Bacterial Growth
BY
Dr. Nasir Garba Zango
DEPARTMENT OF MEDICAL MICROBIOLOGY
UNIVERSITY OF MAIDUGURI TEACHING HOSPITAL
19th May, 2026
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Introduction
• Growth is the organized increase in all structural and functional
components of a living organism.
• Enlargement caused solely by water uptake or storage of fat and
polysaccharides does not represent true growth.
• In bacteria, growth mainly occurs through binary fission, resulting in
cell multiplication.
• Repeated bacterial division increases the population size, forming
what is known as a culture.
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Introduction
• Bacteria multiply through binary fission, where a single parent cell
divides into two daughter cells.
• Each division cycle results in the production of two progeny cells
from one original cell.
• This repeated doubling process allows rapid expansion of bacterial
populations.
• Consequently, bacterial populations grow exponentially, also known
as logarithmic growth.
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Doubling time of bacteria
• The growth rate of bacteria is determined by the bacterial species,
nutrient composition of the medium, and environmental
temperature.
• Optimal growth occurs when bacteria are provided with suitable
nutrients and favorable conditions.
• Most pathogenic bacteria in nutrient-rich media double their mass
or cell number within 30–60 minutes.
• Variations in environmental and nutritional conditions can
significantly alter bacterial growth rates.
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Doubling time of bacteria
• Bacterial generation time varies widely, from about 20 minutes in
Escherichia coli to nearly 18 hours in Mycobacterium tuberculosis.
• Organisms with short doubling times can rapidly produce enormous
bacterial populations.
• A single E. coli cell may generate more than 1,000 progeny within 3
hours and over 1 million within 7 hours.
• Bacterial growth rates are influenced by species type, nutrient
availability, temperature, pH, and other environmental conditions.
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Doubling time of bacteria
• Psychrophiles grow optimally at low temperatures, including
refrigerator conditions.
• Thermophiles thrive at high temperatures, often exceeding 50°C.
• Mesophiles, which include most human pathogens, prefer
moderate temperature ranges.
• Some mesophiles can grow from refrigeration levels up to 42°C,
with optimal growth at 30–37°C.
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Growth cycle of bacteria
• Bacterial growth follows a characteristic cycle made up of four
distinct phases.
• When a small inoculum is introduced into liquid nutrient medium,
bacterial multiplication can be tracked over time.
• Regular counting of bacteria at intervals reveals predictable changes
in population size.
• These changes form the standard bacterial growth curve with four
main phases.
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Growth cycle of bacteria
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Growth cycle of bacteria
 Lag Phase
• The lag phase is a period of adaptation following transfer to a new
environment.
• Cells are initially metabolically depleted due to prior unfavorable
growth conditions.
• During this phase, essential enzymes and metabolic intermediates
are synthesized.
• Growth resumes once these components accumulate to sufficient
levels.
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Growth cycle of bacteria
 Exponential Phase
• During the exponential phase, bacterial cells are in a steady
metabolic state with constant biosynthesis.
• Cell mass increases exponentially because
components also support further growth.
newly
formed
• Growth continues until nutrients are depleted or toxic by-products
accumulate and inhibit replication.
• In aerobic cultures, oxygen becomes limiting at high densities,
slowing growth despite aeration and agitation.
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Growth cycle of bacteria
 Stationary Phase
• Growth eventually stops due to nutrient depletion or buildup of
toxic metabolic by-products.
• In the stationary phase, bacterial populations often experience
simultaneous cell death and new cell formation.
• This balance results in minimal net change in viable cell numbers.
• Total cell counts may rise slightly, even though overall viable counts
remain stable.
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Growth cycle of bacteria
 Death Phase
• Growth eventually stops due to nutrient depletion or buildup of
toxic metabolic by-products.
• In the stationary phase, bacterial populations often experience
simultaneous cell death and new cell formation.
• This balance results in minimal net change in viable cell numbers.
• Total cell counts may rise slightly, even though overall viable counts
remain stable.
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Phases of the Microbial Growth Curve
Phase
Growth Rate
Lag
Zero
Exponential
Constant
Maximum stationary
Zero
Decline
Negative (death)
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Thank you
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