1. By Dr. Rakesh Prasad Sah
Assistant Professor
Microbial Growth & Metabolism
(Physiology of Bacteria)

2. Welcome To-------------

4. Coccus

5. Bacillus

6. Vibrio leptospira
Spirillum Mycoplasma

7. WHAT IS PHYSIOLOGY ?
 IT’S THE
 GROWTH,
 NUTRITION AND
 METABOLISM

9. Growth
 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
cells.
 Bacteria divide by binary fission.

10. ve
DS DNA Separation
of
Nuclear
strands
Formation of
new
complimentary
strands-2
identical DS
DNA
Transverse septum
formed
Septal mesosomes
involved
Septum
completed.
Cell wall
material
formed
Two daughter cells
formed. May
remain attached or
separate
BACTERIAL GROWTH & DIVISION
Bacteria divide by binary fission

11. Generation time
 Time required for division of bacterium into two cells in optimal
conditions.
 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
ceases/decreases
due to exhaustion of nutrients
and
accumulation of toxic products.

12. Generation Time Under Optimal Conditions
(at 37oC)
Organism Generation
Time
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
divisions)
Each bacterial colony
represents a clone of cells
derived from a single
parent cell.
 Turbidity – liquid media
-107-109 cells/ml

15. Bacterial counts
 Growth in numbers can be studied by bacterial
counts.
 2 methods – Total cell count
- Viable cell count

16. Total Count
 Total number of cells in the sample – living
+ dead.
 Can be obtained by :
1. Direct counting under microscope using
counting chambers.
2. Counting in an electronic device – Coulter
counter.

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
count.

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 :
 Lag,
 Log or Exponential
 Stationary &
 Phase of Decline.

20. Sep 07 Dr Ekta, Microbiology, GMCA

22. Phases of Growth Curve
Lag phase
Immidiately after inoculation –
no multiplication.
 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
exponentially.
 E.g. E. coli divides every 20 mins
1248163264 ……so
on…
 smaller cells, stain uniformly (Gram
stain)
 Best stage to perform biochemical
tests
 A straight line is obtained on graph
paper.

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
stationary
 irregular staining (Gram variable)
 sporulation and
 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
Temperature
Atmosphere – O2 & CO2
H-ion concentration (pH)
Moisture & drying
Osmotic effects
Radiation
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

27. Temperature
 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.

28. Effects of Temperature on Growth
95oF
77oF
40oF
Most of our plates are incubated at 37oC (98.6oF).

29. Temperature
 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

31. Atmosphere
 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
oxygen levels
e.g. Campylobacter spp, Helicobacter spp

32. Atmosphere
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.

34. H-ion Concentration
 pH range, optimum pH
 Neutral or slightly alkaline pH (7.2 – 7.6) –
majority of pathogenic bacteria grow best.
 Lactobacilli – acidic pH
 Vibrio cholerae – alkaline pH

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.
Radiation
 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
bacterial cells.
 Proteins, polysaccharides, lipids, nucleic acids,
mucopeptides & low molecular weight compounds make
up the remaining 20%.
 For growth & multiplication, the minimum nutritional
requirements are
 water
 source of carbon,
 source of nitrogen & some inorganic salts.

38. Classification of Bacteria Based on Nutritional
Requirement
Based on derive of energy
 Phototrophs – Bacteria which derive their energy from
sunlight.
 Chemotrophs – Bacteria which derive energy from
chemical reactions.
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
Nutritional Requirement
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
medical importance.
2. Heterotrophs – unable to synthesize their own
metabolites & depend on preformed organic
compounds.

40. Growth Factors
 Some bacteria require certain organic compounds in
minute quantities – Growth Factors OR Bacterial
Vitamins.
 It can be :
1. Essential – when growth does not occur in their
absence.
2. Accessory – when they enhance growth, without being
absolutely necessary for it.

41. Growth Factors
 Identical with mammalian nutrition
 Vitamin B complex –
1. Thiamine
2. Riboflavine
3. Nicotinic acid
4. Pyridoxine
5. Folic acid &
6. Vit.B 12

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…………………
MCQs

43. 1. Growth of bacteria is exponential in ………………………phase.
2. Growth of bacteria is in equilibrium state
in……………………phase.
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
…………….phase.

44.  Cold loving organisms are also called as…………….
 Most of the bacterial pathogens are
Mesophilic/psychrophilic/Thermophilic?
 Examples of Microaerophilic microorganisms are………&………
 Examples of Capnophilic microorganisms are……………&………