This image depicts the results of a reverse CAMP test which involved the growth of bacterial cultures on a medium of blood agar, for a 24hr period, in a CO2-rich environment.
The CAMP test involves a bacterium that produces a ß-lysin (beta-lysin), which partially lyses, or destroys the red blood cells (RBCs) in the medium, which in this case is Staphylococcus aureus, i.e. the central vertical streak. The plate is then inoculated with test subject bacteria, which in this case was Arcanobacterium haemolyticum, formerly Corynebacterium haemolyticum (upper horizontal streak), and Arcanobacterium pyogenes, formerly Corynebacterium pyogenes (lower horizontal streak). Note that these streaks do not touch the central S. aureus streak.
You’ll see that, as expected, the S. aureus produced an aura representing a hemolytic reaction in the blood agar medium. The A. haemolyticum inhibits the S. aureus hemolysis by excreting the protein phospholipase D, which is responsible for the inhibition of the hemolytic reaction (arrow heads). A. haemolyticum is the only Arcanobacterium that is reverse CAMP positive. Note that the A. pyogenes produced a negative reverse CAMP test at the point where its streak intersected the S. aureus streak.