A Protein-Free Medium for Primary Isolation of the Gonococcus and Meningococcus

It is desired to report the development of a transparent, reproducible medium, containing no heat-labile material such as serum, which is sufficiently stable to withstand autoclave sterilization and storage, and which will support satisfactory primary growth of either meningococci or gonococci. The latter were used as the test organisms during the experimental work, since a constant source of primary cultures of the meningococcus is ordinarily not available. The similarity between the two organisms, and the reputedly greater difficulty expected in the cultivation of the gonococcus, indicated that a medium suitable for this organism should prove equally satisfactory for the meningococcus. As a basis for comparison, the Difco “Proteose No. 3 Chocolate Agar” has been used. This medium has been adopted as a standard in certain laboratories for the diagnosis of gonorrhoea and one of us (J.H.) was thoroughly familiar with its use. The plan as formulated in beginning the experiments was essentially that followed with considerable success with other organisms, namely, to select the most suitable empirical medium available and attempt to break it down to its essential component parts. The experience of the senior author in 1918 with the Gordon and Hine pea meal extract agar for meningococcus carrier detection had shown that this medium, when carefully prepared, was eminently satisfactory. It proved, upon trial, to be equally so for primary cultivation of the gonococcus, and it was therefore chosen as the starting point in the investigation. It consists essentially of a tryptic digest of meat, agar, and a 5% NaCl extract of pea flour, the latter presumably supplying some essential protein material. The fractionation of the pea extract proved surprisingly simple, since it could be accomplished by mechanical means.