Bacterial enumeration - Dilutions and Plate counts Flashcards
Blank Describes individual colonies on a plate’s surface
Colony forming unit
The number of individuals doubles each generation
Exponential growth
Cloudiness of a fluid caused by large numbers of particles/organisms
Turbidity
The measure of the light intensity absorbed by a sample
absorbance
Asexual reproduction resulting in two daughter cells
Binary Fission
Order the steps for performing a dilution series
Determine the dilutions of the dilution tubes.
Determine the dilutions of the agar plates.
Determine which plate is the countable plate.
Calculate the concentration in the original tube.
True/False: Binary fission is a method of sexual reproduction where a single cell (parent cell) will split into four cells (daughter cells).
False –> 2 daughter cells
Define viable plate count
A common method used to determine the number of organisms in a culture
Define colony forming unit (CFU).
Each colony on a plate
How many CFUs for the plate to be considered viable.
30 - 300 CFUs
What is the dilution formula?
Dilution = Volume of sample added mL/ Total volume (mL of Sample + mL of Diluent)
If 1 mL of sample is added to 9mL of diluent, what is the dilution?
Dilution = 1/ 1+9 = 1/10
What are successive dilutions?
Dilutions that are multiplied together to determine the final total dilution.
Dilution of 3rd tube
= 1/10 x 1/10 x 1/10 = 1/1000
How to determine the number of CFUs in the original plate.
The number of colonies on the viable plate is multiplied by the total dilution factor. For example, if it is determined that there are 57 CFUs on a plate that was diluted 1000 fold, then the original culture would have contained 57,000 CFU/mL.
True/False: If there is more than one plate for a dilution, the CFUs of all the plates that have that dilution are averaged together prior to multiplying by the dilution factor.
True
True/False: If more than one dilution that falls within the 30-300 CFU range, only the least diluted plate is used in the calculations.
True
To determine the number of CFUs in the original culture, the number of colonies on the viable plate is _____ the total dilution factor of that plate.
Responses
Multiplied by
Step 1: Determine the dilutions of the dilution tubes (first series of dilutions). In the example, 0.5 mL is removed from the original tube and is added to 4.5 mL of sterile diluent to create a 1:10 dilution. In this example, each of the subsequent tubes created are also 1:10 dilutions.
Dilution of 1st tube = 0.5mL/5ml = 1/10
Step 1: Determine the dilutions of the dilution tubes (first series of dilutions). In the example, 0.5 mL is removed from the original tube and is added to 4.5 mL of sterile diluent to create a 1:10 dilution. In this example, each of the subsequent tubes created are also 1:10 dilutions.
Find dilution of 3rd tube
0.5mL/5mL x 1/10 x 1/10 = 1/1000
Step 2: Determine which plate is the countable plate.
What is a countable plate?
30 - 300
Step 3: Calculate the concentration in the original tube.
How do you do this?
Number of colonies counted should be divided by final dilution of plate.
Concentration of original tube = Colonies counted/ dilution X volume
Which plate should you count?
Plate A = 500 colonies
Plate B = 50 colonies
Plate C = 100 colonies
Plate C bc it is least diluted.
Binary fission is a method of sexual reproduction where a single cell (parent cell) will split into four cells (daughter cells).
True/False
False
Order the steps for performing a dilution series.
1.) Determine the dilution of the dilution tubes
2.) Determine which plate is the countable plate
3.) Calculate the concentration in the original tube
What is a colony forming unit and how is it used to infer microbial numbers in a sample?
A colony is group of microorganisms grown on a single agar plate. Colonies are used to estimate the microbial numbers in a sample by multiplying the visible number of colonies by the dilution factor to provide a CFU/mL result.
A viable plate has a count of 95 colonies produced from 0.125 mL of a 10-4 dilution of the original sample. The original contains _____ CFU/mL.
7,600,000
Determine the Concentration of the original sample.
Dilution plate CFU = 120
Dilution factor of viable plate = 1/1000
Volume of diluent added to plate = 0.125mL
CFU/mL original = 0.96 = 120/(0.125) x 1000
In binary fission, bacterial cells grow _____
Exponentially
When one bacterial cell undergoes binary fission, there will be _____ cells present on the 5th generation.
16
A viable plate count is a method of calculating the number of cells in a dilution by the counting the number of _____ on agar plates.
colonies
Performing a 1:8 dilution from the original sample 3 times would produce a dilution of _____.
1: 512
True or False
To create a series of dilutions, an identical volume of stock (undiluted) solution is added to each of the dilution test tubes.
False
