DPT - Physical state of Media

Microbiology

1. Physical state of Media Miss Areesha Ahmad Microbiology Lecturer Ph.D Scholar (Microbiology)

2. Culture Medium The food material or substances required for growing microorganisms in vitro (outside the body) is called cul t ure medium.

3. Use of culture medium It is important to grow microorganisms outside the body for the following purposes: To identify the cause of infection from the clinical sample, so that treatment can be given. To study the characteristics or properties of microorganisms. To prepare biological products like vaccines, toxoids, antigens etc..

4. Compositions of culture media Water Carbon source Nitrogen source Mineral salts Special growth factors

5. Common ingredients

6. Peptone Peptones  are  protein  hydrolysates formed by enzymatic or acidic digestion of various raw materials and many complex media contain  peptones  as the source of nitrogen.

7. Beef extract The  beef extract  is the primary source of carbon which is essential for the formation of carbohydrates in the bacteria. It also contains other components like some vitamins, different trace minerals, organic compounds, and salts, which further enhance the growth of different organisms.

8. Yeast extract Yeast extract  is a complex and widely used hydrolysate of  yeasts . It provides nitrogenous compounds, carbon, sulfur, trace nutrients, vitamin B complex and other important growth factors, which are essential for the growth of diverse microorganisms.

9. Agar It is one of the principle ingredients in the preparation of solid or semisolid media. It is used as a solidifying agent in culture medium. It is extracted from certain seaweeds belonging to genera of red algae like  Gelidium   and   Gracilaria .

10. Nutrient agar Nutrient agar  is a general purpose medium  supporting growth of a wide range of non-fastidious  organisms .

11. N utrient broth N utrient broth  is the  nutrient  agar that lack of the solidifying agent, agar powder. They remain in liquid form at room temperature and are usually used to maintain the stocks of microorganisms. In general, they are used to grow fastidious organisms .

12. enriched media Allow same type specie to grow Substances like blood, serum, egg are added to the simple medium. Used to grow bacteria that are exacting in their nutritional needs. Eg : Blood agar, Chocolate agar etc.

13. Selective Media The inhibitory substance is added to a solid media to inhibit commensal or contaminating bacteria such as: Antibiotics Dyes Chemicals Alteration of pH Examples: Thayer martin medium, Eosin methylene blue etc.

14. Differential Media Blood Agar Differentiate media are designed that differentiate bacteria on the basis of their colony color Dyes and metabolic substrates are incorporated so that those bacteria that utilize them appear as differently colored colonies. Examples: MacConkey agar, CLED, TCBS, XLD agar e tc.

15. Classification of Cultural Media Classification based on physical state: Solid medium Semi solid medium Liquid medium

16. Solid culture media Mainly used in  petri dishes as plate cultures. Can also be used in  bottles or tubes as stab (deep)  or slope cultures. Usually contain a concentration of  1-2% aga r to yield a suitable gel. Used to observe the  colonial appearance, shape, size of colony,  and the changes in the surrounding medium. Helps to  identify bacteria and differentiate  commensals from pathogens. Examples : nutrient agar, blood agar, chocolate agar, etc.

17. Semisolid culture media Prepared by adding  small amount of agar  (0.2-0.5% W/V)  to a fluid medium. Mainly used as  transport media  and for  motility testing. Examples: Amies transport medium, Cary- Blair transport medium, etc

18. Liquid culture media Do not contain  agar or solidifying agent. Growth is shown by  presence of turbidity  in the medium. Mainly used as enrichment media, biochemical testing media, and blood culture media. Examples: tryptone broth, selenite F broth, nutrient broth, etc

19. Media Preparation

20. physical condition required for growth on media There are five main physical conditions required for bacterial growth: Food pH level Temperature Time Oxygen Moisture

21. Temperature

22. pH Acidic: pH range 1-6 Neutral: pH 7 Alkaline: pH above 8

23. Gaseous requirement

24. Thank you..