Experience with Lactose-Bile Medium for the Detection of B. Coli in Water

Abstract

The discovery of B. coli in 1885 by Escherich, coupled with the knowledge that it is a normal inhabitant of the intestine of man and many animals, and therefore is found in sewage and polluted water, has induced water-bacteriologists to pay more attention to its isolation than to any other part of their work. Various methods have been proposed and tried for the detection of this organism in water. The one considered most reliable and meeting with general approval has involved the planting of a portion of the sample, either directly or after revivifying in broth, into plates of lactose-litmus agar; and then putting those colonies developing B. coli characteristics through the different tests as recommended for the identification of this organism. This procedure although accurate, is at the best a slow, tedious, and laborious process. Moreover, it is impracticable when used by the supervisor of a public water-supply, whose duty it is to report on the daily sanitary condition of the water. For example, if two days are required for the water to reach the inhabitants of the city, and it takes seven days to learn the results by this process, the consumer will have used the water five days before he is informed of the danger. To obviate these difficulties, various rapid methods have been proposed and used by different water-analysists. Nearly all are based on the fact that B. coli, when grown in a fermentable sugar, generates a certain amount of gas of which a definite proportion is carbon dioxid. In many cases certain chemicals whose function it is to inhibit the growth of the water bacteria have been added to the sugar solution. The most common is phenol, either alone or in combination with hydrochloric acid. McConkey has recommended the addition of sodium taurocholate to agar; others have used this compound in Smith solution. It would seem that these different methods, all based on the same general principles, ought to give something like concordant results. But unfortunately this is not the case and they