1. Culture media lecture (1)
Mrs. Dalia kamal eldien
Msc in microbiology

2. introduction
The study of microorganisms requires techniques for isolating from natural sources and growing them in the laboratory on synthetic media.
Thus, development of synthetic culture media and culture techniques have played important roles in the advance of this field.
culture medium is a liquid or gel, designed to support the growth of microorganisms 
Microbiologists use bacterial culture media for many purposes and applications
isolate and identify of bacteria
long-term storage of pure cultures
Antibiotic sensitivity test

3. The important reasons for culturing bacteria in vitro
diagnosing infectious diseases.
studying its morphology and its identification
obtain antigens from developing serological assays or vaccines
genetic studies

4. Basic Composition of culture media
When culturing bacteria, it is very important to provide similar environmental and nutritional conditions
bacteria need the basic nutritional conditions to grow invitro, include:
Amino Acids
Carbohydrates
Vitamins
Fatty acids
inorganic salts
Water

5. 1.Amino acid:
Are the building blocks of proteins.
‘Essential’ amino acids must be added to culture media as cells are not able to synthesize these themselves.
Example: cystine, leucine, lysine, methionine, phenylalanine, tryptophan, and valine.
2. Carbohydrates
The main source of energy is derived from sugars.
The major sugars used are glucose and galactose, however, some media contain maltose or fructose.
3.Vitamins
Serum is an important source of vitamins in culture media.
Many vitamins needed by bacteria especially group B vitamins, are necessary for cell

6. 4. Fatty Acids and Lipids
Are important in serum free media since they are normally present in serum e.g. cholesterol and steroids essential for specialized cells.
5.Inorganic Salts
The inclusion of inorganic salts in media performs several functions.
Primarily they help to retain the osmotic balance of the cells and help regulate membrane potential by provision of sodium, potassium and calcium ions.
6. Water
All bacteria require some amount of water.
Buffering Systems
Most cells require pH conditions in the range and close control of pH is essential for optimum culture conditions.

7. Classification:
Bacterial culture media can be classified in at least three ways;
Based on consistency
Based on nutritional component
Based on its functional use.
Classification based on consistency, Culture media are
liquid
semi-solid
solid
biphasic.

8. Liquid media:
These are available for use in test-tubes, bottles or flasks, sometimes referred as “broth” (e.g nutrient broth).
In liquid medium, bacteria grow producing turbidity.
Certain aerobic bacteria and those containing fimbriae (Vibrio & Bacillus) are known to grow as a thin film called ‘surface pellicle’ on the surface of broth.
Sometimes the initial turbidity may be followed by clearing due to autolysis, which is in penumococci.
Long chains of Streptococci when grown in liquid media tend to entangle and settle to the bottom forming granular deposits
Inoculating in the liquid medium also helps to dilute any inhibitors of bacterial growth. This is the practical approach in blood cultures.

9. Sterile Liquid media(right) turbid liquid media(left)

10. Liquid media show the surface pellicle

11. Solid media:
Any liquid medium can be rendered by the addition of certain solidifying agents. Agar agar (simply called agar) is the most commonly used solidifying agent.
Agar is a polysaccharide obtained from the cell membranes of some species of red algae
It melts at 90-95oC and solidifies at 32–39 C.
doesn’t contribute any nutritive property
However, it may be a source of calcium & organic ions.
it is used at concentration of 1.5% w/v to make a solid agar medium.
Solid media are used mainly in Petri dishes as plate
cultures.
Also in bottles or tubes as stab (deeps) or slope cultures.

12. Solid media in petri-dish

13. Semi-solid agar:
Reducing the amount of agar to % renders a medium semi-solid
useful in demonstrating bacterial motility
Certain transport media such as Stuart’s and Amies media are semi-solid in consistency
Hugh & Leifson’s oxidation fermentation test medium as well as mannitol motility medium are also semi-solid.

14. Motility test in semi-solid media

15. Identify?

16. Biphasic media:
Sometimes, a culture system comprises of both liquid and solid medium in the same bottle. This is known as biphasic medium (Castaneda system for blood culture).
The inoculums is added to the liquid medium and when subcultures are to be made, the bottle is simply tilted to allow the liquid to flow over the solid medium.

17. Biphasic Medium

18. Besides agar, egg yolk and serum too can be used to solidify culture media. While serum and egg yolk are normally liquid, they can be rendered solid by coagulation using heat.
Serum containing medium such as Loffler's serum slope and egg containing media such as Lowenstein Jensen medium and Dorset egg medium are solidified as well as disinfected by a process of inspissations

19. Loffler's serum & LJ