Microbiology & lab The American University of

Semester spring 2025 Kurdistan

Date: 9\2\2025

Lab report

Culture media

Prepared by Supervised by
Khdher Ali
Jihan Khorsheed Assist. Prof. Dr. Rezheen
Fatah Abdulrahman, PhD
Sarmad Omar

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Objectives
1. What are culture media?
2. What do culture media need?
3. Types of culture media.
4. Culture media preparation

What are culture media?

Culture media (plural) medium (singular) are substances used to support the growth
microorganisms or cells in laboratory (in vitro). These media provide essential nutrients and
conditions that microorganisms or cells need to grow.

Materials:

 Culture media ingredients (specific to the type of media being prepared)

 Distilled water
 Carbon source
 Nitrogen source
 Mineral salt
 Buffer
 Indicators
 Selective agents
 Solidifying agent
 Growth factors such as (PH, Temperature, moisture, etc.…)

Common questions

1. What are Culture Media?

Culture media are nutrient-rich substances that provide a suitable environment for the
growth of microorganisms or cells. They can be solid, liquid, or semi-solid.

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 2. What do Culture Media Need?

Culture media need essential nutrients such as carbon sources (e.g., glucose), nitrogen
sources (e.g., peptone), vitamins, minerals, and growth factors. The media should also
have the appropriate pH, osmotic pressure, and oxygen levels.

3. Types of Culture Media:

Culture media can be classified according to

1) Physical state
2) Chemical state
3) Functional type

Physical state

Culture media can be solid or semi-solid or liquid based on the percentage of solidifying agent in
the media for example agar agar.

Agar agar: is a solidifying agent in solid culture media at different percentages. It melts at 98C o
and sets at 42Co

By different percentages we mean

Without agar agar the media will be broth or liquid

0.5 or less g/100 ml semi-solid media
1.2 g/100 ml solid media

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Type of culture Solid media Semi-solid media Liquid media (broth)
Agar agar 1.5-2% Jelly like 0.4-0.5% No agar agar
Uses 1. Isolation and To study bacterial 1. Transport
identification of motility clinical
bacteria specimens from
2. Sensitivity and Separating Motile from one place to
biochemical reactions non motiles strains another
3. To get pure culture of 2. Study
bacteria Biochemical
reactions
e.g. Macconky
broth, pepton
water, nutrient
broth

Chemical compositions and functions media

1. Defined Media: Contain known quantities of all ingredients.

2. Complex Media: Contain some ingredients of unknown composition or quantity.
3. Selective Media: Allow the growth of specific microorganisms while inhibiting
others. E.g. Macconkey ager for isolation of gram-negative and Terry bacteria.
4.

5. Differential Media: Differentiate between different types of microorganisms

based on their metabolic activity.

I. Indicator media When bacteria grow on differential media as they

produce visible characteristics or different growth patterns it helps
to distinguish between them e.g. Mcconkey Ager (ph indcator,
inhibitors, carbohydrate source)

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 The result in the upper figure lactose fermenters in pink colonies none
doctors for mentor in pale or colourless colonies

II. Mannitol salt agar to isolate STAPHYLOCOCCI because it

contains high levels of solid about 7.5% till 10% of salt NACL

It is selected for positive bacteria. This level of salt is inhibitory to

most other bacteria.

It is differential because it contains MANNITOL to sugar which

differentiate sTAPH. AUREUS from other STAPHYLOCOCCUS
species

(pH indicator phenol red at PH8.2 and yellow at pH 6.4 )

Inhibitors 7.5 till 10%

Carbohydrate source MANNITOL

Results

MANNITOL fermentation bright yellow

None MANNITOL fermentation red colour

6. Enriched Media: Contain additional nutrients to support the growth of fastidious

organisms.

I. Blood agar is made by adding 5-7%blood to the sample and it’s

base at 56C

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 blood sugar is also used as a differential medium and there are
three types of hemolysis

 Beta hemolysis producing clear area around the colony

 Alpha hemolysis appears as a greenish discoloration around
the colony
 Gama hemolysis no hemolysis

II. Chocolate agar is heated blood agar to 80 C

7. Simple media: t supports the growth of most non-fastidious bacteria.

8. Enrichment media; there are liquid media used to isolate pathogens for mixed
culture. It is incorporated with inhibitory substances to suppress the unwanted
organisms example Selenite F Broth, Tertathionate broth, rappaport vasilliadis
(RV)these are used to isolate Salmonella

9. Transport media are used to transport media or samples from the health centre to
the laboratory immediately designed to preserve the collection of microorganisms
in specimen without multiplication

 to prevent growth of contaminating microorganisms

 Prevent trying

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  Prevent unwanted bacteria
 E.g. Sturat’s media it is semi solid media

10. Anaerobic media these are designed to use anaerobic organisms reducing
substances

Examples cooked meat RCM medium that is commonly used

Table of differences;

Aspect Non-Fastidious Bacteria Fastidious Bacteria

Nutritional Requirements Can grow in simple, basic media Require complex nutrients and
with minimal nutrients. Can specific growth factors (e.g.,

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 grow in simple, basic media vitamins, amino acids).
with minimal nutrients.
Growth Conditions Adaptable to a wide range of Require precise conditions (e.g.,
environments. specific pH, temperature, or
CO2 levels).
Examples Escherichiacoli, Staphylococcus Neisseria gonorrhoeae,
aureus,Bacillus subtilis.
Haemophilus influenzae,
Streptococcus pneumoniae.
Simple Media Can grow on simple media (e.g., Cannot grow on simple media;
nutrient agar). insufficient nutrients.
Complex Media Can grow on complex media May grow on complex media if
(e.g., nutrient broth). supplemented with required
nutrients..
Defined Media Can grow on defined media Rarely grow on defined media
(exact chemical composition is unless all specific growth factors
known). are provided.
Enriched Media Do not require enriched media Require enriched media (e.g.,
for growth. blood agar, chocolate agar) for
growth.
Selective Media Can grow on selective media if May grow on selective media if
not inhibited by selective agents the media includes required
(e.g., MacConkey agar for nutrients and does not inhibit
Gram-negative bacteria). growth.
Differential Media Can be differentiated based on Can also be differentiated if the
metabolic properties (e.g., media supports their growth and
lactose fermentation on includes differential agents.
MacConkey agar).

4. Culture Media Preparation:

1. Measure and weigh the required amounts of media ingredients.
2. Dissolve the ingredients in distilled water and adjust the pH using a pH meter.

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 3. Sterilize the media using an autoclave to eliminate any contaminants.
4. Pour the sterilized media into sterile petri dishes or culture flasks and allow them
to solidify (if solid media).

In conclusion
There are many types of culture media and they are basically used to grow bacteria and examine
them in the laboratories to take advantage of it and use it in medical sectors for example using
those culture media has to go bacteria and improve medicine also to examine diseases and to
boost some vaccines to prevent contagious diseases that caused by those kind of micro
organisms.

References
1. Assist proof doctor Rezheen Fatah Ibrahim
2. https://asm.org/articles/2020/september/why-differential-selective-media-are-invaluable-
to
3. https://www.youtube.com/watch?v=cneascR3OEc
4. https://biologynotesonline.com/cultivation-of-bacteria/
5. https://www.youtube.com/watch?v=rydQVvo8rM0

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