2. Content
Definition
Uses of culture media
Basic composition of culture media
Types of culture media
Based on physical state
1. solid medium
2. semi solid medium
3. liquidmedium
Based on ingredients
1. Simple or basal medium.
2. Complexmedium.
3. Synthetic or defined medium.
4. Semisynthetic medium.
5. Special medium
Media preparation
3. Definition
🞄The food material or substances required for growing
microorganisms in vitro (outside the body) is called culture
medium
4. Uses of culture
media
🞄It is important to grow microorganisms outside the body for the
following purposes:
🞄1. to identify the cause of infection from the clinical sample, so
that proper treatment can be given.
🞄2. to study the characteristics or properties of microorganisms.
🞄3. to prepare biological products like vaccines, toxoids,
antigens…etc.
5. Basic
ingredient of
culture
media
WATER- source of hydrogen and oxygen.
Pepton
- Complex mixture of digested protein
- It contains proteoses, aminoacids, polypeptides, phosphates, minerals
and accessory growth factor like nicotinic acid and riboflavin
Electrolytes : sodium chloride
6. AGAR
- It is prepared for using solid media.
- Obtained from sea weeds.
- Long chain polysaccharides.
- Also contains varying amounts of inorganic salts and small
quantities of a protein – like substance.
- Hydrolysed at high temperature at high acid or alkaline ph.
- Melts at 98ºC and usually sets at 42ºC depending on agar
concentration.
- Approximately 2% agar is used to prepare solid media.
Blood or serum
-These are used for enriching culture media
7. Types of
culture media
🞄I.Classification based on physical state
a) solid medium
b) semi solid medium
c) liquid medium
🞄II.Classification based on the ingredients
a) simple medium
b) complex medium
c) synthetic or defined medium
d) Special media
9. 🞄 Semi-solid media
Such media are soft and are useful in
demonstrating bacterial motility and separating
motile from nonmotile strains
🞄 Liquid media
are sometimes referred as “ broth “.
bacteria grow uniformly producing general
turbidity e.g. Nutrient broth
10. Based on the
ingredients
🞄Simple media
eg: Nutrient broth, glucose broth,Nutrient agar
- NB consists of peptone, meat extract, NaCl
- NB + 2% agar = Nutrient agar
- Simplest and routinely employed method
🞄Complex media
such as blood agar, it has ingredients that exact components are
difficult to estimate.
11. Synthetic or defined media
•specially prepared media from pure chemical substances for
research purpose and composition of every component is well
known
• egg: peptone water – 1% peptone + 0.5% NaCl in water.
12. Special media
- Enriched media
- Enrichmentmedia
- Selective media
- Differential media
- Indicator media
- Transport media
- Anaerobic media
13. Special media
Enriched media
- Substances like blood, serum, egg are added to the simple
medium.
- Used to grow bacteria that are exacting in their nutritional needs.
Blood agar Chocolate agar
14. Blood agar
contains mammalian blood(usually sheep or horse)
typically at a concentration of 5-10%,
used to isolate fastidious organisms and
detect haemolysis
Chocolate agar
contain red blood cells that have been lysed by
slowly heating to 80 c .and it used for growing
fastidious bacteria;
such as Haemophilus influenzae
15. Enrichment
media
🞄Has stimulating effect on bacteria to be grown or inhibits its
competitors
🞄Results in absolute increase in number of wanted bacteria related
to other bacteria
🞄Useful for culture of faeces where non-pathogenic being
overgrown by pathogenic. Eg Salmonella being overgrown by E.
coli
🞄Eg.Tetrathionate broth and alkaline peptone water
16. Selective
media
Isolates particular bacteria
The inhibitory substance is added to a solid media to inhibit
commensal or contaminating bacteria such as :
- Antibiotics, Dyes,Chemicals
Examples
🞄Deoxycholate citrate agar (DCA) : for enteric bacilli ( Salmonella,
Shigella)
🞄Bile salt agar : for vibrio cholerae
17. Eosin methylene blue
- selective for gram negative bacteria
-The dye methylene blue in the medium
inhibit the growth of gram positive bacteria.
Campylobacter agar
- Is used for isolation ofCampylobacter jejuni from
faecal or rectal swab.
-Contain Bacteriological charcoal ,Cefoperazone
andAmphotericin B.
18. Lowenstein –Jenson medium
- is solid medium used for Mycobacterium tuberculosis.
- 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
19. Differential
media
- are designed in such a way that different bacteria can be
recognized on the basis of their colony colour.
- Dyes and metabolic substrates are incorporated so that those
bacteria that utilize them appear as differently coloured colonies.
🞄Examples:
- MacConkey agar
-TCBS agar
- XLD agar
20. MacConkey medium
- Distinguish between lactose fermenters
& non lactose fermenters.
- Lactose fermenters – Pink colonies
- Non lactose fermenters – colourless colonies
Xylose Lysine DeoxycholateAgar(XLD)
- Used forSalmonella and
Shigella species.
22. Indicator
media
🞄Contains an indicator which changes color when a bacterium
grows in them.
🞄Salmonella typhi grow as black colonies on Wilson and blair
medium containing sulphite
🞄 MacConkey’s agar : pink colonies in presence of neutral red
indicator
23. Transport
media
- Media used for transporting the samples.
- Delicate organisms may not survive the time taken for
transporting the specimen without a transport media.
• Eg –Stuart’s medium : reducing agent (prevents oxidation),
charcoal (neutralise bacterial inhibitor), used for gonococci
- Buffered glycerol saline : enteric bacilli
24. Sugar media
🞄 Contains 1% of sugar in peptone water along with an indicator
(Andrade’s indicator-0.005%)
🞄 a small tube(durham’s tube) is kept inverted in the larger sugar
tube to detect gas production
25. Anaerobic
media
🞄These media are used to grow anaerobic organisms.
- Eg: Robertson’s cooked meat medium.
Thioglycolate broth medium
26. Dehydrated
media
🞄Simply reconstituted in distilled water and sterilised before use
🞄With dehydrated media, the process of media making has become
simpler and its quality more uniform.
28. Streak culture
It is the most common inoculation method ; used for the inoculation of the
specimens on to the solid media . It is also used for obtaining individual isolated
colonies from a mixed culture of bacteria .
29. Lawn culture
🞄Employed in antibiotic sensitivity testing and in bacteriophage
typing
🞄Lawn culture is obtained by flooding the surface of the plate with
a liquid culture or suspension of bacterium
🞄Culture plate is kept for minute and the excess material is poured
off
🞄Alternatively, the culture plate may be inoculated by a sterile swab
soaked in liquid bacterial culture
🞄Plate is then incubated at 37C overnight to obtain bacterial
colonies