Types of media

Media helps to grow different microbes making it easier to study for research purpose.

1. TYPES OF culture MEDIA SUBMITTED TO :- SUBMITTED BY :- Dr. Suman Upadhyaya Anikesh Kr. Singh M.Sc. FMT (1 st Sem ) DEM - BBAU

2. CULTURE MEDIUM The food material on which microorganisms are grown in the laboratory is known as medium (pl. media ) and the growth itself is called a culture .

3. Types of culture media Culture media can be classified on the basis of following characterstics : Consistency Composition Purpose

4. ON THE BASIS OF consistency Solid medium Semi-solid medium and L iquid medium

5. SOLID MEDIum ' Agar ' is most commonly used to prepare solid medium.  Solid medium contains agar at a concentration of 1.5-2.0% . Agar is golden-yellow granular powder obtained from seaweed.

6. CONT…  It is basically a polysaccharide extract . Agar is an ideal solidifying agent as it is : Bacteriologically inert, i.e. no influence on bacterial growth. It remains solid at 37°C. It is transparent.

7. Cont… Solid medium has physical structure and allows bacteria to grow in physically informative or useful ways (e.g. as colonies or in streaks). Advantages of solid media: Bacteria may be identified by studying the colony character . Mixed bacteria can be separated. Solid media is used for the isolation of bacteria as pure culture.

8. 2. Semi-solid medium They are prepared with agar at concentrations of 0.5% or less. They have soft custard like consistency. They are useful in demonstrating bacterial motility and separating motile from non-motile strains.

9. 3. Liquid medium They are sometimes referred as “ broth ”. These media contains specific amounts of nutrients but don’t have any trace of gelling agents such as gelatin or agar. Broth medium serves various purposes such as propagation of large number of organisms, fermentation studies, and various other tests. e.g. sugar fermentation tests.

10. Cont… It is difficult to identify all type of microorganisms in liquid medium. Suitable for the isolation of bacteria from blood culturing and water analysis.

11. ON THE BASIS OF COMPOSITION Synthetic or chemically defined medium :- A chemically defined medium is one prepared from purified ingredients and whose exact composition is known . It provides trace elements and vitamins required by the microbe and especially a defined carbon and nitrogen source. 

12. CONT… Glucose or glycerol are often used as carbon sources, and ammonium salts or nitrates as inorganic nitrogen sources. eg : peptone water – 1 % peptone + 0.5% NaCl in water.

13. Non synthetic or chemically undefined medium :- Non-synthetic medium contains at least one component that is neither purified nor completely characterized. Undefined  medium has some complex ingredients, such as yeast extract, which consists of a mixture of many, many chemical species in unknown proportions. For example- Nutrient broth , is derived from cultures of yeasts

14. ON THE BASIS OF PURPOSE General purpose media/ Basal Media. Enriched medium. Selective medium. Differential/ indicator medium. Transport media. Anaerobic media. Assay media.

15. Basal media Basal media are basically simple media that supports most non-fastidious bacteria. Peptone water, nutrient broth and nutrient agar are considered as basal medium. These media are generally used for the primary isolation of microorganisms.

16. Nutrient Agar

17. Enriched mediu m Addition of extra nutrients in the form of blood, serum, egg yolk etc, to basal medium makes them enriched media. Enriched media are used to grow nutritionally exacting ( fastidious ) bacteria.

18. Cont… Blood agar, chocolate agar, Loeffler’s serum slope etc., are few of the enriched media. Blood agar is prepared by adding 5-10% (by volume) blood to a blood agar base. Choclate agar   is also known as heated blood agar or lysed  blood agar .

19. Blood Agar ChoclateA gar

20. Selective medium Selective and enrichment media are designed to inhibit unwanted commensal or contaminating bacteria and help to recover pathogen from a mixture of bacteria. While selective media are agar based, enrichment media and are liquid in consistency .

21. Cont… Any agar media can be made selective by addition of certain inhibitory agents that don’t affect the pathogen of interest. Various approaches to make a medium selective include  addition of antibiotics, dyes, chemicals, alteration of pH or a combination of these.

22. Cont… Examples of selective media include: Thayer Martin Agar used to recover   N.gonorrhoeae . It usually contains the following combination of antibiotics: Vancomycin : which is able to kill most Gram-positive organisms. Colistin ,: which is added to kill most Gram-negative organisms except Neisseria . Nystatin ,: which can kill most fungi. Trimethoprim : which inhibits Gram-negative organisms.

23. Cont… Eosin methylene blue : selective for gram negative bacteria The dye methylene blue in the medium inhibit the growth of gram positive bacteria

24. Cont… Lowenstein –Jenson medium is a solid medium used for Mycobacterium tuberculosis. It contain penicillin, nalidixic acid and malachite green to inhibit growth of gram positive and gram negative bacteria, in order to limit growth to Mycobacteria species only.

25. Cont… Mannitol Salt Agar  and Salt Milk Agar used to recover  S.aureus  contains 10% NaCl . Selective media such as  TCBS Agar  used for isolating  V. cholerae  from fecal specimens have elevated pH (8.5-8.6), which inhibits most other bacteria.

26. Cont… MacConkey’s Agar used for   Enterobacteriaceae members contains bile salt that inhibits most gram positive bacteria . Wilson and  Blair’s Agar for recovering  S. typhi  is rendered selective by the addition of dye brilliant green.

27. Differential/ indicator medium Certain media are designed in such a way that different bacteria can be recognized on the basis of their colony colour. Various approaches include incorporation of dyes, metabolic substrates etc, so that those bacteria that utilize them appear as differently coloured colonies. Differential media allow the growth of more than one microorganism of interest but with morphologically distinguishable colonies.

28. Cont… Examples of selective media include: MacConkey medium : Distinguish between lactose fermenters & non lactose fermenters . • Lactose fermenters – Pink colonies • Non lactose fermenters – colorless colonies

29. Cont… Xylose Lysine Deoxycholate Agar(XLD): Used for the recovery of Salmonella and Shigella species .

30. Cont… Cysteine Lactose Electrolyte Deficient Agar(CLED): For cultivation of pathogen from urine specimen, inhibit swarming of proteus sp. CLED, serratia

31. Transport media Transport media is used for transporting the samples. Clinical specimens must be transported to the laboratory immediately after collection to prevent overgrowth of contaminating organisms or commensals . This can be achieved by using transport media.

32. Cont… Such media prevent drying (desiccation) of specimen, maintain the pathogen to commensal ratio and inhibit overgrowth of unwanted bacteria. Eg : – Stuart’s medium – Buffered glycerol saline

33. Cont… Cary Blair transport medium and VenkatramanRamakrishnan (VR) medium are used to transport feces from suspected cholera patients. Sach’s buffered glycerol saline is used to transport feces from patients suspected to be suffering from bacillary dysentery. Pike’s medium is used to transport streptococci from throat specimens.

34. Anaerobic media These media are used to grow anaerobic organisms. Anaerobic bacteria need special media for growth because they need low oxygen content, reduced oxidation –reduction potential and extra nutrients . Media for anaerobes may have to be supplemented with nutrients like hemin and vitamin K.

35. Cont… Such media may also have to be reduced by physical or chemical means. Addition of 1% glucose, 0.1% thioglycollate , 0.1% ascorbic acid, 0.05% cysteine or red hot iron filings can reduce dissolve oxygen. Before use the medium must be boiled in water bath to expel any dissolved oxygen and then sealed with sterile liquid paraffin.

36. Cont… Example of anaerobic media are: Robertson Cooked Meat (RCM) medium is commonly used to grow  Clostridium   spps . Thioglycollate broth contains sodium thioglycollate , glucose, cystine , yeast extract and casein hydrolysate .

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