Report No DWI0331

June 1987


This report describes work in the period April 1985 to May 1987 on the Department of the Environment's research contract Improved Methods of Bacteriological Sampling and Analysis (Reference PECD 7/7/160).

Methods for rapidly detecting and enumerating bacteria are well established in the food and pharmaceutical industries and have many clinical applications. Although these methods could offer manpower, time and cost savings in the analysis of water their adoption into routine use has been hindered by lack of evaluation and their incompatibility with existing procedures. This report evaluates the application of several rapid bacteriological techniques to water quality monitoring and assesses the needs for sample storage and preservation procedures.

Two commercially available instruments (the Bactometer and the Malthus Growth Analyser) which detect bacteria by measuring changes in the electrical properties of culture media have been evaluated The performance of test procedures developed by the instrument manufacturers and WRc for detecting coliform bacteria in recreational and drinking waters was assessed. The advantages and disadvantages of the techniques are discussed as is their potential role in routine water quality monitoring.

A rapid means of confirming the presence of E. coli by detecting the presence of the enzyme, Beta-glucuronidase, has been evaluated. A method in which this test is combined with the traditional membrane filtration procedure to give confirmed E. coli counts in 18 h is described.

The results of the studies with the Beta-glucuronidase test and electrical techniques are being used to prepare detailed test procedures. These will be submitted for approval as "tentative procedures" for incorporation in the next edition of Report 71.

Determination of the adenosine tri-phosphate (ATP) content of water samples and direct counting of bacteria by epifluorescence microscopy have been investigated as replacements for the standard plate count technique. Using suitable concentration and resuscitation procedures concentrations as low as four organisms per ml could be detected by ATP measurement. Although a working, direct-count procedure was developed automated counting of the bacteria by image analysis proved infeasible.

Study of the effect of storage on the bacterial content of water samples was hindered by many problems which could not be overcome during the period of the contract. The problems encountered, results obtained and a recommendation for future approaches to this problem are discussed.

Overall conclusions based on the studies are given as are recommendations for further research.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.