Simplified method for detecting faecal coliform in water

Abstract

MFC medium was modified as modified presence-absence faecal coliform test for detecting faecal coliform in water by replacement of rosolic acid with 0.035% bromocresol purple. Ten-ml modified medium was used for 100-ml water sample. The results of this modified method were detected in two aspects, colour- and pH-changes. The standard multiple tubes fermentation technique (FT) was used as the reference method. Eighty-two water samples from natural traditional drinking water (deep well, pipe, rain, pond and shallow well) were collected. They were examined for the faecal coliform by both the reference and the modified techniques. Comparison of the FT, modified presence-absence faecal coliform (colour) [mP-A FC(colour)] and modified presence-absence faecal coliform(pH) [mP-A FC(pH)] tests by McNemars test showed that (e) the FT and mP-A FC(pH) tests did not differ significantly for natural waters (p > 0.05 and p > 0.01), (ii) the FT and mP-A FC (colour) tests did not differ significantly fior deep well, piped and rain waters (p > 0.05) but differed significantly for pond and shallow well (p<0.05), and (iii) the FT and mP-A FC(colour) tests did not differ for deep well, piped, rain and shallow well waters (p > 0.01) but differed significantly for pond (p < 0.01). In terms of validity and efficiency, the FT was the most valid and efficient test. The mP-A FC(pH) was more sensitive and more efficient but was less specific than the mP-A FC(colour) test. Identification of isolates showed that (i) E. coli was the most dominant species in natuiral water samples by the FT technique, and in pond and shallow well waters by the mP-A FC(colour) test, (ii) Enterobacter species was the most dominant species in deep well, piped and rain waters by the mP-A FC(colour) test, and (iii) E. coli was isolated from all types of water by both the FT and mP-A FC(colour) tests. The faecal coliforms isolated were Citrobacter freundii, E. coli, Enterobacter cloaceae, Enterobacter aerogenes, Edwardsiella tarda, and Klebsiella pneumoniae. Several advantages of the mP-A FC tests were: (i) high sensitivity and specificity, (ii) ease of media preparation and examination, (iii) less time-consuming, and (iv) more feasible than the FT technique appoximately thee times. Suggestions from this study are: (i) the mP-A FC test should be applied as a screening test in the field for examining the faecat coliform contamination in drinking water, (ii) the mP-A FC(pH) test should be used to examine waters taken from deep well, rain, pond. piped and shallow wells, (iii) the mP-A FC(colour) test should be used to examine waters taken from deep well, piped, rain and shallow wells, (iv) the mP-A FC (colour) test would be useful for the Water Quality Surveillance Programme in rural areas, and (v) the mP-A FC test should be modified further in order to increase its sensitivity and efficiency.