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Culture media(1)
Prof. Dalia M. mohsen
Prof. in Microbiology
Prof. Dalia M. Mohsen
Lecture (1)
Prof. Dalia M. Mohsen
Objectives
 Introduction to culture media
 Common consistent of culture media
 Different methods of Classification
 Classification based on concentration of agar
Prof. Dalia M. Mohsen
Introduction
 The study of microorganisms requires techniques for
isolating from natural sources and growing them in the
laboratory on synthetic media.
 culture medium: Liquid or gel.
 Support the growth of microorganisms .
 Microbiologists use bacterial culture media for many
purposes and applications
1. isolate and identify of bacteria.
2. long-term storage of pure cultures.
3. Antibiotic sensitivity test.
Prof. Dalia M. Mohsen
 The important reasons for culturing bacteria in vitro
1. Diagnosing infectious diseases.
2. Studying its morphology and its identification
3. Obtain antigens from developing serological assays or
vaccines
4. Genetic studies
Prof. Dalia M. Mohsen
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
in-vitro, include:
 Amino Acids
 Carbohydrates
 Vitamins
 Fatty acids
 inorganic salts
 Water
Prof. Dalia M. Mohsen
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.
Prof. Dalia M. Mohsen
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
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.
Prof. Dalia M. Mohsen
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 bacteria require pH conditions in the range 7.27.4 and close control of pH is essential for optimum
culture conditions.
Prof. Dalia M. Mohsen
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.
Prof. Dalia M. Mohsen
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.
 Inoculating in the liquid medium also helps to dilute any
inhibitors of bacterial growth (blood cultures).
 The growth of the bacteria on the fluid media give either
granular or uniform turbidity
 Sometimes the initial turbidity may be followed by clearing
due to autolysis, which is in penumococci.
Prof. Dalia M. Mohsen
Sterile Liquid media(right) turbid liquid
media(left)
Prof. Dalia M. Mohsen
Liquid media show the surface
pellicle
Prof. Dalia M. Mohsen
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 90-95C and solidifies at 32–39 C.
 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
 Also in bottles or tubes as stab (deeps) or slope
cultures.
Prof. Dalia M. Mohsen
Solid media in petri-dish
Prof. Dalia M. Mohsen
Semi-solid agar:
 Reducing the amount of agar to 0.4-0.5% renders a
medium semi-solid
 useful in demonstrating bacterial motility
 Common example include:- Transport media such
as Stuart’s and Amies media.
Prof. Dalia M. Mohsen
Motility test in semi-solid media
Prof. Dalia M. Mohsen
Identify?
Prof. Dalia M. Mohsen
Biphasic media:
 Sometimes, a culture system comprises of both liquid
and solid medium in the same bottle. This is known as
biphasic medium (e.g. Castaneda system for blood
culture).
Prof. Dalia M. Mohsen
Biphasic Medium
Prof. Dalia M. Mohsen
 Besides agar, egg yolk and serum 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
Define inspissations???
Prof. Dalia M. Mohsen
Loffler's serum & LJ
Prof. Dalia M. Mohsen
Prof. Dalia M. Mohsen