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

  • Bastian Schnabel

    Student thesis: Doctoral Thesis


    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® 8090™, Proteus mirabilis ATCC® 43071™, and
    Salmonella Typhimurium ATCC® 14028™ 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.
    Date of AwardJul 2018
    Original languageEnglish
    Awarding Institution
    • University of Brighton
    SupervisorJonathan Caplin (Supervisor) & Ian Cooper (Supervisor)

    Cite this