Water Quality Analysis

Water Quality Analysis: Agents and Sources of Waterborne Diseases

  • Waterborne diseases are caused by various pathogens, leading to different illnesses. (Refer to Table 32.1)
  • Common transmission sources:
    • Potable water: Used for drinking and cooking; undergoes extensive treatment (filtration, chlorination).
    • Recreational water: Public ponds, lakes, swimming pools, etc.
  • Water quality in the U.S. is reported monthly to the EPA, as mandated by the Safe Drinking Water Act.

Public Health and Water Quality

  • Screening water for every pathogen is impractical due to cost and the potential for safe-looking water to contain numerous organisms.
  • Potable and recreational water are routinely tested for specific indicator organisms.
    • The presence of these organisms signals potential disease.
  • Coliforms as Indicator Organisms
    • Coliforms serve as indicator organisms.
    • Not all coliforms are fecal.
    • Coliform testing isn't a reliable indicator for viral pathogens.
  • Fecal Coliforms
    • Fecal coliforms are utilized in water safety testing.
    • Escherichia coli (E. coli) is a key fecal coliform.
    • Enterococcus faecalis is another indicator organism but not a coliform.

Coliforms

  • Characteristics:
    • Gram-negative, non-endospore forming rods from the Enterobacteriaceae family.
    • Oxidase negative.
    • Glucose fermenters.
    • Nitrate reducers.
  • Lactose Fermentation
    • Lactose fermenters with gas production.
    • Noncoliforms: Lactose non-fermenters tend to be pathogenic.
  • Measurement
    • Measure the growth of organisms recovered from water samples.
  • Common Enumeration Methods
    • Most Probable Number (MPN) procedure.
    • Media containing ONPG and MUG.
  • Commercial products:
    • Colilert ®
    • Compact Dry EC
    • Petrifilm
  • E. coli Distinction
    • E. coli can be distinguished from total coliforms with defined substrates.

Testing for Coliforms and E. coli via Most Probable Number (MPN) Method

  • (Day 1) Presumptive test
    • MPN index
  • (Day 2) Confirmed test
    • EMB agar
  • (Day 3) Completed test
    • NA (TSA) slant
    • Lactose broth
  • Procedure: Day 1 (Presumptive Test)
    • Collect various water samples to be tested.
    • Inoculate each sample into nine lactose broth tubes.
    • Repeat for the other samples.
    • Incubate for 24 - 48 hours
    • Tubes:
      • DSLB (10 mL each)
      • SSLB (1 ml each)
      • SSLB (0.1 mL each)
      • Positive control: undiluted
      • Negative control: 10-1 10-2

Results of Presumptive Test (MPN)

  • Positive Tube Count
    • Count the positive tubes.
    • Positives are turbid with gas in the Durham tubes.
    • This count gives the MPN code.
  • MPN Index Determination
    • Determine MPN index (concentration) by comparing the code with the MPN chart.
      Example
    • MPN code: 3-2-1
    • MPN index: 150 per 100mL (Range 30-440)

Colilert® Test

An alternative to MPN

  • Reagent contains ONPG and MUG.
  • Coliforms utilize β-galactosidase to metabolize ONPG, changing it from colorless to yellow.
  • E. coli uses β-glucuronidase to metabolize MUG, creating fluorescence.
  • The Reagent is mixed with 100ml of water to be tested, then incubated for 24-48 hours.
  • Results:
    • Negative: No color change, no fluorescence.
    • Coliform Positive: Yellow color.
    • E. coli Positive: Fluorescence under UV light.