Microlab 8 Review
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20 Terms
What are the three methods to determine if fecal mater is present in a source of water
1- plating method
2- membrane filtration method
3- most probable number (MPN)
What method did we use in class
Most probable number (MPN)
What are the three steps for MPN
presumptive test
Confirm test
Complete test
How many steps did we do
Step 1 and 2
What does the presumptive test include
Inoculate the broth in 0.1 ml of water, 1 mL, and 10 ml, then incubate at 37 degrees Celsius, and wait 48 hrs
What does a positive presumptive test look like
A positive test has gas and growth in the test tube
What is done during the confirm test
Take water from the positive presumptive test and spread on emb plate at 37 degrees. And wait 24 hours
What does EMB test for
Emb test for gram negative bacteria (growth will occur ) and lactose fermenting bacteria (metallic green color)
What is done during the complete test
Take sample from EMB and streak on phenol red lactose agar plate. If it turns yellow then it is acidic and lactose fermenting. Then take a sample from the plate and do gram staining and spot staining. The organism should be gram _ and non spore forming
If you can’t find your MPN on the chart what do you do
Go to the next closest one below it
What are the step to purifying drinking water
Settling of particular matter ( sand)
Filtration (usually though beds of sand)
Disinfection (by chlorine, UV light, or solid chlorine)
How do you treat sewage
Primary treatment- removes solids
Secondary treatment- removes dissolved organic mater(liquid)
Tertiary treatment- chemical process, removal of organic, heavy meatballs ect..
What does portable mean
Drinkable
What is an indicator
Something that is always present in waster like coliform
What were the results from the EMB test
It was gram negative but not lactose fermenting
What are the advantages of MPN
It is a very simple test and has low costs
Whaat are the disadvantages of MPN
It is time consuming and not exactly accurate
What are the advantages of using coliform
It is always present in a sample of sewage, it is easy to grow, and present in large quantities
What are the disadvantages of using Coliform
It can come from many sources, meaning that sewage is necessarily present
What can be used as an indicator for fecal contamination
Coliform bacteria and Fecal streptococci