A cultural phenomenon produced by most streptococci in Lancefield Group B. Called after the originators Christie, Atkins and Muench-Petersen. These streptococci hemolyze red cells in sheep blood agar plates but only in the presence of beta toxin of staphylococci. The phenomenon is used to presumptively diagnose the presence of Streptococcus agalactiae in mastitic cow's milk. Similar synergism in hemolytic activity is observed between Rhodococcus equi and Corynebacterium pseudotuberculosis, beta toxin of staphylococci or Listeria monocytogenes, and can be used for presumptive diagnosis of these species.
