Dominick-Lauter Medium Compared with Standard Lactose Broth for B. Coli Tests

Abstract

Bacteriologists, sanitarians, water plant operators, and all others connected with any phase of the drinking water problem are interested in any method of water examination or analysis that will produce dependable results in a shorter period of time. The American Public Health Association through its committee on Standard Methods has adopted a scheme of examination of water samples that is usually referred to as the Standard Method (1), and the standard procedure for determining the presence of B. coli in water, is to use lactose broth prepared according to their recommendations as an enrichment medium followed by confirmation. This confirmation is time consuming and postpones for 24 to 96 hours the time in which a reliable report may be rendered. The troublesome feature of the standard lactose broth has been that with certain water supplies, especially treated supplies, gas is produced in the presumptive tests by certain organisms or groups of organisms that are not members of the colon group. These may be spore bearing anaerobes or certain organisms that have the faculty of fermenting lactose when growing in symbiotic relationship with other organisms, but, since they are not necessarily of fecal origin they have little significance in water purification, and since gas formation is observed in these samples time must be consumed in determining whether the causative organism is a member of the colon group. Even after time has been spent in attempting this differentation our results are not always conclusive as we frequently fail to find B. coli when present due to overgrowth by accompanying species. Dominick-Lauter (2) have developed an enrichment medium for the examination of water samples that seems to offer hope that the time consumed in making an examination can be materially reduced. This medium has the same basic composition as the standard lactose broth, but with the addition of certain buffer salts and inhibitive dyes.