Difficulty: Easy
Correct Answer: Coliform Most Probable Number (MPN) test
Explanation:
Introduction / Context:Public health surveillance of water supplies relies on indicator organisms that signal fecal contamination and treatment efficacy. Direct routine testing for every pathogen is impractical; instead, coliform bacteria (particularly E. coli) serve as reliable indicators of sanitary quality in distribution systems.
Given Data / Assumptions:
Concept / Approach:The Coliform MPN test estimates the most probable number of coliform organisms per 100 mL using serial dilution and fermentation tubes or membrane filtration counts. The presence/absence and counts of coliforms correlate with the likelihood of fecal contamination and disinfection failures. Heterotrophic plate counts are supplementary process indicators but do not directly indicate fecal pollution.
Step-by-Step Solution:
Collect representative distribution system samples aseptically.Perform MPN or membrane filtration for total coliforms and E. coli as per standards.Interpret results against regulatory criteria (e.g., zero E. coli in 100 mL).Verification / Alternative check:
Cross-check with chlorine residuals and turbidity; spikes in HPC may prompt operational reviews but are not fecal indicators per se.Why Other Options Are Wrong:
Microscopy and heterotrophic plate counts lack specificity to fecal contamination.Identifying all pathogens or universal viral assays are infeasible for routine monitoring.Common Pitfalls:
Relying solely on HPC; ignoring sample preservation and holding times that can alter bacterial counts.Final Answer:
Coliform Most Probable Number (MPN) test
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