Calculate the number of bacteria (CFU) per milliliter or gram of sample
by dividing the number of colonies by the dilution factor
The number of colonies per ml reported should reflect the precision of the method and should not include more than two significant figures.
How do you calculate bacteria?
- Example.
- The mean division time for bacteria population A is 20 minutes. …
- In order to answer this, you can split the calculations into two sections.
- If the bacteria grow for six hours, each bacterium will divide 3 times per hour × 6 hours = 18 times.
How do you find the concentration of bacteria in original sample?
- To find out the number of CFU/ ml in the original sample, the number of colony forming units on the countable plate is multiplied by 1/FDF. This takes into account all of the dilution of the original sample. …
- 200 CFU x 1/1/4000 = 200 CFU x 4000 = 800000 CFU/ml = 8 x 10.
- CFU/ml in the original sample.
How do you calculate dilution of bacteria?
For example, suppose the plate of the 10^6 dilution yielded a count of 130 colonies. Then, the number of bacteria in 1 ml of the original sample can be calculated as follows:
Bacteria/ml = (130) x (10^6) = 1.3 × 10^8
or 130,000,000.
How do you find the concentration of bacteria?
Directly counting blood cells or tissue cells by using
a hemocytometer can determine the concentration of a known volume. Counting the number of colonies that arise on a pour plate can calculate the concentration by multiplying the count by the volume spread on the pour plate.
How do you calculate the number of bacteria in a sample?
Calculate the number of bacteria (CFU) per milliliter or gram of sample by
dividing the number of colonies by the dilution factor multiplied by the amount of specimen added to liquefied agar
.
What is the formula of dilution factor?
Dilution factor is defined as:
total volume of solution per aliquot volume
. Where total volume of solution is: 10.0 + 240.0 = 250.0 mL (volumetric flask.) Note: For multiple dilutions the dilution factor is the product of the dilution factors for each individual dilution.
What is the formula for calculating CFU?
To find out the number of CFU/ ml in the original sample, the number of colony forming units
on the countable plate is multiplied by 1/FDF
. This takes into account all of the dilution of the original sample. For the example above, the countable plate had 200 colonies, so there were 200 CFU, and the FDF was 1/4000.
What is the formula for bacterial growth?
The rate of exponential growth of a bacterial culture is expressed as generation time, also the doubling time of the bacterial population. Generation time (G) is defined as the time (t) per generation (n = number of generations). Hence,
G=t/n
is the equation from which calculations of generation time (below) derive.
What are the two types of bacteria?
There are broadly speaking two different types of cell wall in bacteria, that classify bacteria into
Gram-positive bacteria and Gram-negative bacteria
.
What is the dilution method?
Dilution is
the process of decreasing the concentration of a solute in a solution
, usually simply by mixing with more solvent like adding more water to the solution. … The resulting solution is thoroughly mixed so as to ensure that all parts of the solution are identical.
What is the principle of serial dilution?
Serial dilution is a common technique used in many immunologic procedures. A small amount of
serum or solute can be serially diluted by transferring aliquots to diluent
. One of the most common series doubles the dilution factor with each transfer (1:2, 1:4, 1:8 …).
How do you do a 1 in 100 dilution?
For a 1:100 dilution,
one part of the solution is mixed with 99 parts new solvent
. Mixing 100 μL of a stock solution with 900 μL of water makes a 1:10 dilution. The final volume of the diluted sample is 1000 μL (1 mL), and the concentration is 1/10 that of the original solution.
Which technique is best used to count isolated colonies?
In microbiology,
streaking
is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested.
How do you calculate dilutions?
You use the formula
V1c1=V2c2
. In any dilution, the number of moles of solute stays the same. You are simply increasing the amount of solvent in the solution. Moles = litres×moleslitres = volume × molarity = V×c .
What is a 1 in 50 dilution?
Explanation: If you want to make a 1/50 dilution you
add 1 volume part of the one to 49 parts of the other
, to make up 50 parts in all.
