An Egg White Digest Medium for the Gonococcus. ∗

Abstract

The culture medium described below has been found to yield a more plentiful growth of gonococcus than any we have employed. Additional advantages are transparency, low content of protein, and ease of preparation.

Dissolve 40 gm. of powdered egg white†in a liter of 0.45% NaCl solution and adjust the reaction to pH = 7.0–7.4. Rub into a paste and add to the solution 4 gm. of a special high-test trypsin;‡ plug the mouth of the flask with cotton and incubate on a water bath at 48° C.—with occasional agitation—for 10-12 hours. This temperature prevents spoilage by inhibiting the growth of most micro-organisms. By the end of 10-12 hours, a sample of the digest should give an amino acid titration of 130-180 (i. e., cc. of N/10 NaOH per 100 cc. of digest) by Sörensen's method. This determination is not essential, except as proof that digestion has proceeded satisfactorily, for we have found that a digest with a Sörensen titer of 80 supported growth as effectively as one with a titer of 180.

Now add sufficient HCl to bring the reaction down to pH = 5.0, the isoelectric point of most of the proteins, and autoclave for 15 minutes. Add sufficient distilled water to bring the volume up to its original quantity. Then separate the precipitated proteins by filtration through paper or by centrifugation, and then by filtration through a Berkefeld candle. This sterile filtrate can be stored in the ice-box until needed.

To this clear, straw-colored filtrate add 6 cc. of 0.04% phenol red solution per 100 cc. and readjust the reaction to pH = 7.0-7.2 with NaOH. The indicator in this concentration exerts no bacteriostatic action on the gonococcus, and its addition directly to the digest simplifies the adjustment of pH.