A SELECTIVE MEDIUM FOR ORAL FUSOBACTERIA

There have been several reports on the use of special selective media for the isolation of oral fusobacteria. Slanetz and Rettger (1933) used a potato extract agar medium containing gentian violet as a bacteriostatic agent. This medium and various modifications of it have been employed by many other investigators. Spaulding and Rettger (1937b) and B0e (1941) used ascitic fluid, blood serum and various vegetable extracts as enrichments to improve the growth promoting qualities of the potato extract medium. In most instances gentian violet, crystal violet, or brilliant green was added to the medium at concentrations of 1:2,000 to 1:20,000 for selective bacteriostasis. For example, Spaulding and Rettger (1937b) found that the addition of gentian violet at a concentration of 1:20,000 in potato extractcysteine agar gave the most effective medium for the isolation of oral fusobacteria. The fusobacteria have greater resistance to these dyes than many other microorganisms, but inhibition of growth of associated organisms was not always accomplished. In a previous study (Omata, 1951) in this laboratory, in which the inhibitory action of various antibiotics was tested on fusiform bacilli, it was found that certain strains of fusobacteria showed marked resistance to streptomycin and dihydrostreptomycin. In another study (Omata, 1953) it was found that casein digest and yeast extract were essential for excellent growth of oral fusobacteria. A new medium was formulated incorporating streptomycin and crystal violet, and compared with the potato extract-gentian violet medium as to its effectiveness for the isolation of oral fusobacteria from stimulated saliva from humans. This report describes this medium and the results of this comparison.