Module 1 Culture Media

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D R S H A R A D S H A R M A

Culture medium


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..

y culture medium is a liquid or geldesignedto supportthe growth of microorganisms , cells orsmallplants.

y culture media consist of nutrientsusedto grow microorganism orcells outside oftheir naturalhabitats.


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Basicrequirements ofculture media

y Energysource , (carbon source,nitrogen source)

y Mineralsalts ( sulphates phosphates andchloridesof K, Mg nd Ca )

y

pH - 7.2to 7.4y Accessory growth factors ( e.g , tryptophan for

salmonella typhi)


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Agar agar : most important constituents ofculture media

y Agar- agar: Itisused assolidifing agent ,

y containslong chain polysaccharides , inorganicsalt andproteins ,

y

solidify at42cy Melts at 98c

y Generally not metabolized by microbes,

y Obtained from sea weed (newzealand)


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Types ofculture media

Nutrient media

Minimal media

Selective mediaDifferential media

Enriched media

Transport media


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Nutrient media

source of amino acids and nitrogen is , beef yeast

orextract.

Undefined medium ( amino acidsourcecontains a

variety ofcompounds withtheexactcompositionbeing unknown)

Nutrient media contain alltheessentialelementsthat most bacteria need for growth and are non-selective, so they areused forthe general

cultivation and maintenance of bacteria keptin

laboratoryculturecollections.


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Nutrient media


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Minimal media

Containsthe minimum nutrientspossible forcolony growth, withoutthepresence of aminoacids.

Itis often used by microbiologists and geneticists

to grow wildtype microorganisms.Minimal medium typicallycontains:a carbon source (may be glucose or a lessenergy-

richsourcelikesuccinate)varioussalts, which mayvary among bacteria

species and growing conditions;these generallyprovideessentialelementssuch as magnesium,nitrogen, phosphorus, andsulfur to allowthe

bacteria to synthesizeprotein and nucleic acidwater


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Selective media

used forthe growth of onlyselect microorganisms.

(e.g, if a microorganism isresistantto a certainantibiotic, such as ampicillin ortetracycline, thenthat antibioticcan be addedto the medium inorderto prevent othercells, whichdo notpossesstheresistance, from growing).

Selective growth media are also usedin cellcultureto ensurethesurvival orproliferation ofcells with

certain properties, such as antibioticresistance orthe abilityto synthesize a certain metabolite.


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Selective media


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Someexamples ofselective media include:

y Eosin-methyleneblue agar (EMB) contains methyleneblue toxicto Gram-positive bacteria, allowing only growth ofGram negative bacteria

y Yeast and mold has a lowpH, deterring bacterial growth

y blood agar contains bovineheart bloodthat becomestransparentin thepresence ofhemolyticStreptococcus

y MacConkey agar forGram-negative bacteria

y Hektoen enteric agar (HE) whichisselective forGram-negative bacteria

y mannitol salt agar (MSA) whichisselective forGram-positivebacteria anddifferential for mannitol

y xylose lysinedesoxyscholate , isselective forGram-negativebacteria


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Differential media

Differential media or indicator media distinguish onemicroorganism type from another growing on thesame media.]

Thistype of media usesthe biochemicalcharacteristics of a microorganism growing in thepresence ofspecific nutrients orindicators (suchas neutralred, phenolred, eosin y, or methylene

blue).Examples ofdifferential media include:y eosin methyleneblue, whichisdifferential for

lactose andsucrose fermentationy MacConkey, whichisdifferential forlactose

fermentationy X-galplates, which aredifferential forlac operon

mutants


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Enriched media

Enriched media contain the nutrientsrequiredtosupportthe growth of a widevariety of organisms,including some ofthe more fastidious ones.

They arecommonlyusedto harvest as many

differenttypes of microbes as arepresentin thespecimen.

Blood agaris an enriched medium in whichnutritionallyrich whole bloodsupplementsthe

basic nutrients.

Chocolate agarisenriched withheat-treatedblood (40-45C), whichturns brown and givesthemedium thecolor for whichitis named.


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Transport media

y Transport media isused fortemporarystorage ofspecimens being transportedto thelaboratory forcultivation.

y maintainstheviability of all organismsin thespecimenwithout altering theirconcentration.

y contain only buffers andsalt.y lack ofcarbon, nitrogen, and organic growth factors

prevents microbial multiplication.y transport media usedin theisolation of anaerobes must

be free of molecular oxygen.

y

Example:Thioglycollatebroth forstrict anaerobes, Stuart

transport medium-a non-nutrientsoft agar gelcontaining a reducing agentto prevent oxidation,Venkat Ramakrishnan medium forv.cholerae


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Sterilization ofculture media

y Culture media aresterlized at:

y Temperature 121c,

y Pressure 15pascals,

y Time 15t020 minutes,y media containing heatsensitivesubstanceslike

serum , fatty acid ,sugars aresterlized by free

steam or filtration.


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Storage ofculture media

y Individual media isstoredin screwcapped bottles.

y Culture media ispreserved atlowtemperature (in

refrigeratirs orcoldrooms)

y Deep freezerefrigerators areused forpreservationof media containing antibiotics and amino acids ( -

10to -400c).


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Refrences

y MadiganM,Martinko J (editors). (2005).Brock Biology ofMicroorganisms (11th ed.). Prentice Hall. ISBN 0131443291.

y Birgit Hadeler,Sirkka Scholz, Ralf Reski (1995) Gelrite and agardifferently influence cytokinin-sensitivity ofa moss. Journal ofPlant Physiology 146, 369-371

y Ryan KJ, Ray CG (editors) (2004).Sherris Medical Microbiology(4th ed.).McGrawHill. ISBN 0838585299.y Cooper GM (2000). "Tools of Cell Biology".The cell: a molecular

approach. Washington, D.C:ASM Press. ISBN 0-87893-106-6.http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.section.128#148.

y

Washington JA(1996). "Principles of Diagnosis".Baron's MedicalMicrobiology (BaronSetal., eds.) (4thed.). Univ ofTexas MedicalBranch. ISBN 0-9631172-1-1.http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.5451#5457

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Module 1 Culture Media