Influence or incubation temperatures on differential tests of coliform bacteria.

In the bacteriological testing of rural raw water supplies the laboratory is having to face, constantly, the problem of evaluating the sanitary significance of the atypical coliform bacteria so often recovered from positive tests. For several years the author and associates have carried on studies of these bacteria as a corollary to the water-testing service that is maintained for the rural public of the state. A review of some of these studies has been published (Fuller, 1944). The study here reported is another in the series. The object was to determine the reactions of coliform bacteria, recovered from raw water, to differential tests at incubation temperatures ranging from the conventional 37 C to the Eijkman temperature of 46 C. The hope was that the information gained would be of help in determining the relation of atypical or intermediate coliform bacteria to fecal or nonfecal types. The Eijkman (1904) test has not had popular support in recent years among sanitary bacteriologists in this country. Its use in modified form, however, has been recommended by Perry and Hajna (1933, 1935) for detecting coliform bacteria, particularly Escherichia coli, in shellfish. Their experience prompted some work in this laboratory by France (1938) and Levine (1940). France observed that certain coliform strains were able to produce acid, but not gas, in lactose broth at 46 C, and Levine found that certain strains produced gas at higher incubation temperatures in the modified Eijkman medium of Perry and Hajna (1933) than in the lactose broth of the Standard Methods. These experiences suggested the study which is the subject of this paper.