Testing the waters : evaluation of a novel medium for the detection and enumeration of Escheria coli under field conditions in the developing world

Background and aims: With regard to human involvement in the water cycle, the detection and quantification of faecal indicator bacteria is regarded as a fundamental measure of water quality. Commercial test kits for assessing bacteriological water quality in developing countries have been criticised for their complexity and their requirement for equipment and resources. Conversely, some of the simpler presence-absence methods (e.g. H2S test) have a lower sensitivity and specificity when compared to conventional tests. Methods: A novel medium (Coliblack) has been formulated, based on defined substrate technology, using the chromogen 8-hydroxyquinoline-beta-D-glucuronide to detect Escherichia coli, where a positive result gives the same strong colour reaction as the H2S test. Other features of the Coliblack medium include the use of tergitol as a selective component that gives enhanced recovery of injured bacteria, plus the addition of sodium pyruvate as a peroxide-neutralising resuscitative agent. Results: Coliblack proved to be effective in the quantitative recovery of injured cells of E. coli under laboratory conditions, and also gave similar results to standard UK and US media in 96-well MPN assays of environmental water samples. Field trials of a simple multiple-tube MPN format in villages in Punjab, India showed that this novel medium was easy-to-use, with positive feedback from all participants in the trials. Conclusions: Coliblack combines the desirable advanced technical features of high sensitivity and specificity with the practical advantages of ease-of-use under field conditions, enabling it to play a role in water quality monitoring at the household level.