DNAse Agar
DNAse agar contains free DNA in the media.  Some organisms are able to release exonuclease enzymes which breaks the DNA down into free nucleotides which can then be taken up by the cell.  After growth 1 N HCl is added to the plates.  The HCl reacts with any DNA that has not been broken down and causes the media to become slightly cloudy.  If the organism has used some of the DNA there will be a zone of clearing around the areas of growth.  DNAse agar is commonly used to detect staphylococci, streptococci and Serratia (Enterobacteriaceae).