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Microbial Growth
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Bacterial cell is composed of : •
Water •
Organic •
Protein •
Sugars •
Lipids •
Nucleic acid •
Microbial nutrition
Macronutrients – required in large quantities; •
play principal roles in cell structure &
metabolism
proteins, carbohydrates –
Micronutrients or trace elements – required •
in small amounts; involved in enzyme function
& maintenance of protein structure
manganese, zinc, nickel –
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Bacterial Nutrition and Growth
Classification based on their source of
carbon
1. Autotrophs •
2. Heterotrophs :saprophytes ; parasites
•
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Bacterial Nutrional Modes
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Requirements for Microbial
Growth
Physical Requirements •
Chemical Requirements •
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The Requirements for Growth
The requirements for microbial growth can be •
divided into two main categories:
physical and chemical.
Physical aspects include
temperature, pH, and osmotic pressure. •
Chemical requirements
include sources of carbon, nitrogen, sulfur, •
phosphorus, oxygen, trace elements, and
organic growth factors.
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Temperature •
Optimum temperature – promotes the fastest rate of
growth and metabolism
•
Mesophilic forms （30-37C ℃）include all human
pathogens and opportunists.
•
pH •
• Many grow best at neutral pH (Most bacteria grow in
the range of pH 6.5-7.5
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Requirements for Microbial Growth
Physical requirements
The composition of bacterial cell is 80-90%
water.
3- Osmotic Pressure
In high osmotic pressures solution
(hypertonic), the water move from inside
bacterial cell to outside
The growth of the cell is inhibited as the plasma •
membrane pulls away from the cell wall.
Thus, addition of salts or other solutes to solution can
be used to preserve food.
Loss of water from the cell results in Plasmolysis. •
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Oxygen Requirements
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for growth Required CO2
N. meningitidis •
N. Gonorrhoeae
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Requirements for Microbial Growth
chemical requirements
# Carbon:
Chemoheterotrophs: organic matter •
Chemooutotrophs , photoutotrophs •
from Co2.
# Nitrogen _Sulfur _and phosphorous
# Trace Elements: iron
_ copper _ and zinc
# Oxygen:
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Bacterial growth •
&•
reproduction •
Binary fission in bacteria
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Bacterial culture •
Culture media
Any material prepared in the laboratory for •
the growth of bacteria and usually in test
tubes or petri dishes
Culture = microbes that grow & multiply in •
or on a culture medium
Culture Media
Culture medium
Inoculum
Culture
Sterile
Types of culture media
Solid (agar)/semisolid/liquid
(broth)
Agar;
liquid down to 50C
solidify at 45 C, not
consumed by bacteria as
nutrient.
Agar solid media are poured
in plates(Petri dish) or tubes.
In tubes they are poured
either as slants or deeps.
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Culture media
Chemically defined media = is one in •
which the exact chemical composition is
known (energy source , carbon , nitrogen ,
sulfur , phosphorus , growth factors)
Complex media = in which the exact •
chemical composition varies slightly from
batch to batch (protein added)
Culture media
Differential media = •
used to distinguish
among different
kinds of bacteria
Culture media
Selective media = •
allow the growth of
only one kind of
bacteria & prevent
the growth of other
by the addition f
certain salts &
dyes
Culture media
Enrichment •
media = is used
to encourage the
growth of
particular
bacteria in mixed
culture
Obtaining pure culture •
Streak-Plate Method
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Inoculated culture media must be •
incubated at 37C = incubator
*some bacteria require an increased •
CO2 concentration = CO2 incubator or
candle jars can be used
*some bacteria need anaerobic condition •
to grow ( remove O2)
Bacterial colonies on several differential media.
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The Growth of Bacterial Cultures
Binary fission •
Generation time •
Phases of Growth •
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Growth curve
Lag phase – “flat” period of adjustment, enlargement;
little growth
Exponential growth phase – a period of maximum
growth will continue as long as cells have adequate
nutrients & a favorable environment
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Stationary phase – rate of cell growth equals rate of cell
death cause by depleted nutrients & O2, excretion of
organic acids & pollutants
Death phase – as limiting factors intensify, cells die
exponentially in their own wastes
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Generation time
time for bacterial mass to double •
Example •
100 bacteria present at time 0
If generation time is 2 hr
After 8 hr mass = 100 x 24
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Obtaining Pure Culture
Colony=is a visible mass of microbial cell •
that theoretically arose from one cell
Streak plate technique •
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The streak plate method for isolating pure bacterial
cultures.
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First Term Exam.
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