Modification of the H2S test to screen for the detection of sulphur- and sulphate-reducing bacteria of faecal origin in water

The H₂S test was created to assess the microbial quality of drinking-water in low-resource settings, but the original version of the H₂S test lacks sensitivity and specificity for faecal indicator bacteria. There is evidence that a modified media formula of the H₂S test may be more sensitive and specific for the faecal indicator bacterium Escherichia coli (E. coli) and less sensitive to organisms of non-faecal origin. This research established the detection threshold and operational range of the H₂S test, and to increase its sensitivity and specificity for E. coli. A total of 20 modifications of the H₂S test, and the original test, were assayed against 20 confirmed and pure culture bacteria of faecal and non-faecal origin at varying concentrations. Additionally, some of the H₂S test modifications were evaluated against standard methods for drinking-water analysis. Results indicate that using a modified version of the H₂S test containing L-cystine and 2-mercaptopyridine, and bile salts or penicillin G, E. coli will produce H₂S. In addition, this research reveals which organisms react positively to the original and modified versions of the H₂S test. The modified versions of the H₂S test can be promoted as a simple screening test for microbial drinking-water safety in low-resource settings.