On the Isolation from Agar of an Inhibitor for Neisseria gonorrhoeae

The separation of an inhibitor for Neisseria gonorrhoeae from commercial agars was attempted on the basis of previous work by Mueller and Hinton (1941) and Gould, Kane, and Mueller (1944). In addition, this inhibitor was compared with certain organic compounds of a similar nature by biologic tests of inhibitory activity. Until the medium of Mueller and Hinton (1941) was developed, it was thought impossible to grow N. gonorrhoeae on a simple, well-defined medium, but these investigators showed that casein hydrolyzate, meat extract, agar, and starch supported growth of the organisms as well as chocolate blood agar or ascitic fluid agar. Gould, Kane, and Mueller (1944) further showed that a fluid medium containing casein hydrolyzate, sodium chloride, magnesium sulfate, and phosphate buffer would support growth of N. gonorrhoeae, and that a similar medium with agar added would fail to grow the organisms. The addition of starch to this last medium again permitted growth, which led the authors to the hypothesis that starch neutralized an inhibitor present in the agar. Frantz (1942) also developed a similar simple fluid medium for a closely related organism, Neisseria intracellularis, and observed inhibition of growth of the organisms upon addition of agar to the medium. The experimental work which follows was begun in order to prove the hypothesis of inhibition of N. gonorrhoeae by agar, or a substance in it, that was proposed by Gould, Kane, and Mueller.