It is an increase in all the cell components,
which ends in multiplication of cell leading to
an increase in population.
It involves - an increase in the size of the
cell & an increase in the number of individual
Bacteria divide by binary fission.
DS DNA Separation
Two daughter cells
remain attached or
BACTERIAL GROWTH & DIVISION
Bacteria divide by binary fission
11. Generation time
Time required for division of bacterium into two cells in optimal
Ordinary bacterium doubles every 20-30 mins, and their number
increases by geometric progression. Theoretically a single bacterium
form 10²¹ cells in 24 hrs.
But in culture medium (batch culture) cell division
due to exhaustion of nutrients
accumulation of toxic products.
12. Generation Time Under Optimal Conditions
Bacillus cereus 28 min
Escherichia coli 20 min
Staphylococcus aureus (causes many types of infections) 27-30 min
Mycobacterium tuberculosis (agent of Tuberculosis) 20 hrs
Mycobacterium lepra 20 days
Treponema pallidum (agent of Syphilis) 30 hrs
13. Growth form in Laboratory
Colony – formed by
bacteria growing on solid
media. (20-30 cell
Each bacterial colony
represents a clone of cells
derived from a single
Turbidity – liquid media
16. Total Count
Total number of cells in the sample – living
Can be obtained by :
1. Direct counting under microscope using
2. Counting in an electronic device – Coulter
17. Viable Cell Count
Measures the number of living cells.
Methods – Surface colony count
1. Dilution method
2. Plating method
Number of colonies that develop after
incubation gives an estimate of the viable
19. Bacterial Growth Curve
When a bacterium is added to a suitable medium &
incubated, its growth follows a definite course.
If bacteria counts are made at intervals after
inoculation & plotted in relation to time, a growth
curve is obtained.
Shows 4 phases :
Log or Exponential
Phase of Decline.
22. Phases of Growth Curve
Immidiately after inoculation –
Adapt to new environment.
Increase in size due to accumulation
of enzymes and metabolites.
maximum cell size towards the end
of lag phase.
Reach the stage of multiplication
Period between inoculation and beginning of multiplication is
known as lag phase.
Duration depends on—species, size of inoculation, nature of
culture medium, environmental factors.
23. Phases of Growth Curve
Log OR Exponential phase –
Cell division starts and bacteria
increases their number
E.g. E. coli divides every 20 mins
smaller cells, stain uniformly (Gram
Best stage to perform biochemical
A straight line is obtained on graph
24. Phases of Growth Curve
Stationary phase –
cell division stops due to
depletion of nutrients &
accumulation of toxic products.
equilibrium exists between dying
cells and the newly formed cells,
so viable count remains
irregular staining (Gram variable)
production of exotoxins ,
antibiotics & bacteriocins
25. Phase of Decline
Viable cell count decreases
Bacterial division ceases
Exhaustion of nutrients
Accumulation of toxic products
Cell death by autolytic enzymes
Total count pararrels viable count
upto end of stationary phase. After
this, viable count decreases.
Total count remains same, later
decreases due to autolysis of cells.
Phases of Growth Curve
26. Factors Influencing Microbial Growth
Atmosphere – O2 & CO2
H-ion concentration (pH)
Moisture & drying
Mechanical & sonic stress.
This scanning electron micrograph (SEM) depicts
numerous clumps of methicillin-resistant Staphylococcus
aureus bacteria, commonly referred to by the acronym,
MRSA, by Janice Haney Carr, PHIL #10046
Vary in their temperature requirements.
Temperature range – growth does not occur
above the maximum or below the minimum.
Optimum Temperature – growth occurs best,
37ºC for most pathogenic bacteria.
Mesophilic – grows best between 25ºC and 40ºC.
e.g. most bacterial pathogens
Psychrophilic (cold loving) – grows best below 20ºC
e.g. Flavobacterium spps
Thermophilic – grows best at high temp, 55- 58ºC
e.g. Bacillus stereothermophilus
Depending on the O2 requirement, bacteria are
divided into :
1. Strict (Obligate) Aerobes – require O2 for
growth e.g. Pseudomonas aeruginosa
2. Strict (Obligate) Anaerobes – grow in the
absence of O2 & may even die on exposure to O2
e.g. Clostridium tetani.
3. Microaerophilic – grow best in the presence of low
e.g. Campylobacter spp, Helicobacter spp
4. Facultative anaerobe – aerobic but can
also grow in the absence of O2
e.g. Staphylococcus spps
5. Aerotolerant anaerobe – anaerobic, but
tolerates exposure to O2
e.g. Clostridium perfringens
6. Capnophilic organism – requires high CO2
levels eg Neisseria spps, Brucella abortus.
35. Moisture & Drying
Water – essential ingredient of bacterial
protoplasm. Hence drying is lethal to cells.
Effect of drying varies :
T.pallidum – highly sensitive
Staphylococci sp– stand for months
Spores – resistant to dessication, may survive
for several decades.
36. Osmotic effects
More tolerant to osmotic variation due to
mechanical strength of their cell walls.
Plasmolysis – hypertonic sol - shrinkage
Plasmoptysis – from hypotonic sol – D.W. – swelling &
rupture of the cell.
X rays & gamma rays exposure – lethal
Mechanical & Sonic Stress
May be ruptured by mechanical stress. (vigrous
shaking and by exposure to ultrasonic vibration)
37. Bacterial Nutrition
Water constitutes 80% of the total weight of
Proteins, polysaccharides, lipids, nucleic acids,
mucopeptides & low molecular weight compounds make
up the remaining 20%.
For growth & multiplication, the minimum nutritional
source of carbon,
source of nitrogen & some inorganic salts.
38. Classification of Bacteria Based on Nutritional
Based on derive of energy
Phototrophs – Bacteria which derive their energy from
Chemotrophs – Bacteria which derive energy from
Based on source of Hydrogen
1. Organotrophs : require organic sources of hydrogen
2. Lithotrophs : require inorganic sources of hydrogen
like NH3, H2S
39. Classification of Bacteria Based on
Based on the utilization of carbon compounds,
bacteria are classified as :
1. Autotrophs – can synthesize all their organic
compounds by utilizing atmospheric CO2 & N2. No
2. Heterotrophs – unable to synthesize their own
metabolites & depend on preformed organic
40. Growth Factors
Some bacteria require certain organic compounds in
minute quantities – Growth Factors OR Bacterial
It can be :
1. Essential – when growth does not occur in their
2. Accessory – when they enhance growth, without being
absolutely necessary for it.
42. 1. Bacteria divides by…………………..
2. Generation time of E. coli is…………………
3. Generation time of Mycobacterium tuberculosis is…………..
4. Generation time of Mycobacterium leprae is…………..
5. The time period between inoculation and beginning of
multiplication is called…………………
43. 1. Growth of bacteria is exponential in ………………………phase.
2. Growth of bacteria is in equilibrium state
3. Viable count is decreases in …………………..phase.
4. Complete exhaustion of nutrients and accumulation of toxic
products occurs in ……………..phase.
5. Best time to perform Gram staining and biochemical tests in
44. Cold loving organisms are also called as…………….
Most of the bacterial pathogens are
Examples of Microaerophilic microorganisms are………&………
Examples of Capnophilic microorganisms are……………&………