REPLACEMENT OF NICOTINIC ACID REQUIREMENT OF SHIGELLA SONNEI BY PYRIDINE-3-SULFONIC ACID

blood in the natural or the "chocolate" state with the addition of vancomycin (7.5 ,ug per ml of medium) and streptomycin (20 jAg per ml), was an excellent medium for the isolation of these organisms. As part of a project following the development of the oral flora in infants and children, plates of both types of blood agar containing the respective amounts of vancomycin and streptomycin have been included among the different media routinely inoculated with scrapings from teeth (oral plaque material). These and other plates to be cultured were incubated at 37 C for 3 to 4 days in an atmosphere of 90 ca hydrogen and 10% carbon dioxide. The typical colonies obtained are shown in Fig. 1. By reflected light, leptotrichia appear as rough, whorled, colorless, flat, "Medusa head" colonies (B 2, C 2, and D 2). Fusobacteria form either raised, convex, glistening, speckled, creamcolored colonies (A) or colorless, shiny, flat. spreading colonies (B 1, C 1, and D 1). We have cultured over 200 samples on this medium, which is highly selective for fusobacteria and leptotrichia; only occasionally were colonies of Bacteroides and Neisseria species observed.