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 mixture of organisms
living together.
How can we get a certain type of
bacteria?
Pure Culture - separating the progeny of
a single bactium from all others.
Koch - interested in disease causing bacteria (major
contributor to pure culture techniques).
Initially grew bacteria on potato surface but had
problem:
Not enough nutrition for bacterial growth.
Added gelatin as a solidifying agent. (Warm pour, cool - solid)
Streak-plate method - simplest & most
common method to isolate a single bacterium.
Hesse (Koch’s assistant) agar (polysaccharide
extract from marine algae) - easier to work
with then gelatin (solid over a wider range
then gelatin).
Julius Petri - Petri dish
Streak-Plate Method
II. Bacterial growth
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formula to determine
population size:
b = B2n
B= Number of cells at
time zero (beginning).
b= number a cells at
any later time.
n = number of cell
generations.
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A. Growth can be measured
as an increase in mass
(weight) of the population.
B. Growth can be measured
as an increase in cell number.
1. Plate count method count the number of
colonies on the medium.
2. Direct microscopic
count - 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 30C.
2. Four groups of bacteria
based upon their optimum
growth temperatures.
a. Psychrophiles 5C - 20C
b. Mesophiles
20C - 50C
c. Thermophiles 50C - 80C
d. Hyperthermophiles +80C
3. Food Preservation
Refrigerators retards food spoilage because
most of the microorganism that cause
spoilage are mesophiles.
4. Temperature & Human diseases.
Human body
37C (brain, heart, gastrointestinal tract).
20C - 25C (fingertips, ears, feet, hands,
scrotum).
Ex - leprosy (Mycobacterium
leprae)- involves the coolest
regions of the body.
B. Oxygen Requirements
1. Strict Aerobes - require free oxygen to grow.
2. Strict (obligate)Anaerobes - will not grow in the presence of free
oxygen, may even be killed.
3. Micro-aerophilic -prefers the presence of low oxygen (2% - 10%
Oxygen).
4. Facultative Aerobes or Facultative Anaerobes - lives in the presence
of both:
Growth occurs more rapidly in the presence of oxygen.
5. Aerotolerant - 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
hydrogen peroxide (H2O2) & Superoxide (O2-).
Cells that do not die in the presence of oxygen
produce enzymes (Superoxide dismutase) into a
harmless form (H20 & O2).
C. pH
Most bacteria grow best in
an medium with a pH of 7
(neutral).
Can live in a wider range - 5
- 8.
Ex. Helicobacter pylori - live in
very low acidic environments
(humans stomach’s) & may
cause ulcers. Acidophilic.
Bacteria produce metabolic
products that may acidic or
basic.
Need a BUFFER (pH stabilizer)
to grow bacteria.
4. Osmotic Pressure pressure that is
required to prevent
the net flow of water
across the cell
membrane.
Salt concentration
effect water
movement.
Use salt as an growth
inhibiting factor in
food preservation.
IV Cell multiplication requires a source of energy & raw
material for synthesis of cell components.
A. Bacterial Nutrients
Raw Materials
Organic Compounds
Carbon, Nitrogen, Oxygen, Hydrogen.
Inorganic Compounds
all other compounds including ions.
Two Purposes of nutrition
1. Build up (Synthesize) protoplasm.
2. Supply energy to life processes.
B. Energy Source
C. Mineral Requirements
D. Growth Factors
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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.