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Title: Modification of the H₂S test to screen for the detection of sulphur and sulphate-reducing bacteria of faecal origin in water
Author: Schnabel, Bastian
ISNI:       0000 0004 7427 0978
Awarding Body: University of Brighton
Current Institution: University of Brighton
Date of Award: 2018
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The original H2S test was developed in the 1980s to assess the microbial quality of drinking‐water in low‐resource settings. This test was promoted as a promising alternative to more sophisticated technologies, as the test can be performed in low‐ resource settings. However, the H2S test lacks specificity for indicator organisms and has never been evaluated by accepted method validation techniques. Despite these criticisms, the H2S test is a popular field test in many less‐developed parts of the world and is promoted by many leading non‐governmental organisations because it is low‐cost, easy to apply, and easy to read. This PhD project investigated the performance of the H2S test and its newly developed modifications, by first establishing the detection threshold of the test and second, by validating the H2S test and its modifications against the internationally accepted membrane filtration method. A final objective was to determine whether a media formulation could be developed to detect Escherichia coli (E. coli). The diagnostic sensitivity and specificity of the H2S test was assessed by correlating its performance against that of the modifications. All tests were incubated at 20, 37and 44°C to ascertain operating parameters. All test variants were analysed against 20 pure‐cultured bacterial species in order to identify those capable of triggering a positive result. The research shows that it is possible to detect the faecal‐indicator E. coli by using an adaptation of the original H2S test. The five strains of E. coli were able to produce H2S in the presence of organic sulphur compounds. The original H2S test produced positive reactions for Citrobacter freundii ATCC® 8090TM, Proteus mirabilis ATCC® 43071TM, and Salmonella Typhimurium ATCC® 14028TM only. Modifications developed during this research enhanced the sensitivity and specificity to E. coli when the source of sulphur was changed from thiosulphate to L‐cysteine, L‐cystine, or 2‐mercaptopyridine. The inclusion of bile salts, penicillin G, and L‐cystine increase the diagnostic sensitivity and specificity for faecal coliforms. Furthermore, modified versions showed a comparable level of diagnostic sensitivity and specificity (100%) with the standard membrane filtration method using m‐FC media. The data presented in this thesis demonstrate that the H2S test variants developed during this research can be used as a screening test for the assessment of microbial drinking‐water safety, in low‐resource settings.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available