EVALUATION OF THE COLILERT TECHNIQUE
Report No FR0132

P GALE, P BROBERG & G STANFIELD

SEPT 1990

SUMMARY

I OBJECTIVES

To compare the Colilert Test with the Minerals modified glutamate multiple tube fermentation (MMG-MTF) and membrane filtration (MF) standard methods for their abilities to:

  1. detect the presence or absence of total coliforms and E coli;

  2. enumerate total coliforms and E coli; in both untreated and chlorinated water samples.

II REASONS

In monitoring the quality of both drinking and recreational waters, more rapid bacteriological analysis procedures would have advantages in safeguarding public health. Without independent assessment, new procedures cannot be adopted as standard methods. The Colilert Test has generated much interest amongst water microbiologists and as a consequence WRc has performed an independent evaluation.

III CONCLUSIONS

The most probable number (MPN) of total coliforms and E coli were determined using both the Colilert Test and the MMG-MTF standard method.

Statistical analysis of the Colilert Test and MMG-MTF standard method paired counts showed the Colilert Test for E coli to be significantly less sensitive in both the enumeration and detection of the presence of E coli.

Although a larger number of presence/absence discrepancies for total coliforms resulted from the Colilert Test registering an absence, statistically the Colilert Test cannot be rejected as being less sensitive compared to the MMG-MTF standard method.

Statistically, there was no significant difference between the Colilert Test and MMG-MTF standard method in ability to enumerate total coliforms.In 66 of the chlorinated water samples, total coliforms and E coli were also quantified by the MF standard method. For both total coliforms and E coli, the larger proportion of the presence/absence discrepancies arose from the MF standard method registering a negative. However, statistically there was no difference in the abilities of the two methods to detect or enumerate both total coliforms and E coli.

IV RECOMMENDATIONS

If its use would bring operational advantages, the Colilert Test could be used for detecting or enumerating total coliforms in water samples. However, on the basis of the results obtained in this trial it cannot be recommended for presence/absence testing or enumeration of E coli in water samples.

V RESUME OF CONTENTS

This report presents the results of an independent evaluation of the Colilert system for detecting (presence/absence) and enumerating total coliform bacteria and E coli. The principles of the Colilert system are described and details are given on the way in which the trial was conducted. A total of 158 samples were analyzed for total coliforms and E coli using both the Colilert and standard UK most probable number procedures. In addition, 66 of the chlorinated samples were analyzed using the UK recommended membrane filtration procedures. The relative performances of these methods were assessed both in terms of their ability to detect and quantify coliforms and E coli. Although the techniques performed similarly superficial examination of the results suggested that the Colilert system may be less efficient than the traditional procedures. As a consequence, the data obtained have been analyzed by nonparametric statistical procedures to test the null hypothesis that the Colilert Test is comparable to the traditional methods of analysis. The results of this statistical analysis are discussed and some comment made on the way in which results from previous trials have been presented in the literature.

Copies of the Report are available from FWR, price 15.00 less 20% to FWR Members