Water Analysis and Coliform Bacteria

Water Analysis

• Water analysis is crucial for identifying pathogenic bacteria in water sources.
• Common challenges include the low numbers of individual pathogens and the time required to isolate and detect them.
• Water pollution by fecal contamination is a significant concern due to the presence of pathogens in small concentrations and the large number of possible pathogens.
• It is not practical to test for every pathogen, so indicator organisms, like coliform bacteria, are used to indicate fecal contamination.
• Indicator organisms are microorganisms that are not naturally found in water and are present only when fecal contamination occurs.
• Their density is proportional to the degree of contamination, with higher density indicating more pollution.
• Indicator organisms provide indirect evidence of pathogen presence, with a focus on coliform bacteria as a common indicator.
• The minimum burden for coliform bacteria is 10 coliforms per 100 ml of water.

Coliform Bacteria

• Coliform bacteria are aerobic or facultative anaerobic, gram-negative bacilli.
• They are non-spore forming and ferment lactose with acid production.
• Some coliform bacteria can produce gas (hydrogen sulfide).
• Thermotolerant coliforms can grow at 44 or 44.5ºC.
• Examples of thermotolerant coliforms include Escherichia coli, Citrobacter freundii, Enterobacter, Klebsiella pneumoniae, and Serratia.
• Total coliforms include bacteria found in soil, surface water, and human or animal waste.

Water Analysis Methods

• The Multiple Tube Fermentation Method is used to assess total and fecal coliforms in drinking water.
  • It involves a series of dilutions and incubations with lactose fermentation tubes.
  • Positive reactions are indicated by fermentation of lactose, producing acid and gas.
  • The method consists of three stages:
    • Presumptive Test: Dilution from a water sample is added to lactose fermentation tubes.
    • Culture: Samples from positive presumptive tubes are streaked onto EMB (Eosin-Methylene Blue) agar.
    • Completed Test: Isolated lactose-positive colonies from EMB are inoculated into lactose broth and nutrient agar slant.
• The Membrane Filtration Method involves filtering a measured volume of water through a membrane with a pore size of 0.45 mm.
  • Bacteria trapped on the membrane grow into colonies, allowing for bacterial density calculation.
  • Filters for fecal coliform detection are incubated at 44.5°C for 22-26 hours.
  • mEndo agar LES is a selective and differential growth medium used to detect total coliforms.
    • It contains lactose and a pH indicator that changes color when acid is produced.
    • Coliforms produce a metallic (golden) sheen due to aldehyde and acid production from lactose fermentation.
    • Some total coliforms may have dark red, mucoid colonies or a dark center without a metallic sheen.
  • mFC agar is used to detect fecal coliforms.
    • It contains bile salts that inhibit bacteria other than fecal coliforms.
    • Rosolic acid, a pH indicator, turns dark blue when acid is produced, identifying lactose-fermenting bacteria.
    • Fecal coliforms form blue colonies, while E. coli forms flat dark blue colonies.

Escherichia Coli (E. coli)

• E. coli is a member of the Enterobacteriaceae family, possessing β-galactosidase and β-glucuronidase enzymes.
• It grows at 44-45°C on complex media, fermenting lactose and mannitol with acid and gas production.
• It produces indole from tryptophan.
• Some strains can grow at 37°C but not 44-45°C, and some do not produce gas.
• E. coli does not produce oxidase or hydrolyze urea.
• E. coli is considered the best indicator of fecal pollution and potential pathogen presence.

This quiz explores the importance of water analysis in identifying pathogenic bacteria, particularly focusing on coliform bacteria as indicator organisms for fecal contamination. It highlights the challenges of detecting individual pathogens and the role of coliforms in assessing water quality. Test your knowledge on these crucial concepts in environmental science.