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Microbiology of the Health Sciences

Growth takes place on two levels
◦ Cell synthesizes new cell components and increases
in size
◦ The number of cells in the population increases

The Basis of Population Growth: Binary
Fission
Figure 7.13
–
–
–
–
–
Generation or doubling time: The time required for a complete
fission cycle
Each new fission cycle or generation increases the population by a
factor of 2
As long as the environment is favorable, the doubling effect
continues at a constant rate
The length of the generation time- a measure of the growth rate of
an organism
• Average generation time- 30 to 60 minutes under optimum
conditions
• Can be as short as 10 to 12 minutes
This growth pattern is termed exponential
ATP for cellular processes
Carbon is necessary for the
production of many
macromolecules (proteins, lipids,
and carbohydrates)
Oxygen for metabolism
Nitrogen for amino acid synthesis
Sulfur for vitamins, amino acids,
structural stability of proteins
Phosphorous makes ATP and membranes
Trace elements are used for metabolic reaction in the
cell and cell component stabilization
Co
Mo
Mg
Mn
Ca
Fe
Zn
cobalt
potassium K
molybdenum
magnesium
manganese
calcium
iron
zinc
Organic growth factors such
as vitamins, amino acids, and
nucleic acids some growth
factors cannot be synthesized
by own cellular processes
Water
water activity
Heterotroph: uses organic
carbon source
Autotroph: uses inorganic
carbon dioxide
Phototroph: uses light as energy
source
Chemotroph: uses chemical
compounds (ie. glucose)
Saprobe
Parasite
[INSERT FIGURE 6.1]


Inoculum introduced into
medium (broth or solid)
◦ Environmental specimens
◦ Clinical specimens
◦ Stored specimens
Culture – refers to act of
cultivating microorganisms or
the microorganisms that are
cultivated
[INSERT TABLE 6.3]

Special Culture Techniques
◦ Techniques developed for
culturing microorganisms
 Animal and cell culture
 Low-oxygen culture
 Enrichment culture
Chemically defined
Natural
Living
Enriched Media
added nutrient encourages
the growth of microorganisms
Selective Media
Selects form a microorganism
while inhibiting most others
Phenol Ethanol Agar
Deoxycholate Agar
Differential Media
Allow for the differentiation of
microorganisms based on
action that occurs on the media
or a color change within the
media that is based on a pH
change
Mannitol Salt Agar
MacConkey Agar
What type of media is
Blood Agar considered?
A.
B.
C.
Enriched
Selective
Differential
•
•
•
A population of bacteria does not maintain its potential growth rate
and double endlessly
A population displays a predictable pattern called a growth curve
The method to observe the population growth pattern:
– Place a tiny number of cells in a sterile liquid medium
– Incubate this culture over a period of several hours
– Sampling the broth at regular intervals during incubation
– Plating each sample onto solid media
– Counting the number of colonies present after incubation
–
–
–
–
–
Generation or doubling time: The time required for a complete
fission cycle
Each new fission cycle or generation increases the population by a
factor of 2
As long as the environment is favorable, the doubling effect
continues at a constant rate
The length of the generation time- a measure of the growth rate of
an organism
• Average generation time- 30 to 60 minutes under optimum
conditions
• Can be as short as 10 to 12 minutes
This growth pattern is termed exponential
Data from an entire growth period typically
produce a curve with a series of phases





Lag Phase
Exponential Growth Phase
Stationary Growth Phase
Rapidly Declining Phase
Death Phase
•
•
•
•
•
Relatively “flat” period
Newly inoculated cells require a
period of adjustment,
enlargement, and synthesis
The cells are not yet multiplying at
their maximum rate
The population of cells is so
sparse that the sampling misses
them
Length of lag period varies from
one population to another




When the growth curve increases
geometrically
Cells reach the maximum rate of
cell division
Will continue as long as cells have
adequate nutrients and the
environment is favorable
The number of cells growing
greatly out number the number of
cells dying.

The population enters a survival
mode in which cells stop growing
or grow slowly
◦ The rate of cell inhibition or
death balances out the rate of
multiplication
◦ Depleted nutrients and oxygen
◦ Excretion of organic acids and
other biochemical pollutants
into the growth medium
◦ The number of cells growing will
equal the amount of cells dying.
◦ Endospores begin to form in
this phase.




The curve dips downward
Cells begin to die at an
exponential rate
The amount of cells dying out
numbers the amount of cells
growing.
The dead cells become nutrients
for the growing cells.



The curve continues to dips
downward
Most cellular activity stops
Endospores are formed and
released from the parent cells.
Basic phases of growth:
1. Lag phase: new growth
medium, period of delay while
cells prepare to divide
2. Log phase (exponential growth
phase): cellular reproduction
most active during this period,
generation time reaches a
constant minimum
3. Stationary phase: state of
equilibrium where number of cell
deaths equals number of cell
divisions
Basic phases of growth:
4. Rapidly Declining Phase:
cells die logarithmically,
endospores formed
5. Death phase: number of
deaths exceeds number of
new cells
•
•
•
•
Implications in microbial control, infection, food
microbiology, and culture technology
Growth patterns in microorganisms can account for the
stages of infection
Understanding the stages of cell growth is crucial for working
with cultures
In some applications, closed batch culturing is inefficient, and
instead, must use a chemostat or continuous culture system
•
•
The data from growing bacterial populations are graphed by
plotting the number of cells as a function of time
– If plotted logarithmically- a straight line
– If plotted arithmetically- a constantly curved slope
To calculate thesize of a population over time:
Nf = (Ni)2g
– Nf is the total number of cells in the population at some
point in the growth phase
– Ni is the starting number
– g denotes the generation number
Nf = Ni (2)g
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