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Microbiology – Alcamo
Growth and Growth Phases
Growth
•
Human Terms:
Growth = Larger
•
Microorganism Terms:
Growth = More
Growth
• Binary Fission – bacteria reproduce
asexually:
– Chromosome duplicates
– Cell elongates
– Plasma membrane pinches in at center
– Nuclear material distributes evenly
– Cell wall thickens to separate dividing
cells
Growth
• Binary fission – gives immortality to
bacteria
• The first bacterium never dies
• It reproduces and becomes a new,
young cell again
• The original bacterium (billions of years
old) is still among us
Binary Fission United
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Growth
Reproduction
Binary Fission
20 Generation
21 Generation
22 Generation
23 Generation
Generation Time
•
Time between cell divisions when
bacteria grows and develops its
unique features
•
Also called “Doubling Time”
•
A determining factor in the amount
of time that passes between entry of
an organism into our bodies and the
appearance of disease symptoms
Growth
•
Each microorganism has it’s own
characteristic generation time
•
Range:
– Usually 1 to 3 hours
– Minimum 20 minutes (E. coli)
– Maximum 33 hours (T. pallidum syphilis)
BACTERIAL GROWTH IS
LOGARITHMIC
Growth
Growth Rates
• If after 48 hours of incubation, a colony
is pinpoint size, long GT is indicated.
• If after 48 hours, the colony is ¼” wide,
short GT is indicated.
Growth Example
E. coli has a 20 minute generation time
under ideal conditions:
Time
# of Bacteria
0
1
1 hour
8
2 hours
64
3 hours
512
10 hours
> 1 billion
36 hours
Cover face of the earth
Growth
Growth Rates
•
Exponential growth signifies ideal
conditions and maximum
reproduction
•
But the reproductive potential of
bacteria is never fully realized due to
environmental limitations
Growth Phases
• Many dynamics affect the population of
bacteria over the course of time
• A certain population’s history may
begin when:
– Several bacteria enter the human
respiratory tract
– Several bacteria are transferred to a tube
of growth medium in a lab
Growth Phases
Lag Phase:
•
First few hours of growth curve
•
Period of adjustment to new
environment
•
If an infection, WBC’s can be
engulfing some cells
•
If in a lab, some cells may die from
transfer shock
Growth Phases
• The activity of the remaining cells is
intense as they:
– Store nutrients
– Synthesize enzymes
– Prepare for binary fission
• But the curve remains at a plateau,
where the number of cells reproducing
equals the number of cells dying
Growth Phases
Log Phase:
•
Also called “exponential” phase
•
The mass of each cell increases
rapidly and reproduction follows
•
As each generation time passes, the
number of bacteria doubles and the
graph rises quickly
Bacterial Growth
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Growth Phases
• In humans, disease symptoms arise
during the log phase
– Bacterial population is high enough to
cause damage
– Fever, coughing, tissue damage arise
• In a lab, visible signs of growth will be
seen:
– colonies will appear on solid media
– broth media will become cloudy
Growth Phases
• Research experiments are usually done
during the log phase because the
population of bacteria is at its
maximum potential
Growth Phases
Stationary Phase:
•
Period of even population numbers
•
Reproduction rate = death rate
•
No change in total number of bacteria
Growth Phases
• Stationary Phase:
• In humans:
– the immune system may be destroying the
bacteria
– antibiotics have been administered
• In the lab:
– nutrients are becoming scarce
– waste products are building up
– oxygen or water could be in short supply
Growth Phases
Decline Phase:
•
Environment becomes progressively
worse and exerts its limiting powers
–
pH is changing
–
oxygen and nutrients are scarce
–
accumulation of toxins
Growth Phases
•
Decline Phase:
•
Number of cells dying exceeds the
number of new cells formed
–
Spore forming species will start to
produce spores
–
Flagellated species will try to move to a
new location
–
For other species, culture death is
eminent
Things That Affect Growth
Temperature
• Different species grow at different
temperatures
– Psychrophiles – grow best between 0oC
and 20oC
– Mesophiles – grow best between 20oC and
20oC
– Thermophiles – grow best between 40oC
and 90oC
Things That Affect Growth
Temperature
• Most bacteria are Mesophiles,
especially pathogenic bacteria that
grow in the human body (37oC)
• When the body’s temperature rises to
40oC (104oF) there is a slightly negative
affect on bacterial growth
• The lab incubator is set at 37oC to
encourage bacterial growth
Things That Affect Growth
Temperature
• Some mesophiles can grow at
refrigerator temperatures and cause
food spoilage
• Staphylococci can grow in the
refrigerator and deposit their toxins on
cold cuts, salads and leftovers
• If these foods are eaten without further
cooking, food poisoning can result
Things That Affect Growth
Temperature
• Salmonella outbreak in a restaurant in
1991
• Restaurant employee prepared Caesar
salad dressing which contains raw egg
• It may have remained at room
temperature too long before being
served
• Within 3 days, 15 people were ill with
diarrhea, fever, cramps and vomiting
Things That Affect Growth
Oxygen
• Aerobic bacteria – require oxygen to grow
• Anaerobic bacteria – require an oxygenfree environment to grow
– Includes Clostridium species that cause
tetanus and botulism
• Facultative bacteria – grow in either the
presence or absence of oxygen
– includes many staphylococci, streptococci
and bacilli
Things That Affect Growth
pH
• Bacteria have a neutral internal
environment
• Will tolerate a pH range of 6.5 – 7.5
• Human blood and tissues have a pH of
~7.2 – 7.4
• Provides a suitable environment for
disease causing bacteria to grow
Things That Affect Growth
pH
• Certain bacteria are acid-tolerant
• Useful in the food and dairy business
• Lactobacillus and Streptococcus produce
the acid that converts:
– milk to buttermilk
– cream to sour cream
– milk curds to cheese
• These bacteria pose no threat to good
health even when eaten in large quantities
Things That Affect Growth
pH
• Most bacteria do not grow well under
acidic conditions
• Stomach’s acidic environment prevents
disease
• Certain acidic foods are hardly ever
contaminated with bacteria
– Citrus fruits
– Cabbage
– Tomatoes
Things That Affect Growth
Pattern of Nutrition
• Bacteria (like us) need:
–water
–foods to serve as energy sources
and as raw materials for
synthesis of cell components
Things That Affect Growth
Pattern of Nutrition
• Two patterns for obtaining nutrition:
– Autotrophy – can make their own food
using inorganic carbon, water and sun’s
energy
– Heterotrophy – obtain preformed organic
molecules from the environment for
structural components and energy
• Saprobes – feed exclusively on dead organic
matter such as rotting wood
• Parasites – feed on living organic matter such
as human tissues
Things That Affect Growth
Bacterial Cultivation
• In the lab, bacteria are grown in:
– nutrient broth containing water, beef
extract and peptone (protein supplement)
– nutrient agar – contains the same, plus
agar, a polysaccharide derived from
marine algae
*Most bacteria grow well in these
Things That Affect Growth
Bacterial Cultivation
• Some bacteria require enriched or
specialty media
• The streptococci that cause strep
throat and scarlet fever grow well when
whole blood is added to the media
• Blood agar – heated before
solidification to disrupt the red blood
cells and release hemoglobin
• Sometimes called chocolate agar
Things That Affect Growth
Bacterial Cultivation
• Selective media – contain ingredients
to inhibit the growth of certain bacteria
in a mixture while promoting the
growth of others
– Mannitol salt agar – high salt content
inhibits the growth of most bacteria, but
allows for staphylococci to grow
– Eosin methylene blue agar – contain dyes
that inhibit Gram-positive bacteria, but
allow growth of Gram-negative
Things That Affect Growth
Bacterial Cultivation
• Differential Media – makes it easy to
distinguish colonies of one organism
from colonies of another on the same
plate
• MacConkey’s agar contains red dyes as
well as lactose
– Colonies of bacteria that ferment lactose
are red
– Colonies of bacteria that don’t ferment
lactose are colorless
Things That Affect Growth
Bacterial Cultivation
• Natural Media – not chemically defined
– Exact components and quantities are not
known
– Some bacteria will only grow on natural
media
• Synthetic Media - chemically defined
– The nature and amount of each component
is known
Things That Affect Growth
Intermicrobial Relationships
• Symbiosis – situation in which two
populations of organisms interact in a
close and permanent association
• Benefits obtained may involve:
– food
– protection
– support
Things That Affect Growth
Intermicrobial Relationships
• Mutualism – symbiosis that benefits
both populations
• Bacteria living on roots of plants:
– Bacteria trap nitrogen for plants to
synthesize amino acids
– Plants provide a stable environment and
growth factors for bacteria
Things That Affect Growth
Intermicrobial Relationships
• Commensalism – one population
receives benefit from the relationship
while the other is not helped or harmed
• Bacteria that inhabit human skin:
– Bacteria has a place to live and food
– We are not helped or harmed in any way
Things That Affect Growth
Intermicrobial Relationships
• Synergism – two populations live
together and accomplish what neither
could alone
• Trench mouth – two populations of
bacteria (usually rods and spirochetes)
must be present for infection of the oral
cavity to occur
Things That Affect Growth
Intermicrobial Relationships
• Parasitism – symbiosis is beneficial to
one population (parasite) but harmful to
the other (host)
• The bacteria of all human diseases are
parasites
Applications
•
Industrial: Recover growth products
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•
Penicillin
Wine
Beer
Alcohol
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Vinegar
Pickles
Cheese
Medical: Phases of disease parallel
growth phases of pathogen