The document discusses bacterial physiology, including nutrition, environmental factors affecting bacterial growth, and metabolism. It provides details on: - The optimal nutritional requirements for bacterial growth, including water, sources of carbon and nitrogen, inorganic salts, and growth factors. - How environmental factors like temperature, pH, oxygen levels, moisture, and stressors affect whether bacteria can survive. - The stages of bacterial growth (lag phase, log phase, stationary phase, and declining phase) and how growth is measured over time in a bacterial growth curve. - That bacteria undergo aerobic respiration or fermentation depending on the availability of oxygen, and how both pathways generate energy in the form of ATP.

1. Lecture 4

2. Bacterial
physiology
Nutrition
Environmental
factorsaffecting
survival of
bacteria.
Growth &
multiplication
Metabolism

3.  Nutrition-
 It is a process by which, chemical substances called as
nutrients, are obtained from surrounding environment
& used for metabolicactivityand growthof thecell.
 Most of medically imp bacteria grow on simple media
with one source of organicmaterial.
 Some bacteria requires more complexmedia
containing certain organic compounds k/a “fastidious
bacteria”.

4.  Optimum nutritional requirements for
growth of bacteria.
 Water
 Source of carbon
 Source of nitrogen
 Inorganicsalts
 Growth factors
 Source of energy

5. Water-
 Most imp requirement as it constitute 80% of total weight.
 Vehicle for entry of the nutrients into the cell.
 Elimination of all wasteproducts.
 Participates in metabolicreaction.
 Is an integral part ofprotoplasm.

6. Source of carbon & energy-
Bacteria are divided into 2groups
Autotrophic/Lithotrophic- Can use CO2 as a sole
source of carbon for synthesis of all their organic
metabolites
 They require water, inorganic salts & CO2 forgrowth &
derive energy eitherfrom
 Light (photolithotrophic) or
 Chemical reaction(chemolithotrophic)
 Areconcerned with soil fertility & are medically less
important .e.g. nitrogen fixing bacteria insoil

7. Heterotrophic/Organotrophic bacteria-
 Unable to use CO2 as a sole source of carbon.
 Require it in various organic form e.g. glucose,
amino acids, nucleotides, lipids.

8. Source of nitrogen-
 N2 atom of important biomolecules (like amino
acids,purines, pyrimidines) comes from NH4ions.
 It may comesfrom
a) Assimilatory nitrateproduction
b) Dissimilatory nitratereduction
Certain species are able to fix atmospheric N2 into usable
organic form.e.g.azatobactor, blue green algae, kleb.
pneumoniae

9. Inorganic salts
 Theseare required forosmoticregulation
 Areessential forcertain enzymesystems.
 The anions- phosphate &sulphate
 The cations- sodium, potassium, magnesium, iron,
calcium, manganese.

10. Growth factors-
 Many pathogenic species requires certainkey
substances for their growth k/a ‘growth factors’ or
‘bacterial vitamins’.
 Includes B complex vitamins, purines, pyrimidines,
aminoacids
 They are provided by various body fluids & tissues ‘in
vivo’ and in the form of yeast extract , blood &blood
products ‘invitro’.

11. • Moisture & dessication
• CO2
• O2 requirement
• Temperature
• p H
• Light
• Osmotic effect
• Mechanical & sonicstress
Environmental
factors affecting
growth of
bacteria

12.  Moisture & dessication-
 Moisture isan absolute requirment forgrowth.
 Therefore drying is lethal tocells.
 Treponema & gonococci are sensitive todrying.
 Staphylococci can withstand drying formonths.
 CO2-
 It is obtained either from environment or produced
endogeneously
 A few bacteria require additional CO2(5-10%) for their
growth e.g. Brucella abortus, Neisseria,pneumococci.
 These are k/a Capnophilicbacteria.

13. O2 requirement-
CLASS DEFINITION EXAMPLE
Obligate
aerobe
Grows only in
presence of O2
Mycobacterium
tuberculosis
Obligate
anaerobe
Grows only inabsence
of O2
Clostrodia
Facultative
anaerobes
Are generally aerobes,
but can also grow in
absence of O2
Most bacteria
of medical
importance
Microaerop
hilic
bacteria
Grows under lowO2
tension
Campylobactor

14. In obligate aerobes and facultative anaerobes:
Superoxide dismutase enzyme degrades superoxide anion.
Catalase and peroxidase enzymes degrade hydrogen peroxide.
BUT
In obligate anaerobes:
These enzymesare not present.
So, thepresenceof oxygen is toxic to them.
In the presence of oxygen, two toxic substances to the bacteria
are produced which are hydrogen peroxide and superoxide anion.

15. Temperature-
 Pathogenic bacteriagrows bestat body temp.i.e.37 c
 Thermal death point- Lowest temp that kills a
bacterium under standard condition in a given time.
 Mesophilic bacteria having thermal death point50-65
 Spores have thermal death point between 100-120C.
Bacteria type Temperature Example
Psychrophillic 0-20 Soil & water
saprophytes
Mesophilic 25- 40 Majority of
pathogenic bacteria
Thermophilic 55-80 Bacillus & Clostrodia

16. pH-
 Most bacteriagrows bestatoptimum p H of 7.2-7.6
 Growth is poor below p H 6.0 & above 7.8
 Growth stops below p H 5.0 & above9.0
 Lactobacillus species grows at acidic p H & k/a
acidophiles
 Vibrios are sensitive toacid but toleratealkali.

17. Light-
• Bacteria grows well indark
• Theyaresensitive to UV rays & otherradiation.
• Photosysnthetic bacteria require light for
photosynthesis.
• Photochromogenic bacteria produce pigment only
when exposed tolight.

18. • Osmoticeffect-
• Sudden exposure to hypertonic solution
causes osmotic withdrawl of water &
shrinkage of the cell k/aPlasmolysis.
• Sudden transfer from concentrated solution to
distilled water causes imbibition & rupture of
cell & is k/ aplasmoptysis.
• Mechanical & sonicstress-
• Cell wall may be rupured by grinding &
vigorous shaking.
• It may be disintegrated by exposure to
ultrasonic vibration.

19.  Growth & Multiplication of
bacteria
Bacterial growth means balanced increase incell mass in
termsof-
a) Increase in size OR
b) Increase in number ofcells
 When growth reaches critical mass, celldivides
Bacteria may reproduce by binary fission
In binary fission nuclear division precedescell division.

20. Bacteria showing binary fission
Cell divides by constrictive orpinching by ingrowth
of septum across cellwall

21. Generation time-
Time required for bacterium to give rise to 2 daughter
cells under optimum condition is k/a ‘generation time’
or ‘population doubling time’.e.g.
Coliform bacteria 20 min
Tubercular bacilli 20 hrs
Lepra bacilli 20 days

22. Bacterial counts
 Total count- gives total number of cells irrespectiveof
whethertheyare living ordead.
 Viable count- gives total number of living cellsonly.
 Total count can be obtainedby
 Direct counting undermicroscope
 Counting in ‘Coulterchamber’.
 By ‘Absorptiometer’ or‘Nephalometer’.
 By chemical assay withN2
 Using theirwetordry weight
 Viable count can be obtained by dilution &plating
method

23. Bacterial growth curve-
 When bacterium is seeded into a suitable liquid
medium & incubated, its growth follows a definitive
curve & is k/a ‘ bacterial growthcurve’.
 In this graph bacterial count is determined at different
intervals & plotted in relation withtime.

25. Lag phase-
 No appreciable increase in number but there may be
increase in size. Maxcell size is obtained.
 This is time required for adaptation to new
environment.
 Enzymes & metabolic intermediates are builtup.
 Lasts for 1-4 hrs & its duration varieswith species,
nature of medium,temperature.
 Clinical significance- incubation period of disease
Log phase-
 Cells starts dividing & their number increases
exponentially withtime.
 Cells are smaller & stainuniformly.

26.  No.of newly formed cells >no. of cellsdying
 Clinical significance- symptoms & signsappears.
Stationaryphase-
 Growth rateslows d/tdepletion of nutrients &
accumulation of toxicproducts.
 No. of newly formed cells=no. of cellsdying
 Cellsaregramvariable & shows irregularstaining d/t
presence of storagegranules.
 Sporulationoccurs.
 Declining phase-
 More nutritional exhaustion & toxinaccumulation.
 Death of cells d/t autolyticenzymes.
 Clinical significance- phase of convalescence.

27.  Bacterial metabolism-
Absorbed food( carbohydrates, fats, proteins) are
utilized & eliminated by certain metabolicpathways.
Aerobic bacteriaobtain theirenergy byoxidation
involving O2 as a ultimatehydrogen acceptor.
In anaerobic bacteria, hydrogen acceptor is other than
O2.
Facultative bacteria can utilize bothpathways.

28.  Oxidation-
 Ultimate electron acceptor isO2
 Carbon & energy sourceare broken down into CO2 &
H2O
 Energy is generated by oxidativephosphorylation,
i.e productionof energy rich phosphate bonds & their
transfer to ADP to formATP

29.  Fermentation
 In anaerobic bacteria, growth occurs by process in
which carbon & energy sourceactsas both- electron
donor & acceptor in a series of oxidoreduction k/a
fermentation.
 e- acceptors are nitrates &sulphites.
 Following products areformed
 Acids -lactic acid, formic acid, Pyruvicacid
 Alcohols
 Gases – H2, CO2

30. Substrate level phosphorylation-
• During fermentationenergy rich phosphate bondsare
produced by introduction of organic phosphate into
intermediate metabolites k/a substrate level
phosphorylation.
• These phosphates bondsare transferred toADP to
form ATP.

31.  Redox potential (Eh)-
 Oxidising orreducing condition of system is indicated
by the net readiness of all components in a system to
take upor loseelectrons. k/a “redox potential(Eh)”.
 Measured in mV.
 Best estimated by measuring potential diffbetween
medium & electrode immersed init.
 More oxidised the system, more isthe Eh.
 Methylene bluecan detectchange in Eh.

32. THANK YOU!