What Is the CAMP Test?

A Christie, Atkins, and Munch-Peterson (CAMP) test is a way for microbiologists to test for the presence of a particular type of bacteria in a sample called Group B Streptococci. It is a visual test that involves a growth medium with a blood ingredient, a known type of bacteria, and the sample. The blood breaks down in a distinctive fashion, leaving areas of growth medium that appears translucent, because if Group B Streptococci are present in the sample, they produce a protein called CAMP factor that interacts with the other type of bacteria involved.

This test is named for the scientists who first discovered it in 1944, and therefore the test bears their names, or more commonly, their initials. Historically, microbiologists noticed that different types of bacteria grew on varying forms of media in a distinctive manner, because individual bacterial species are typically specialized to use certain nutrients and live in certain conditions, although some are more amenable to others to changing environments. In the case of the CAMP test medium, this is a petri dish filled with a solid agar mixture that contains a range of nutrients and blood from a cow or a sheep.

An analyst streaks a line of bacteria in a line down through the center of the plate. This bacteria is a known strain of Staphylococcus aureus that laboratories can buy that only contains cells of that particular strain and no other bacteria. These bacteria can break down sheep or cow blood cells for use as food. After some time in an incubator that keeps the bacteria warm and help them to grow, this strain of S. aureus produces a translucency underneath the area where the analyst placed the bacteria at the beginning of the incubation. This visible translucency is due to a protein called beta hemolysin that the bacteria produce that breaks down the cells and the red coloration of the cells.

When CAMP factor, which is a protein produced by Group B Streptococci, comes into contact with beta hemolysin, the effect of both of them together makes more translucent areas than would otherwise be the case. The basis of the CAMP test is that when an analyst streaks a little line of a sample that potentially contains Group B Streptococci, at right angles to the central line of S. aureus, but not touching the central line, then any CAMP factor present will make a distinctively shaped zone of translucency. A positive CAMP test shows an arrow-shaped area of translucency at the end of the second, horizontal line.

This represents the area where the beta hemolysin and the CAMP factor overlapped, and had more of an effect on the breakdown of the blood cells than either of the proteins would individually. Apart from research purposes, the reason for performing the CAMP test may be to identify the presence of Group B Streptococci in a sick person, as this group of bacteria are important human pathogens. Variations on the CAMP test include a system of checking for the presence of a certain strain of Listeria, and another test for the presence of a particular type of Clostridium.