Studies on the Extracellular Enzymes of Staphylococci

The authors studied usefulness of the deoxyribonuclease test as an aid in the identification of pathogenic staphylococci with reference to the constitution of medium and criteria for determination.The constitution of the test agar divised by the authors was heart infusion agar added with 0.2% of DNA and 0.045% of CaCl2. Addition of NaCl in more than 0.5% to the medium proved to inhibit the DNase production of staphylococci. The most appropriate time to determine the reaction was shown about 15 minutes after pouring 1.5N of HCl onto the plate cultivated at 37°C for 18 hours.Using the above test medium, 395 strains of staphylococci freshly isolated from various sources of clinical specimens were investigated the DNase activity in comparison with coagulase production and several other biological properties: 193 strains of coagulase-positive staphylococci were all DNase-positive and 202 strains of coagulase-negative ones DNase-negative with exception of 8 strains.Furthermore, the correlation between DNase activity and coagulase production was found to be the closest among all the biological attributes of the strains tested. Thus it may be concluded that the DNase test agar divised by the authors is also useful for identification of pathogenic staphylococci isolated in this country.