Use of tetrazolium for improved resolution of bacteriophage plaques.

Most phages form plaques which, when prepared by the agar-layer technique (M. H. Adams, Bacteriophages, Interscience Publishers, Inc., New York, 1959), are sufficiently pronounced to permit their accurate enumeration under appropriate conditions of illumination. Other phages, however, are difficult to detect and enumerate because their plaques are small or excessively turbid, or both. Phage 83, employed for the genetic analysis Baldwin, J. Bacteriol. 82:875, 1961). After incubation of the assay plates for 8 hr at 37 C, the plaques were sufficiently developed to be scored (Fig. 1). The assay plates containing the fully developed plaques were then flooded with 10 ml of Trypticase Soy Broth (TSB, BBL) containing 0.1% 2,3,5 -triphenyltetrazolium chloride (TTC, Nutritional Biochemicals Corp., Cleveland, Ohio). After incubation at 37 C for 20 min, the broth was