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.

Development and use of single "polytropic" diagnostic tubes for the approximate taxonomic grouping of bacteria isolated from foods, water and medicinal preparations.

Single tubes, containing in all instances a bottom layer of a solid medium for detecting mode of attack on glucose, lactose, mannitol or starch and top layers of solid, semi-solid or liquid media allowing assessment of motility, formation of catalase, oxidase, coagulase, indole, hydrogen sulphide, acetyl methyl carbinol or pigments, as required ("polytropic" diagnostic tubes) were developed for the approximate taxonomic grouping of bacteria commonly encountered in foods, water and medicinal preparations. They are designated as: Gram negative diagnostic tubes (GNT), tubes allowing identification of E. coli, following the principle set out by MCKENZIE, TAYLOR and GILBERT (MTGT), diagnostic tubes for Vibrio parahaemolyticus (VPT), open tubes to assess oxidative attack on glucose (OGT), Gram positive diagnostic tubes (GPT), and mannitol plasma tubes (MPT) for the identification of Staph. aureus. In addition a CP tube for the identification of Cl. perfringens is described, the basis of which is the production of H2S from sulphite in the presence of cycloserine, absence of mitality and failure to produce indole at 46 degrees C. All tubes contain intermediate layers to avoid interactions between changes occurring in top and bottom layers. Upon examination of about 600 pure cultures from collections or freshly isolated from foods etc. such tubes have given results which were in agreement with those of classical testing; in a few instances (testing for indole formation) even better results were obtained. The use of such polytropic tubes in identification routes saving much time and effort is outlines.