A comparison of standard lactose broth with lauryl sulphate broth and with the Eijkman method for demonstrating fecal coliform bacteria.

Lauryl sulphate broth, introduced by Cowles (1938) and modified by Mallman and Darby (1941), has been widely used in recent years for the presumptive test for coliform bacteria in water. Lauryl sulphate is, to a certain extent, an inhibitory agent and tends to suppress anaerobic lactose fermenting bacteria. Inhibitory agents in culture media are always subject to suspicion. A substance which can be used in a concentration which will both inhibit all the undesired organisms and allow all the desired ones to grow uninhibited, is certainly to be desired but is rarely encountered. There is good evidence that many persons are not entirely convinced that lauryl sulphate in lactose broth lives up to this ideal. Many comparative studies of this medium with lactose broth and other presumptive media have been published and these have been reviewed by McCrady (1943). However, the fundamental question as to the effectiveness in detecting all the fecal coliform bacteria has not been clearly answered. One wants to be assured that all fecal coliform bacteria will produce gas if they are inoculated into lauryl sulphate broth, or at least that as many will produce gas in this medium as in the standard lactose broth. In the same way, one would like a clear cut and convincing answer to the question as to whether or not the Eijkman test as presently modified (Am. Public Health Assoc., 1946) actually does allow the development of any and all the fecal coliform bacteria that are inoculated into the broth. By fecal coliform bacteria we mean simply coliform bacteria from feces, not coliform bacteria that may have or have not, this or that biochemical property. It has been shown that the original Eijkman method allows only a small proportion of the fecal coliform bacteria to grow and produce gas (Skinner and Brown, 1934). At various times the test has been modified by changing the formula of the medium, and by altering the incubation temperature. Various studies, some of them including comparison with other media, have been made (Wilson et al. 1935; Hajna & Perry, 1935; Wilson, 1935; Perry & Hajna,