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.