Comparative study of streptococcal DNase by rapid and quantitative assay systems

Clinical isolates of group A, B, and G streptococci were compared in regard to their extracellular deoxyribonuclease (DNase) activities by the modified assay system for DNase using DNA-methyl green complex as a substrate. DNase activity in a culture supernatant of each strain was measured as a percent decrease in the substrate-specific absorbance at 640 nm. After 1 hr incubation, DNase activities in all the strains of group A streptococci were found to be markedly higher than those of any strain in the other groups, although the DNase activities in groups B and G were considerably heterogeneous. These findings were also seen when commercially available DNA-dye complex reagent for the determination of anti-DNase B antibody titer was used as a substrate in the assay system. Our results suggest that this newly established assay system could be applicable for the rapid measurement of DNase activity to distinguish group A streptococci from the other groups.