Use of Chinic Acid in the Differentiation of the Colon‐Aerogenes Groups

In 1911, Beijernick called attention to the fact that some strains of Bact. aerogenes produce a red to black coloration in a medium containing chinic acid and a ferric salt, this taking place under aerobic conditions. Strains of Bact. coli, he says, do not color the medium under similar conditions. In such a medium, under anaerobic conditions a fermentation may occur with some members of the aerogenes group in which carbonic, acetic and propionic acids are formed. An attempt was made by the writer to duplicate this anaerobic type of fermentation by organisms of the colon aerogenes group, but without success. Both Smith and Durham tubes were used, but no carbon dioxide was detected. However, the coloration produced by Bact. aerogenes when it grows on chinate medium under aerobic conditions was found to be pronounced. The color produced is soluble and diffuses through the medium in both solid and liquid. It was thought that this observation of Beijernick might be used as a possible differential test for colon-aerogenes strains. The laboratory tests usually employed for the differentiation of the coli and aerogenes sections are the Voges Proskauer and the methyl red reactions. Both of these are classified as color reactions and require a medium consisting of dextrose, peptone and phosphate. There are other tests which may be considered supplementary to the Voges Proskauer and methyl red reactions. Thus, in considering the coli sections the gas ratio CO2/H2 is nearly 1:1 and indol usually positive. The aerogenes section shows a gas ration CO2/H2 of 2:1 and indol usually negative. Another interesting differential test is that of Koser (1922). He states that Bact. aerogenes will produce abundant growth in a medium in which a sodium, potassium or ammonium salt of citric acid is the sole source of carbon. The citric acid medium will not support the growth of Bact. coli.