Studies of a bacteriophage active against a chromogenic Neisseria.

Cultures and media. Of the 36 strains of Neisseria employed in this study, two strains (155B and 157) were obtained from Dr. S. E. Branham, National Institutes of Health; one strain (10555) from the American Type Culture Collection; one strain (W) from Dr. D. Walcher, Riley Memorial Hospital, Indianapolis, Indiana; and one (B) from Dr. W. Burrows, University of Chicago. Eight strains (1707, 1711, 1712, 1713, 681, 682, 683, and 684) were Lilly stock strains. The remaining strains were recent isolates from human nasopharyngeal washings. These latter strains were classified according to pigment production and carbohydrate fermentation (Breed et al., 1948) with the exception of four atypical strains (Kl, B3, GB1, and K4), which were designated Neisseria species. The cultures were maintained on a glucose starch agar (Difco) to which had been added 0.1 per cent cysteine hydrochloride and 0.5 per cent yeast extract (NM V). Two basal liquid media were used with or without the addition of one or more salts. A concentrated nutrient broth (NB) contained 1 per cent dehydrated nutrient broth (Difoo). The second liquid medium (NM XX) contained cysteine hydrochloride, 1 g; proteose peptone S 3 (Difco), 15g; glucose, 2g; NaCl, 5 g; Na2HPO4 7H20, 5.6 g; yeast extract (Difco), 5 g; and soluble starch, 10 g, in 1 L of distilled water, and was adjusted to pH 7.2. Additions of salts to the basal media were made by adding those with univalent cations as the dry salts prior to sterilization and those with divalent