Culture Media

-


¢ Culture media
Media which are designed to provide all the essential nutrients in solution for bacterial growth
—  nutrients or nutritional requirements- chemicals and elements of the environment that are utilized for bacterial growth
¢ Culture bacteria- why?
—  For their identification
—  Cannot be recognised by their morphology alone
—  Have to be isolated on culture media and obtained as pure cultures for study
¢ Types
¢ Classified in many ways
¢ According to physical state
—  Solid media , liquid media and semisolid media
¢ According to nutritional factors
—  Simple media and complex media, synthetic media , semidefined media and special media
¢ According to use for different organisms
—  Aerobic and anaerobic media
¢ History
¢ Original media
—  Louis Pasteur:  urine and meat broth
¢ Solid media 
—  by Robert Koch: cooked potato
—  Gelatin to solidify liquid media ( by Koch) but no useful because liquefied at 24OC and by many proteolytic bacteria
¢ Frau hesse (wife of one of the investigator in Koch’s laboratory)- used agar to solidify culture media
¢ Constituents of basal culture media
¢ Water
—  sources of hydrogen and oxygen, low mineral content preferable
—  Copper distilled water should not be used
¢ Electrolyte
—  sodium chloride or other elctrolytes
¢ Peptone
—  complex mixture of partially digested protein
—  Contains water soluble products eg pepsin, trypsin or papain
—  should  allow the growth of moderately exacting bacteria, absence of fermentable carbohydrate, low content of copper
¢ Meat extract, yeast extract: contain protein degradation products, carboydrates, inorganic salt and certain growth factors
¢ Agar
—  used for preparing solid media.
—   obtained from seaweeds
—   chief constituent is long chain polysaccharide(complex polysaccharide)
—  Also contain inorganic salts and ,small amount of protein like material and some traces of long chain fatty acid.
—  Virtually no nutritive value and is not affected by the growth of bacteria
—  Melts at 95 OC and solidifies at 42 OC
—  Hydrolysed by high alkaline and acidic pH
¢ Act as solidifying agent of culture media
¢ Different types of agar eg. New Zealand agar and Japanese agar( jellifying property different)
¢ Manufactured either as dried fibres or as powder
      Nutrient agar
                             
  Nutrient broth
¢ Simple media( basal media)
¢ Simplest media used commonly in diagnostic laboratories
¢ Nutrient broth (liquid) , nutrient agar(solid), peptone water
¢ Peptone water -– 1% peptone, 0.5 %  sodium chloride and  distilled water and pH  (7.4-7.5)
¢ Nutrient broth  – 1% peptone, 0.5 %  sodium chloride and  distilled water and pH (7.4-7.5) + 1% meat extract
                                     Liquid media
¢ Nutrient agar- nutrient broth + 2%agar
¢ 0.2-0.5 % of agar –semi solid agar- used for motile organisms to spread.
¢ 6% agar prevent spreading or swarming by organisms like Proteus.
¢ Complex media
¢ Have added ingredients  for special purposes or for bringing out certain characteristics or providing special nutrients required for the growth of the bacterium under study
1) general purpose medium- eg. Blood agar
     capable of detecting most aerobic and facultatively anaerobic organisms
       Commonly used for the general isolation of microorganisms directly from primary specimens inoculated in the agar
¢ 2) Enriched media – substances like blood, serum or eggs are added
—   media that allow growth of fastidious organisms ( presence of haemin, cystein)
—  eg,. Blood agar chocholate agar, loeffler’s serum
media
Chocolate Agar
¢ 3) enrichment media – liquid medium

—  Favours the growth of particular species of bacteria
—  Substances having stimulating effect
—  e.g.  Selenite broth, tetrathinate broth, alkaline peptone water and Robertson’s cooked meat medium
¢ Blood agar
¢ Chocolate agar
¢ 4) Selective media – contain additives that enhance the growth of the desired organisms and inhibit other organisms
—  Solid media
—  Use to isolate particular bacteria from mixed infection
—  e.g bile salt agar, Thiosulphate citrate bile salt sucrose (TCBS) : only vibrio grow
—  deoxycholate citrate agar, MacConkey’s agar, lowenstein jensen medium etc
¢ TCBS
¢ 5) Indicator media
—  Certain indicator is incorporated in media
—  eg neutral red , bromothymol blue, potassium tellurite
¢ 6) Differential medium- contains substances which help to distinguish differing properties of bacteria
—  eg MacConkey agar( also an indicator media and selective media), blood agar
¢ MacConkey agar
¢ Composition
—  Peptone, agar , lactose, sodium taurocholate and neutral red
—  Transport media
—  Those bacteria who may not survive for long time
—  Or may be overgrown by another nonpathogenic bacteria
—  eg: Stuart’s transport media
—  Bile peptone transport medium for stool (vibrios )
—  Glycerolsaline transport medium for stool( dysentery bacilli)
¢ Transport media
¢ Brain heart infusion (BHI) broth
¢ Contd….
Biphasic media:
 Castaneda medium – for Brucella
-        Two phases; solid and liquid
¢ Biochemical media
¢ Routinely used:
  - Triple Sugar Iron (TSI) agar
  - Citrate medium
  - Urease medium
  - Sulphide Indole Motility (SIM) medium* semisolid  medium
     
                            
¢ Sugar media-( fermentation substances)
¢ For biochemical tests
¢ Contains
¢ 1%sugar concerned in peptone water
¢ Anrades indicator
¢ Durham’s fermentation tube is also kept
¢ Detection –acid production by colour change and gas production by accumulation gas in the tube
¢ Glucose , sucrose lactose and mannitol are generally used for sugar fermentation tests
Mycobacterial culture media
¢ Eg Lowenstein-Jensen media, middlebrook or  based media
¢ Mycobacteria need special media
Anaerobic media
¢ eg –Robertson’s cooked meat media, thiglycolate broth etc
¢ Media used to grow anaerobic organism
¢ Nutritionally enriched
¢ Prereduced of molecular oxygen for better growth of anaerobes
                          

Comments

Post a Comment

Popular posts from this blog

Separating Medium

-
Definition Separating media are those substances which is used to separate two surfaces from each other. Separating media help to separate A.             Plaster surface to acrylic surface B.             Plaster surface to plaster surface C.            Plaster surface to metal surface D.            Plaster surface to impression material surface Classification 1. Oily and greasy substances a) Vaseline b) Liquid paraffin c) Grease in crude form d) Mineral and vegetable oil These substances when applied, absorbs onto the plaster surface and thus aids in separation Disadvantage §   They weaken the plaster surface §   Cannot be uniformly and evenly applied on the plaster surface §   Details of impression cannot be copied precise...
Read more

Chemical Stages of Polymerization of Acrylic Resin

-
DENTURE BASE MATERIALS DENTURE BASE MATERIALS VULCANITE (1855)– Rubber with 32 % Sulphur & Metallic oxides.   Advantages – It is nono-toxic, non-irritant, has excellent Mechanical properties   material is sufficient hard to polish. Limitation – Absorbs saliva – becomes unhygiene, leads to bacterial growth & unpleasant odour Poor esthetics Dimensional changes
Read more

Manipulation of Gypsum Product

-
MANIPULATION OF GYPSUM PRODUCTS Gypsum is manipulated in three simple steps 1. Proportioning 2. Mixing 3. Caring of the cast Rules of mixing gypsum Rule no. 1: Work Preparation     Cleanliness of the tools is the first rule for a good laboratory. Blow as well as stirring spatula must be free from plaster residue and rinsed thoroughly with clear water after cleaning with plaster solvents. Any kind of residue on the mould may cause incorrect results. The mixing ratio stipulated by the manufacturer must be observed as precisely as possible. Weighing and measuring of plaster and water ensure reproducibility. Scoop with hard plaster (negative example!!!) Rule no.2   Storage The best possible storing for unopened dental plasters is in humidity-proof containers in dry rooms at 23°C and 50%air humidity. When stored in unsuitable rooms, storage suitability decreases considerably, since temperatures that are too high or too low, or air humidity ...
Read more