Water & Enviro Week 6

Waterborne diseases

Due to ingestion of water contaminated by pathogens

How can waterborne disease spread

Ingestion of faecal contamination from infectious person

Water washed diseases

Insufficient water for washing and personal hygiene - caused by bacteria

Water based diseases

Due to pathogens that spend part of their life cycle in water or aquatic organisms

How does water based disease occur

ingestion of eggs or skin penetration of worms

Water related diseases

Caused by pathogens which are spread by insects that breed or feed near water

To prevent disease we have to…

Ensure water is not contaminated with pathogens

Pathogen monitoring is impractical because

1. Pathogens are outnumbers by other bacteria

2. Large volumes of water have to be filtered

3. Time consuming

Faecal indicator organisms

Presence indicate human faecal contamination & potential for pathogenic organisms

Coliform bacteria

Make up about 10% of intestinal bacteria of humans and animals

Total coliforms

Found in soil and vegetation

Faecal coliforms

Sub group of total coliforms - more accurate indicator of animal or human waste

E coli

Sub group of faecal coliforms - can cause illness

Most probable number / Multiple tube method

Detects and enumerates coliforms using presumptive & confirmatory tests

Presumptive test

Prepare dilutions, add samples to test tubes, incubate at 37 degrees for 48 hours, tubes then tested for acid and gas production

Acid and gas indicate ______ Acid / gas presence is indicated by

Presumptive coliform result, colour change

Confirmatory tests

Tubes with acid & gas production inoculated into more selective media

Membrane filtration

Known volume of water sample passed through 45um membrane filter which retains bacteria present - filters examined giving results in 18h

Defined substrate techniques

Growth of coliforms in colourless defined media produces colour changes (yellow)

Drawbacks of coliform test

1. Regrowth after testing can occur

2. Not directly indicative of a health threat

3. No correlation between coliforms and pathogen numbers, including viruses