Definition of bacterial growth Modes of multiplication in bacteria List the salient features of bacterial growth curve. Concepts of generation time and growth curve Calculations of generation time  

1. Growth of bacteria
Mrs. V. A. Warad
Assistant Professor
Pharmaceutical Microbiology
PES, Modern College of Pharmacy, (for Ladies), Moshi, Pune
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2. Objectives
1. Definition of bacterial growth
2. Modes of multiplication in bacteria
3. List the salient features of bacterial growth
curve.
4. Concepts of generation time and growth
curve
5. Calculations of generation time
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3. Definition of growth in bacteria
Bacterial size – very small
Growth can not be defined or observed
as increase in size or mass
Hence growth in bacteria is defined as
increase in number of bacterial cells.
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4. Modes of reproduction in bacteria
Bacteria reproduce mainly by asexual methods.
1. Binary fission –
Major mode of reproduction in bacteria
One bacterial cell divides into two equal cells
Ex. - B. subtilis, S. aureus
Other modes are less common, observed in few bacteria
2. Budding – Rhodopseudomonas acidophila
3. Fragmentation – Nocardia
4. Spore formation – Streptomycetes
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5. Sexual methods of reproduction in bacteria
Rarely bacteria reproduced by sexual
methods.
Sexual methods are:
1. Transformation
2. Transduction
3. Conjugation
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6. Generation time
It is time required for bacterial cell to divide.
It depends on bacterial species, nutrients and
incubation conditions.
Bacterium Generation time (min)
E. coli in broth 17
E. coli in milk 12
S. aureus 27-30
Mycobacterium tuberculosis 792-932
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7. Calculations of generation time
Bacteria multiply by binary fission and bacterial population
increases exponentially
1 → 2→ 22→ 23 → 24 →→→ 2n
N = 1 x 2n
Where
n = No. of generation
N= Final population
N₀= initial population
N = N₀ x 2n
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8. Calculations of generation of time
Log N = log N₀ + n log 2
n = log N – log N₀ / log 2
n = log N – log N₀ / 0.3010
n = 3.3(log N – log N₀)
g = t /n
g = t /3.3 (log N – log N₀)
Growth rate: No. of generations of bacteria per hour
Growth rate = 1/g
= 3.3(log N – log N₀) /tMicrobiology/Bacterial growth/VAW
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9. Puzzle
E. coli cells take 2 hrs. produce 1024 cells. How
much time they will take to produce 2048 cells?
(Generation time of E.coli is 20 min)
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10. Puzzle
Generation time of Pseudomonas aeruginosa
is 30 min. calculate its growth rate?
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11. Growth curve of bacteria
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Bacterial inoculum is added to nutrient medium
and incubated.
Samples from medium are removed immediately
and every hour for 48hrs.
Number of viable cells are counted every hour
and growth curve is plotted.
Definition: It is a graph of log of number of
viable bacterial cells verses time in hours

12. Growth curve of bacteria
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13. Different phases of growth curve
1. Lag phase
2. Logarithmic / Exponential growth phase
3. Stationary growth phase
4. Logarithmic / Exponential death phase
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14. 1. Lag phase
There is no increase in number of cells.
It is time taken by cells to adjust with new
environment.
Synthesis of proteins, enzymes, coenzymes
occurs.
Cells enlarge in size.
Cells start dividing at the end of lag period.
All cells do not divide at same time.
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15. There is gradual increase in number.
And there is gradual increase in growth rate
Duration of lag phase depends on state of
organisms used for inoculation. Lag phase is
long when inoculum is obtained from old
culture. Lag phase is short if inoculum is
obtained from young culture / from log phase.
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16. 2) Logarithmic growth phase
Cell population increases exponentially.
Generation time is constant and shortest.
Growth rate is constant and highest.
Cell population is uniform with respect to chemical
composition, metabolic activities, relative concentrations of
metabolites.
Cell population is metabolically very active.
Cells size is small.
Cells are sensitive to physical and chemical agents.
It lasts for few hours.Microbiology/Bacterial growth/VAW
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17. 3) Maximum stationary phase
There is further decrease in nutrient level and
accumulation of metabolic waste
There is no net increase in number of bacteria.
Growth Rate and death rate are equal.(no. of cells
newly formed = no. of cells dying)
Cells are resistant to physical and chemical
agents.
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18. Exponential death phase
Death rate is more than growth rate.
Bacteria die faster than new cells are
produced.
Number of viable cells decrease
exponentially.
Cell population becomes half in same time
interval.
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19. At the end of exponential death phase very
few viable cell remain in culture and survive
for few days.
For most of the bacteria this phase lasts for
3-4 days.
In case of endospore producing bacteria it
may last for few months.
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