New Method for Detection of Coliform Organisms

Abstract

estimating the extent of coliformorganism contamination of water supplies, a presumptive test medium containing lactose is usually utilized in the examination, because the coliform group ferment lactose rapidly with the production of acid and gas, thus serving as a useful pollution index. Hajna (1) proposed, in 1951, a buffered desoxycholate lactose broth for use as either a presumptive or confirmatory medium in the examination of water and food. The inclusion of sodium desoxycholate was to inhibit growth of sporeformers and other Gram-positive bacteria without affecting the growth of coliform organisms. Gas production in the broth was abundant in most cases, sometimes being even greater than in the standard lactose broth. Occasionally, however, only small amounts of gas were noted in both media when incubated for 48 hr, owing to the presence of slow lactose fermenters. McCrady (2) has stated that the majority of laboratory workers are opposed to excluding from the coliform group the slow lactose fermenters, which usually ferment glucose with a large amount of gas. In view of this, the question arose as to whether a buffered broth containing glucose and incorporating sodium desoxycholate, as a presumptive medium, would not be more suitable than that containing lactose for the examination of water.