bacterial physiology ppt
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BACTERIAL PHYSIOLOGY
Deepa Babin
Asst Prof,Microbiology,TMC
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Welcome To-------------
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Meet the Microbes!
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Coccus
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Bacillus
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Vibrio leptospira
Spirillum Mycoplasma
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IT’S THE GROWTH, NUTRITION AND METABOLISM
WHAT IS PHYSIOLOGY ?
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Classification• Based on Nutrition bacteria are classified
as :1. Autotrophs – can synthesise all their
organic compounds by utilising atmospheric CO2 & N2. No medical importance.
2. Heterotrophs – unable to synthesise their own metabolites & depend on preformed organic compounds. All pathogens
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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
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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, a source of carbon, a source of nitrogen & some inorganic salts
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Based on Nutritional Requirement
• Phototrophs – Bacteria which derive their energy from sunlight.
• Chemotrophs – Bacteria which derive energy from chemical reactions.
• Organotrophs : require organic sources of hydrogen
• Lithotrophs : require inorganic sources of hydrogen like NH3, H2S
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OTHER GROWTH FACTORS• Identical with mammalian nutrition• Vitamin B complex – 1. thiamine2. riboflavine3. nicotinic acid4. pyridoxine 5. folic acid & 6. Vit.B 12
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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.
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Binary Fission
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Generation time• Interval of time between two cell
divisions OR • The time required for a bacterium to
give rise to 2 daughter cells under optimum conditions
• Also called population doubling time.
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GENERATION TIME
• Coliform bacilli like E.coli & other medically important bacteria – 20 mins
• Tubercle bacilli – 20 hrs
• Lepra bacilli – 20 days
Sep 07 Dr Ekta, Microbiology, GMCA
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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.
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OTHER FACTORS AFFECTING BACTERIAL GROWTH
TemperatureAtmosphere – O2 & CO2
H-ion concentrationMoisture & drying
Osmotic effectsRadiation
Mechanical & sonic stress
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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
• .
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CLASSIFICATION BASED ON TEMP• 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- 80ºC e.g. Bacillus sterothermophilus
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OXYGEN• 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. Bacteroides fragilis
3. Microaerophilic – grow best in the presence of low oxygen levels
e.g. Campylobacter spp, Helicobacter spp7
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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 perfringens6.Capnophilic organism – requires high
CO2 levels eg Neisseria spps
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The Effect of Oxygen (O2) on Growth
Needs oxygenGrows best in oxygen, but can grow without
Only grows without oxygen
Grows in low concentrations of oxygen
Grows with or without oxygen
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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
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Moisture and drying• Water – essential ingredient of bacterial
protoplasm. Hence drying is lethal to cells.
• Effect of drying varies : T.pallidum – highly sensitive Staphylococcus spp– stand for months• Spores – resistant to dessication, may
survive for several decades
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Sep 07
Osmotic effects
• More tolerant to osmotic variation due to mechanical strength of their cell walls.
Radiation • X rays & gamma rays exposure – lethal
Mechanical & Sonic Stress• May be ruptured by mechanical stress.
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BACTERIAL GROWTH CURVE• When a bacterium is added to a suitable liquid
medium & incubated, its growth follows a definite course.
• If bacterial 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.
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PHASES OF GROWTH
• Lag phase – No increase in number but there may be an increase in the size of the cell.
• Log or Exponential phase – cells start dividing and their number increases exponentially.
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Phases• 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
• Phase of Decline – population decreases due to the death of cells – autolytic enzymes.
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Morphological & Physiological alterations during growth
• Lag phase – maximum cell size towards the end of lag phase.
• Log phase – smaller cells, stain uniformly
• Stationary phase – irregular staining, sporulation and production of exotoxins
• Phase of Decline –involution forms(with ageing)
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BACTERIAL COUNTS• Growth in numbers can be
studied by bacterial counts.
• 2 methods – Total cell count - Viable cell count
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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.
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Viable Cell Count• Measures the number of living cells.• Methods – Surface colony count1. Dilution method2. Plating method• Number of colonies that develop after
incubation gives an estimate of the viable count.
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Metabolism• Absorption to Elimination of substances
in cells• Oxidation-Aerobes• Fermentation-Anaerobes• Oxidation-Reduction Potential (Redox
potential) - ELECTRONS TO ACCEPT OR TO PART WITH
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Biofilms• Microbial
communities• Form slime – quorum sensing
Biofilms form on teeth, contact lenses, & catheters
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THANK YOU