Notes on the Determination of B. Coli in Water

Abstract

The number of these organisms in a water supply has a considerable range, from a few hundred per c.c. in a grossly polluted water, down to practically none in some springs and deep wells, surface water under occasional conditions, and the effluent of a filter of high efficiency. When they are frequently present, the determination of the number of acid-forming colonies developing upon the litmus lactose agar plate of Wurtz gives an indication sufficient for all practical purposes of the polluted condition of the water. When they are quite absent from a water it is a simple matter to demonstrate the fact with reasonable certainty. The complications and the refinements in the determination of the presence of this organism are brought out in a long-continued routine examination of waters which lie between the two limiting classes, that is, in which the most delicate tests show B. coli to be sometimes absent and sometimes present, but in numbers too small for direct determination. Especially is refinement in this work necessary in determining the sanitary efficiency of a filter, under conditions which may bring forth critical inspection of the results obtained. In the work of this laboratory we have accumulated a mass of data obtained in carefully conducted coli work, and we present it here in statistical form, with certain observations upon the various factors of the work, for the benefit of others engaged in similar studies.