Lab: Water Testing Flashcards
(24 cards)
What is the common procedure for conducting water quality tests?
Test water for bacterial indicators of fecal pollution.
What are the two groups of indicators used in water testing?
- Coliform bacteria
- Escherichia coli
What are the characteristics of coliform bacteria?
- Gram-negative rods
- Catalase positive
- Oxidase negative
- Ferment lactose with gas formation
Which genera are included in the coliform group?
- Escherichia
- Enterobacter
- Klebsiella
- Citrobacter
What does the presence of coliform bacteria indicate in water testing?
Potential contamination in developed countries where water is chlorinated.
Should coliform bacteria be present in finished water?
No, they should not be present.
What is the significance of Escherichia coli in water testing?
It is the main indicator of fecal contamination if water is not chlorinated.
How many E. coli are typically present in human feces?
Approximately one hundred million E. coli per gram of feces.
What is the first step in the presumptive test procedure?
Mix water sample thoroughly.
In the presumptive test, how much of the water sample is transferred to the lactose broth tube?
2 ml.
What indicates a positive test result in the presumptive test?
Any yellow tubes with gas formation.
What is the purpose of the confirmed test following the presumptive test?
To confirm positive results as some organisms may produce acid and gas in lactose broth.
What type of agar is used in the confirmed test to distinguish between coliforms?
EMB agar.
What two coliforms can be distinguished using EMB agar?
- Escherichia coli (sewage)
- Enterobacter aerogenes (soil or vegetation)
What should be done after labeling the EMB plate?
Incubate for 24 hours.
What should be recorded after the incubation of the EMB plate?
Class results.
What do E. coli colonies appear like on a plate?
Dark with a green metallic sheen
E. coli is a common indicator of fecal contamination in water.
How do E. aerogenes colonies differ from E. coli colonies?
Larger, runny, and have a dark center
E. aerogenes is another type of coliform bacteria, often found in the environment.
What is the first step in confirming the presence of coliforms?
Inoculate a tube of lactose broth and a nutrient agar slant
This step is essential for further testing of the bacteria.
What indicates a positive completed coliform test?
Gas formation in lactose broth and Gram negative, non-spore forming short rods
These characteristics are typical of coliform bacteria.
What tests should be completed from the slants on Day Four?
Gram stain, catalase test, and oxidase test
These tests help identify the biochemical characteristics of the bacteria.
What should be included in the laboratory notebook under RESULTS?
Charts and/or pictures of results from each test (presumptive, confirmed, and completed)
Documenting results is crucial for analysis and understanding of the experiments.
What conclusions should be drawn regarding the origin of microbial flora in natural water?
Discuss the origin and why E. coli is used as an indicator species
E. coli is often used due to its presence in fecal matter and its reliability as an indicator.
Could glucose be used instead of lactose for the presumptive test for coliform bacteria? Explain.
This is not a simple yes or no answer; consider metabolism
The metabolic pathways of bacteria differ, affecting their growth on various sugars.
