DNase agar can be used to differentiate between potentially pathogenic S. aureus and other Staphlococcus by looking for the presense of the exoenzyeme DNase. After growth for 24-48 hrs 1N HCL is added to the agar plate. Addition of HCL precipitates DNA in the media causing cloudiness unless the DNA has been hydrolyzed creating a clear zone around the growing colony.
A). Staphlococcus aureus (coagulase +): zone of clearing around the growth after addition of 1N HCL indicating the DNA in the agar has been hydrolyzed. Note: the yellow color of the streak.
B). Staphlococcus epidermidis: growth with no zone of clearing
C). Staphlococcus saprophyticus: growth with no zone of clearing