactiae, Listeria, Corynebacterium spp., and Clostridium perfringens.

An arrow of no hemolysis is formed at the junction of the organism being tested with the staphylococci if the reverse CAMP test is positive.

References and further readings

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

8 responses to “CAMP Test: Principle, Procedure, Results”

  1. Five Star, your work awesome

  2. Brian says:

    Nice job guys, really helpful

  3. SURANGA MOHOTTIGE says:

    THANKS ITS VERY HELPFUL FOR ME.

  4. Hello sir.; what other organisms apart from grp A streptococcus give CAMP positive?

  5. Dr.R says:

    What is reverse CAMP test ?

  6. ahammed.N says:

    Sir I want a short note on latex aglutina
    tion test and candida albicans

  7. microdoc001 says:

    Hello Dr Acharya, I am glad to inform you that the above picture appeared in the Final FRCPath part2 Medical Microbiology Autumn 2018 practicals exam held on 11/10/2018. Candiates were asked to identify A,B and C, Principles of this test and interpretation of the result.

  8. Samsuddin says:

    Join Whatsapp group for microbiology
    +966 055 25 68 759

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