A simplified procedure for the examination of drinking water for bacteria of public health significance: the differential hydrobacteriogramme.

A new method is described which can be used for the examination of piped drinking water. It is also suitable for monitoring water which was initially of potable quality, and is intended for reuse in the food industry. The method is based on CLARK's "P-A test" and, because this allows many bacterial types to be detected, i.e. Enterobacteriaceae, E. coli, P. aeruginosa, Aeromonadaceae and LANCEFIELD group D streptococci it is called differential hydrobacteriogramme. A preliminary resuscitation treatment to revive sublethally injured cells is essential in this procedure. In earlier work this was attained by adding an equal volume of double strength nutrient broth and later double strength MACCONKEY purple broth, making the method somewhat bulky. In the new procedure, after the resuscitation step, a concentrated bile salts/indicator solution is added, allowing subsequent selective enrichment of the taxa sought. Positive enrichment cultures are examined for these organisms by the procedures summarized in Fig. 1. The new method, when tested on approx. 150 artificially inoculated and 92 natural samples, showed the same productivity and selectivity as the one introduced earlier. The new method is recommended for routine monitoring purposes, because it is less bulky.