Lab 6 Flashcards
What is the Most Probable Number (MPN)?
A statistical test used to estimate the amount of bacteria formed in a series of dilution tubes based on the cloudiness of the samples of liquid.
What is the MPN used for?
- It is used to estimate the amount of coliform bacteria in a sample indicating the presence of fecal contamination
- It is also used to estimate the amount viable bacteria located in soil, water and agricultural products
Why do we use it?
We use it when material in the sample interferes with being able to generate colonies on petri dish plates for counting by plate enumeration.
How do we conduct experiments to find out what it is?
1) Presumptive test:
-Add 10ml of sample to 5 dilution tubes containing Lauryl Sulfate Trypone Broth and vortex them
-Add 10 ml form the inital 5 dilution tubes to a new set of tubes and vortex them
-Add 10ml from the last 5 dilution tubes and vortex them
-incubate at 37 degrees celsius for 24 hours
-Observe which of the tubes are cloudy mark down the numbers for each set of the 5 tubes and compare to an MPN index
2) Confirmed:
To make sure cloudy tubes are coliform bacteria and not something else.
-Take a loop and stick into cloudy tubes and place into tubes of Brilliant Green lactose broth
-incubate for same time and temperature
- Check to see if BGLB tubes ar ebubbling if so, coliform bacteria are present
-BGLB prevents all other bacteria except for coliform form growing
Completed test: To ensure that the BGLB test was accurate
-take a loop stick into the BGLB tube and use it to streak the Eosin Methylene Blue (ESB) agar
-check to see if a metallic green sheen is present
Can an MPN tell the exact number of coliforms in a sample?
No it can only give an estimate
What’s the Function of a Durham tube is LST broth?
It is used to collect co2 gas indicating the presence of fecal coliform bacteria
Which three media does he use in his completed test in video?
Mackonkey agar -pink coliform colonies Methylene blue agar -metallic green sheen Violet Red bile agar -colonies are red and pink and surrounded by cloudy precipitate
What does it Sorbitol mackonkey agar?
Used to diffrentiate between nonpathogenic strains of Ecoli
