Evaluation of the H2S test as an indicator of waterborne fecal contamination Public Deposited

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Last Modified
  • March 20, 2019
Creator
  • McMahan, Lanakila
    • Affiliation: Gillings School of Global Public Health, Department of Environmental Sciences and Engineering
Abstract
  • A major limitation of the H2S test for the detection of fecal bacteria is the current uncertainty and variability of its sensitivity and specificity for bacteria of fecal origin based on data from available studies. The purpose of this research was to determine whether a quantitative H2S test could correctly identify fecally contaminated water samples and determine if there was any relationship between the test results and diarrheal disease risk. Using culture-based biochemical and culture-independent molecular techniques, this research focused on determining the types of microbial community members, including fecal indicator organisms, pathogens, and other microbes present in human sewage samples that are detected in a quantitative H2S test as microorganisms of concern to human health. Sewage waters, natural waters from the United States, and household drinking water samples from central Vietnam were analyzed for the production of H2S producing bacteria. The water sources tested in this study were chosen based on the 2002 World Health Organization Guidelines for Drinking Water Quality to be representative of commonly used drinking water sources worldwide and included a rainwater cistern, a protected lake, a well in an agricultural setting, and a well in a forested area. For the culture-based method, samples were analyzed for the presence of fecal bacteria by spread plating the water sample enrichment culture onto selective agar media. The isolates were then: (1) tested to determine whether they were H2S producing organisms, and (2) identified to the genus and species level using biochemical methods (primarily Enterotube and API 20E). Terminal Restriction Fragment Length Polymorphisms (TRFLP), a quantitative molecular technique developed for rapid analysis of microbial community diversity, was used to identify microbial community members and understand microbial community differences in water samples. Overall, these experiments showed: (1) when a water sample tests positive for H2S, there are fecal bacteria in the water sample; (2) greater than 70 percent organisms isolated by the culture based biochemical identification method were also identified using TRFLP analysis; (3) although community composition differed and changed, there was a fairly stable group of identifiable microorganisms in the water samples; and (4) a quantifiable, low-cost version of the H2S test costing less than 0.75USD had a similar relationship to diarrheal disease as did standard E. coli methods for testing drinking water samples in a developing country.
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  • "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Environmental Science and Engineering, the Gillings School of Global Public Health."
Advisor
  • Sobsey, Mark
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  • Chapel Hill, NC
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  • Open access
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