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
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
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.
24.
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.
