Often when inoculating a BAP to observe hemoloysis patterns, investigators will also stab several times through the agar using an inoculating loop. This stab allows for the detection of streptolysin O, a specific hemolysin produced by Streptococcus pyogenes. This hemolysin is inactivated by O2 and is only seen subsurface (in an anaerobic environment) around the stab mark. Note the oval-shaped areas of clearing around the stab marks in the picture below; these are caused by streptolysin O.