Media used in microbiology.

1. Since humans take foods for energy so why don’t we take foods???

2. Various Types of Media & Plating techniques used
in Microbiology

3. Topics to be covered:
Cultivation or culture of bacteria
Purpose of culturing
Culture medium
Types of culture medium
Culturing method for microbes

4. Cultivation/Culture of Bacteria
• A microbial culture, is a method of multiplying microorganisms by
letting them reproduce in pre-determined culture media under
controlled laboratory conditions.
• Microbial cultures are used to determine the type of organisms, its
abundance in the sample being tested, or broth.

5. Types of culture media:
Defined media Complex media
A defined media refers to a medium having a
known concentration of ingredients, like sugar
(glucose or glycerol) and nitrogen source
(such as ammonium salt or nitrate as
inorganic nitrogen).
In complex media, which contain extracts and digests
of yeasts, meat, or plants, the precise chemical
composition of the medium is not known. Amounts of
individual components are undetermined and
variable. Nutrient broth, tryptic soy broth, and
chocolate agar, are all examples of complex media.

6. Functional types of Media:
• Supportive media contain nutrients that will enable a wide variety of most non-
fastidious microbes to grow. Media supplemented by blood or other special nutrients
(eg blood agar) to allow growth of organisms that cannot grow on general purpose
media. E.g. tryptic soy agar, and brain heart infusion agar.
• Enriched media is the use of certain growth media to favor the growth of a particular
microorganism over others, enriching a sample for the microorganism of interest.
Enrichment cultures are used to increase a small number of desired organisms to
detectable levels. E.g. Blood agar, Chocolate agar, Loeffler's serum, MacConkey agar,
Lowenstein-Jensen media.
• Selective media generally selects for the growth of a desired organism, stopping the
growth of or altogether killing non-desired organisms.
• Differential media takes advantage of biochemical properties of target organisms, often
leading to a visible change when growth of target organisms are present.
MacConkey agar is both selective & differential media since it have lactose and neutral
red dye bacteria's catabolize and release an acidic pigment of red colour on pink media.

7. Important components present in all types media:
Protein sources: Peptones.
Carbon / Nitrogen / Vitamin sources: Yeast extract.
Indicators: Eosin, Methylene blue, Crystal Violet… etc.,

8. Purpose of culturing:
• Isolation
• To create antigens for laboratory use
• Estimate viable counts
• Maintain stock cultures
• Long term storage of cultures

9. What is a culture medium????
The food material or substances required for
growing microorganisms in-vitro (outside the
body) is called culture medium.

10. Types of culture media:
Classification based on physical state
a) Solid medium
b) Semi-solid medium
c) Liquid medium
Classification based on ingredients
a) Simple medium
b) Complex medium
c) Synthetic or defined medium
d) Special medium

11. Classification based on physical state
• Solid medium : Agar is the most
commonly used solidifying agent.
• Semi-solid medium : Such media are
soft and are useful in demonstrating
bacterial motility and separating motile
from non-motile strains.
• Liquid medium : are sometimes
referred as broth.

12. Classification based on ingredients
I. Simple media : Nutrient agar, nutrient broth
II. Complex media : It has ingredients that exact
chemical composition is unknown.
III. Synthetic or defined media : Prepared from
pure chemical substances for research purpose
and every chemical composition is known.
IV. Special media : a) Enriched media b) Selective
media c) Differential media d) Transport media
e) Anaerobic media

13. What is agar and why its being used in media??
• Agar, also called agar-agar, gelatin-like product made primarily from the red algae Gelidium and
Gracilaria (division Rhodophyta).
• Extracted from seaweed, it is a plant-based gelatin.
• The addition of agar-agar (a complex carbohydrate extracted from seaweed) results in a solid medium. Agar is an
ideal solidifying agent for microbiological media because of its melting properties and because it has
no nutritive value for the vast majority of bacteria.
• Agar media is essential for the study of microorganisms and molecular biology and is widely used in the
culture and detection of pathogens from contaminated food and water.
• It’s a good hardening agent since microbes cannot degrade it.
• In addition, due to its porous 3D framework, agar is frequently used in biomolecular separation and
purification – Agarose Gel Electrophoresis.

14. CULTURING METHODS OF MICROBES

15. STROKE CULTURE
• Stroke culture is made in tubes
containing agar slope or slant.
• Uses: Provide a pure growth of
bacterium for slide agglutination
and other diagnostic tests.

16. Stab culture
• Prepared by puncturing with a long
straight, charged wire in a suitable
medium such as nutrient gelatin or
glucose agar.
• Uses : a) Demonstration of gelatin
liquefaction.
b) Oxygen requirements of
the bacterium under study.
c) Maintenance of stock
cultures.

18. Another method for Anaerobes cultivation via GasPak tool kit

19. The pour plate and spread plate culture
Pour plate method
• In this method the diluted microbial
sample is taken in petri dish and culture
media was added in which the agar is in
melted state.
• It is pored over the bacterial sample, which
is then mixed into the medium by gentle
agitation of the plate.
• It gives an estimate of the viable
bacterial count in a suspension.
Spread plate method
• Small volume of diluted mixture
containing approximately 30-300 cells is
transferred
• Spread evenly over surface with a sterile
bent rod
• The pour plate approach allows for more
sensitivity, so is ideal for samples with
lower bacterial numbers.

20. Diagrammatic representation of pour plate and spread plate
POUR PLATE SPREAD PLATE

21. STREAK CULTURE
• Used for the isolation of bacteria in pure culture from clinical specimens.
• One loop full of the specimen is transferred onto the surface of a well dried plate.
• Spread over a small area at the periphery.
• The inoculum is then distributed thinly over a plate by streaking it with a loop in a
series of parallel lines in different segments of the plate.
• On incubation, separated colonies are obtained over the last series of streaks.

22. Diagrammatic representation of streak culture

23. Bacterial colony morphology and its importance??
Colony morphology is the visual culture characteristics of a bacterial colony on an agar plate. Observing colony
morphology is an important skill used in the microbiology laboratory to identify microorganisms.

24. LIQUID CULTURE
• Inoculated by touching with a charged loop or by
adding the inoculum with pipettes or syringes.
• Method employed for blood culture and for
sterility tests.
• Preferable for inoculum containing antibiotics and
other antibacterial substances.
• Preferred when large yields are desired.
• Liquid culture is more suitable than agar
when working in the absence of a laminar
flow hood.

25. Some important questions from mechanism of action of medias……

26. Growth curve of bacteria….

27. Thank you Everyone

28. Questions