bacterial growth & physiology

8/13/2019 Bacterial Growth & Physiology

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BACTERIAL GROWTH&PHYSIOLOGY

II MBBS

Dr Ekta Chourasia

Department of Microbiology


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Sep 07 Dr Ekta, Microbiology, GMCA

Growth

It is an increase in all the cell components,which ends in multiplication of cell leading toan increase in population.

It involves - an increase in the size of thecell & an increase in the number of individual

cells.

Bacteria divide by binary fission.


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Generation time

Interval of time between two cell divisions

OR

The time required for a bacterium to giverise to 2 daughter cells under optimumconditions

Also called population doubling time.


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Generation time

Coliform bacilli like E.coli& other medicallyimportant bacteria 20 mins

Tubercle bacilli 20 hrs

Lepra bacilli 20 days


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Growth form in Laboratory

Colonyformed by bacteria growing on solidmedia. (20-30 cell divisions)

Each bacterial colony represents a clone ofcells derived from a single parent cell.

Turbidityliquid media

- 107-109cells/ml

Biofilm formation thin spread over an inertsurface.


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Bacterial counts

Growth in numbers can be studied bybacterial 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 Coultercounter.


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Total Count

Can be obtained by :

3. Direct counting using stained smears - byspreading a known volume of culture over a

measured area of slide.

4. Opacity measurements using an

absorptiometer/ nephalometer.

5. Chemical assaysof cell components.


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Viable Cell Count

Measures the number of living cells.

Methods

Surface colony count1. Dilution method

2. Plating method

Number of colonies that develop afterincubation gives an estimate of the viablecount.


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Bacterial Growth Curve

When a bacterium is added to a suitableliquid medium & incubated, its growthfollows a definite course.

If bacteria counts are made at intervalsafter inoculation & plotted in relation totime, a growth curve is obtained.

Shows 4 phases : Lag, Log or Exponential,Stationary & phase of Decline.


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Phases of Growth Curve

Lag phaseNo increase in number but theremay be an increase in the size of the cell.

Log OR Exponential phase cells startdividing and their number increases

exponentially.


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Phases of Growth Curve

Stationary phasecell division stops due todepletion of nutrients & accumulation oftoxic products.- equilibrium exists between dying cells andthe newly formed cells, so viable countremains stationary

Phase of Decline population decreases dueto the death of cells autolytic enzymes.


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Morphological & Physiological

alterations during growth Lag phasemaximum cell size towards the end

of lag phase.

Log phasesmaller cells, stain uniformly

Stationary phaseirregular staining,sporulation and production of exotoxins &antibiotics

Phase of Decline

involution forms(with ageing)


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Factors Affecting Bacterial Growth

Temperature

Atmosphere O2 & CO2

H-ion concentrationMoisture & drying

Osmotic effects

RadiationMechanical & sonic stress.


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Temperature

Vary in their temperature requirements.

Temperature range

growth does notoccur above the maximum or below theminimum.

Optimum Temperaturegrowth occursbest, 37C for most pathogenic bacteria.


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Temperature

Mesophilicgrows best between 25C and40C.e.g. most bacterial pathogens

Psychrophilic(cold loving) grows best below20Ce.g. Flavobacterium spps

Thermophilicgrows best at high temp, 55-58Ce.g. Bacillus stereothermophilus


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Atmosphere

Depending on the O2requirement, bacteria aredivided into :1. Strict (Obligate) Aerobes require O2 for

growth e.g. Pseudomonas aeruginosa

2. Strict (Obligate) Anaerobes grow in theabsence of O2& may even die on exposure toO2 e.g. Bacteroides fragilis

3. Microaerophilicgrow best in the presence oflow oxygen levelse.g. Campylobacterspp, Helicobacterspp


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Atmosphere

4. Facultativeanaerobeaerobic but can alsogrow in the absence of O2e.g. Staphylococcus spps

5. Aerotolerant anaerobe anaerobic, buttolerates exposure to O2e.g. Clostridium perfringens

6. Capnophilic organism requires high CO2levels eg Neisseria spps


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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 choleraealkaline pH


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Moisture & Drying

Water essential ingredient of bacterialprotoplasm. Hence drying is lethal to cells.

Effect of drying varies :T.pallidumhighly sensitiveStaphylococcispstand for months

Spores resistant to dessication, maysurvive for several decades.


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Osmotic effects

More tolerant to osmotic variation due tomechanical 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 Nutrition

Water constitutes 80% of the total weightof bacterial cells.

Proteins, polysaccharides, lipids, nucleicacids, mucopeptides & low molecular weightcompounds make up the remaining 20%.

For growth & multiplication, the minimumnutritional requirements are water, asource of carbon, a source of nitrogen &some inorganic salts.


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Classification of Bacteria Based on

Nutritional Requirement PhototrophsBacteria which derive their

energy from sunlight.

Chemotrophs Bacteria which deriveenergy from chemical reactions.

1. Organotrophs: require organic sources ofhydrogen

2. Lithotrophs: require inorganic sources ofhydrogen like NH3, H2S


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Classification of Bacteria Based on

Nutritional Requirement Based on the utilization of carbon

compounds, bacteria are classified as :

1. Autotrophs can synthesise all theirorganic compounds by utilising atmosphericCO2& N2. No medical importance.

2. Heterotrophs unable to synthesise theirown metabolites & depend on preformedorganic compounds.


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Growth Factors

Some bacteria require certain organiccompounds in minute quantities Growth

Factors OR Bacterial Vitamins. It can be :

1. Essentialwhen growth does not occur intheir absence.

2. Accessory when they enhance growth,without being absolutely necessary for it.


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Growth Factors

Identical with mammalian nutrition

Vitamin B complex

1. thiamine2. riboflavine

3. nicotinic acid

4. pyridoxine5. folic acid &

6. Vit.B 12

bacterial growth & physiology

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