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Microbiology Dilutions
Theory and Practice
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What are they for?
For many years,
scientists have used aserial dilution method to
control sample size.
This is important tomany diagnostic and
enumeration methods.
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Key Terms Sample: refers to the original liquid
that will be tested. If a rinse of a
chicken skin is being tested, what is the
sample?
Diluent: the solution that is mixed withthe sample (often purified water).
Concentration: refers to how much ofthe sample is in a given test. For
example, 40 to 1 (1/40) dilution
means that for every 40 parts of water,there is 1 part of sample.
Dilutions are given in terms ofconcentration.
The liquid from the rinse is
the sample.
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Pitcher of Juice
For example, this is
100% pure juice.
So the
concentration is
1 to 1, or 1/1.
Or in other words,
this is a one to
one dilution.
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Concentraon Volume
And even if wewere to pour it
into a glass, its
still 100% juice in
that container.
Even though it ismade up of many
ingredients, juice
is our sample.
Still 1/1 Dilution.
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Serial Dilution
1.) Serial Dilution starts witha primary sample.
Dilution = 1/1
2.) If we take 10 ml ofthat sample and put itin an empty tube, it is
still the sameconcentration.
Dilution = 1/1
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Serial Dilution
But for dilutions, these other tubes are filled with 9 ml of water.
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Serial Dilution
1 ml
We then transfer 1 ml of the original solution into the tube with9ml of water.
Tube #2 now has 10 ml of liquid.#1 #5#4#3#2 1 ml SAMPLE + 9 ml H2O = 10 ml
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Serial Dilution
1 ml
Tube #2 now has 10 ml of liquid.
#1 #5#4#3#2
1 ml SAMPLE + 9 ml H2O = 10 ml
We then transfer 1 ml of the original solution into the tube with9ml of water.
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Serial Dilution
#1 #5#4#3#2
Now, tube #1 is still completely the originalconcentration. (1/1 Dilution)
Tube #2 has 10 ml, of which 1 mlis sample. (1/10 Dilution)
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Serial Dilution
#1 #5#4#3#2
1 ml
1 ml is then taken from tube #2, and mixed into tube #3
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Serial Dilution
1 ml
1 ml is then taken from tube #2, and mixed into tube #3
#1 #5#4#3#2
1/1 1/10
Tube #3 now has 9 ml of water, and 1 ml from tube #2
9 + 1 = 10 ml
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Test Yourself
#
1
#
5
#
4
#
3
#
2
1/1 1/10
What is theconcentration intube #3?
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Lets Work It OutTo find the concentration of tube #3, we multiply:
the previousconcentration(tube #2)
1
10 x1
10
Units transferred(ml)
over
Total units in newcontainer
=
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Lets Work It OutTo find the concentration of tube #3, we multiply:
the previousconcentration(tube #2)
110
x 110
Units transferred(ml)
over
Total units innew container
=
1
100
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So if we continue the process
#1 #5#4#3#2
1/1 1/10 1/100 1/1,000
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So if we continue the process
#1 #5#4#3#2
1/1 1/10 1/100 1/10,0001/1,000
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So if we continue the process
#1 #5#4#3#2
1/1 1/10 1/100 1/10,0001/1,000
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Consistent Formula
#1 #5#4#3#2
1/1 1/10 1/100 1/10,0001/1,000
Previousconcentration
x
Unitstransferred
Total
units
=New
Concentration
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But whathappens when
we messeverything up?
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TEMPO Problems
TEMPO vials = 4 ml
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Find the Final Dilution:
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Find the Final Dilution:
1
1
1
4
x
1
100
1
4x
=
=
1
4
1
400
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Always Remember
Previous
concentrationx
Unitstransferred
Totalunits
=New
Concentration
1.) Concentration Volume
2.) Follow the formula
