Differential Tests for the Colon‐Aerogenes Groups

Abstract

indications of the presence of the members of the aerogenes group of bacteria, a group closely related to the colon group, in water supplies have long been a source of controversy among bacteriologists. This group has many reactions very similar to the colon group, and, therefore, it is somewhat difficult to separate them. Some hold that the presence of members of either of these groups in water supplies is sufficient evidence for the condemnation of the supply for drinking purposes. As late as 1923, the official method for the determination of the potability of a water supply did not take into consideration the separation of these two groups. 1923 edition of the Standard Methods of Water Analysis (2) made the following statement: It is recommended that the B. coli group be considered as including all non-spore-forming bacilli which ferment lactose with gas formation and grow aerobically on standard solid media.7' last edition (3) does not attempt to separate the two groups as may be seen by the following statement: The formation of gas in lactose broth and the demonstration of Gram-negative non-&pore-forming bacilli in the agar culture shall be considered a satisfactory completed test, demonstrating the presence of a member of the coli-aerogenes group. above definitions give almost equal weight to both the colon and the aerogenes groups of bacteria. If members of the colon group are predominantly of fecal and those of the aerogenes group predominantly of non-fecal origin, such an inclusion is not consistent. In