New medium for the production of cholera toxin by Vibrio cholerae O1 biotype El Tor

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Abstract
A new medium that stimulates in vitro production of cholera toxin by V. cholerae O1 El Tor (El Tor vibrios) was developed. The medium contains 0.5% NaCl, 0.3% NaHCO3, 0.4% yeast extract, and 1.5% Bacto-Peptone. El Tor vibrios were cultured in a stationary test tube at 37.degree. C for 20 h. The culture supernatant was assayed for cholera toxin by a reversed passived latex agglutination method. Most vibrios grown in this medium produced 10-20 times more toxin than in traditional syncase medium. The number of live vibrios at the end of culture was about 108/ml in the new medium (AKI medium) and about 1010/ml in the syncase medium. As a result, each individual organism in the new medium should have produced as much as 1,000 times more toxin than in syncase medium. Sodium bicarbonate was found to be the most important factor in toxin production by El Tor vibrios in the new medium. This new medium is recommended because of its high yield of cholera toxin and its technical simplicity.