Transcript Bacterial Growth - Belle Vernon Area School District

Bacterial Growth
I. Determine in terms of population size.
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Nature there is a
of
organisms living together.
How can we get a certain type of
bacteria?
- separating the progeny of a
single bacterium from all others.
- interested in disease causing bacteria
(major contributor to pure culture techniques).
Initially grew bacteria on potato surface but had
problem:
Not enough
for bacterial growth.
Added gelatin as a solidifying agent. (Warm pour, cool - solid)
- simplest & most
common method to isolate a single bacterium.
Hesse (Koch’s assistant)
(polysaccharide
extract from marine algae) - easier to work
with then gelatin (solid over a wider range
then gelatin).
Julius Petri -
Streak-Plate Method
II. Bacterial growth

formula to determine
population size:
b = B2n
= Number of cells at
time zero (beginning).
= number a cells at
any later time.
= number of cell
generations.
Review
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Why is agar used instead of gelatin or potato?
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Why is the petri dish unique to prevent
contamination?
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What is the advantage of bacterial growing by
binary fission? What is the disadvantage?
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How many bacteria will there be after 10 hours
if the bacteria double every 30 m inutes?
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A. Growth can be measured
as an increase in
(weight) of the population.
B. Growth can be measured
as an increase in
.
1.
count the number of
colonies on the medium.
2.
- counting the
number of bacterium in
an known volume of
liquid.
III. Factors that influence microbial
growth.
A. Temperature
1. Most bacteria grow within
or near
.
2.
groups of bacteria
based upon their optimum
growth temperatures.
a.
b.
c.
d.
5C - 20C
20C - 50C
50C - 80C
+80C
Review

Describe the difference between direct count
and plate count method.
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What are the three temperate ranges that
bacteria tend live in?
3. Food Preservation
Refrigerators
food spoilage because
most of the microorganism that cause
spoilage are
.
4. Temperature & Human diseases.
Human body
37C (
20C - 25C (
).
).
Ex - leprosy (Mycobacterium
leprae)- involves the
regions of the body.
Review
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Why do we store our food in refrigerators?
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Why do you not want to keep heating and
cooling the same leftover throughout the week?
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Which temperature range to most tend to live
in and why?
B. Oxygen Requirements
1.
- require free oxygen to grow.
2.
- will not grow in the presence of free oxygen,
may even be killed.
3.
-prefers the presence of low oxygen (2% 10% Oxygen).
4.
- lives in the presence of both:
Growth occurs more rapidly in the presence of oxygen.
5.
- will grow in the presence of oxygen
but do not posse an oxidative metabolism:
Derive no benefit from the presence of oxygen.
Why can some bacteria thrive in the presence of
oxygen but others are killed by it?
Oxygen can be converted into a toxic form like
(H2O2) &
(O2-).
Cells that do not die in the presence of oxygen
produce enzymes (
)
into a
form
(H20 & O2).
C. pH
Most bacteria grow best in
an medium with a pH of
(neutral).
Can live in a wider range
Ex. Helicobacter pylori - live in
very
environments
(
) & may
cause ulcers.
Bacteria produce metabolic
products that may acidic or
basic.
Need a
(
to grow bacteria.
)
4.
pressure that is
required to prevent
the net flow of water
across the cell
membrane.
effect water
movement.
Use salt as an
factor
in food preservation.
IV Cell multiplication requires a source of energy & raw
material for synthesis of cell components.
A. Bacterial Nutrients
Raw Materials
Carbon, Nitrogen, Oxygen, Hydrogen.
all other compounds including ions.
Two Purposes of nutrition
1.
2. Supply energy to
(Synthesize) protoplasm.
.
B.
C.
D.
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Small organic molecules other than carbon that bacteria
must provide in order to grow (amino acids & vitamins).
V. Dynamics of population
growth.