[Validation of DNAse reaction for identification of Staphylococcus aureus strains in routine mastitis diagnosis]

In routine mastitis diagnostic S. aureus strains are often identified using DNAse reaction. However, this enzyme activity is not limited only to S. aureus strains. Furthermore, the strength of the DNAse reaction between different strains varies strongly. These factors lead to the fact that the results are often not comparable between laboratories. The aim of these investigations was to validate the DNAse reaction for routine identification of S. aureus in mastitis diagnostic and to set a critical limit for interpretation of DNAse reaction. The results of 189 strains isolated from bovine mastitis milk samples show that colonies with beta delta or delta-haemolysis and DNAse reactions of > or = 2 mm can reliably be identified (sensitivity 91.2%, specificity 96.9%) as S. aureus.