Chapter 6: Concept of Indicator Organisms and Water Quality

• 2 major reasons for monitoring drinking water quality:

  • Primary assessment - to determine if the water supply system is being operated correctly, implying that the water is safe for consumers.
  • Verification - proof that the water was safe after it was supplied. This includes monitoring for compliance.
• Indicator Organism - the use of an organism that can serve as a surrogate for another.
• Coliforms - are bacteria that are always present in the digestive tracts of animals, including humans, and are found in their wastes. They are also found in plant and soil material.
• • Most coliform bacteria do not cause disease
  • Some rare strains of E.coli, particularly the strain 0157:H7 can cause serious illness.
• E.coli are one of the best indicators for the presence of potentially pathogenic bacteria.
• Common sources of E.coli

  • Bacteria in water can originate from the intestinal tracts of both humans and other warm-blooded animals, such as pets, livestock, and wildlife.
  • Human sources include failing septic tanks, leaking sewer lines, wastewater treatment plants, combined sewer overflow, and boat discharges.
  • Animal sources of fecal coliform bacteria include manure spread on land, improperly disposed farm animal wastes, pet wastes, wildlife, and birds.
• Indicator Organisms

  • Total Coliforms
  • Fecal Coliforms
  • E.coli
  • Fecal Streptococci
  • Enterococci
• Label

  A) e.coli

  B) Total

  C) Fecal

  D) Environmental

  E) Fecal

  F) E.coli

  
• Total coliform test - includes a number of genera and species of bacteria which have common biochemical and morphological attributes that include gram-negative, non-spore-forming rods that ferment lactose in 24 to 48 hrs at 35C.
• Fecal coliform test - a subset of the coliform group of bacteria that can grow at 44.5C (thermotolerant coliforms).

  • There are some thermotolerant coliform species, such as Klebsiella, that are of questionable sanitary significance, thus the test is not an absolute.
• E.coli test - The most recent development in the evolution of the coliform test is the ability to specifically identify and quantify E.coli in water samples through the use of elevated temp and the development of a readily identifiable chemical indicator for the presence of an enzyme system-specific to E.coli.
• Fecal Streptococci test - the feces of humans and animals contain large numbers of streptococcal bacteria that can be classified as belonging to the fecal streptococci group.
• Six species of streptococci:

  • S.faecalis
  • S.faecium
  • S.avium
  • S.gallinarum
  • S.bovis
  • S.equinus
• Enterococci test - are a subset of the fecal streptococci group that includes the first four species of fecal streptococci listed above.

  • This group of streptococci are considered to be more specific as indicators of the sanitary quality of recreational waters than the fecal streptococci group as a whole.