Lab: Bacterial examination of water and water purification systems

Question 1

In bacterial examination of water, what is tested for?

Answer 1

an indicator microorganism like E. coli which is not found in uncontaminated soil and water so could indicate likelihood of fecal contamination

Question 2

Why is E. coli a good indicator of fecal contamination?

Answer 2

1. occurs primarily in intestines of humans but not typically found in soil and water
2. can be easily identified by microbiological tests
3. not as fastidious as other intestinal pathogens so it survives longer in water samples

Question 3

What is a coliform?

Answer 3

gram-negative
facultative anearobic
non-endospore forming rods
ferment lactose to produce acid and gas at 35 C after 48 hours
eg. E. coli, E. aerogenes

Question 4

3 tests done to determine coliform count of water

Answer 4

1. presumptive: 15 tubes of lactose inoculated, positive tubes compared to table and result in most probable number of coliforms in 100ul of sample
2. confirmed: Levine EMB plates inoculated from positive tubes to see if orgs are gram-negative acid-producing coliforms
3. completed: orgs from positive agar plates put into lactose broth and incubated for detection of gas production

Question 5

water purification methods

Answer 5

• boiling (may not remove robust pathogens or paticulate matter)
• filtering (expensive)
• chemical treatments (remove most organic material)

Question 6

What can be used as a bioindicator

Answer 6

live orgs that monitor environmental conditions
- Photobacterium phosphoreum: lives in marine environments and produces enzyme luciferase; in presence of O2 produces light
the more light, the less toxic the chemical