Based on the metachromatic property of Toluidine Blue 0, three, convenient agardiffusion methods have been developed that enable detection of the nuclease of Staphylococcus aureus at concentrations as low as 0.005 ,ug/ml in agar and broth cultures. The interactions of agar and deoxyribonucleic acid with Toluidine Blue 0 are discussed.

A rapid, reliable, and simple method based on the binding of crystal violet (CV) is described for differentiating virulence-plasmid-bearing strains of Yersinia enterocolitica from their plasmidless derivatives. As with other plasmid-mediated properties of this organism, the binding of CV occurs at 37°C but not at 25°C. The CV-binding technique provides a simple and efficient means of screening Y. enterocolitica for virulence and for identifying individual plasmid-bearing colonies.

A simple, efficient method for identification and differentiation of Yersinia enterocolitica containing virulent plasmid-bearing clones is described. The method is based on temperature of incubation and the low calcium response of the organism in an agarose Congo red medium.

A simplified procedure to detect the calcium dependency of virulent plasmid-bearing strains of Yersinia enterocolitica was developed. A low-calcium, agarose-based medium of brain heat infusion with added magnesium effectively differentiated plasmid-bearing and plasmidless isolates. Further, the expression of calcium dependency in plasmid-bearing strains of Y. enterocolitica as measured by the average colony diameter was proportional to the calcium concentration of the assay.