1) Culture media are used to grow microorganisms and can take liquid or solid forms. They must provide the necessary physical, chemical, and organic requirements for microbial growth. 2) There are several types of culture media including general purpose, selective, enrichment, differential, and chemically defined media. Each type is designed for specific purposes like isolating organisms or distinguishing between types. 3) The production of culture media involves weighing and dissolving ingredients, adjusting the pH, dispensing the media, and sterilizing it through autoclaving or boiling to kill any microbes.

1. Different media used in
Food microbiology
Arun Kr. Gupta
MSc. Food Science & Technology
Ist yr.
15396012

2. Introduction
The study of microorganisms requires techniques for isolating cells
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 advancement
of this field. Microbiologists use bacterial culture media for many
purposes and applications.

3. Media :
The nutrient preparation on or which a culture is grown in the
laboratory is called culture medium. Media are used to isolate and
identify bacteria, reveal their metabolic properties, and allow long-
term storage of pure cultures.
Key terms
 Culture medium: Nutrients prepared for microbial growth
 Sterile: No living microbes
 Inoculum: Introduction of microbes into medium
 Culture: Microbes growing in/on culture medium

4. Requirements for Growth
Physical requirements
 Temperature
 pH
 Osmotic pressure
Chemical requirements
 Carbon
 Nitrogen, sulfur, and phosphorous
 Trace elements
 Oxygen
Organic growth factor

5. Bacteria nutritional requirements
 Generalists (which are able to use a wide range of nutrients) and/or nutrients
that are commonly available.
 Auxotroph's because, even given a carbohydrate carbon source, they cannot
synthesis one or more organic molecules required for their growth – these
molecules must be also provided in growth media.
 Fastidious, meaning that they have very specific and/or complex nutritional
requirements. These species do not grow because they cannot use one or more
nutrients in the form provided in the medium (e.g., they might require H2S
rather than SO4 as a sulphur source), have requirements for very specific types
of nutrients

6. Purpose of culture media:
Culture media serve a number of purposes in practical microbiology. They can be
used to:
 Grow a wide range of organisms in a particular group, e.g. bacteria
 Maintain organisms in culture collections;
 Distinguish b/w different types of microorganisms;
 Select specific groups or types of microorganisms from an environment, e.g. a
food material;
 Help identify microorganisms;
 Assay nutrient or antimicrobial compounds.

7. Classification of media
• Liquid ( broth)
• Solid (Agar)
Ingredients.
•Simple (2-5 ingredients)
•Complex (>5 ingredients)
Origin
•Natural
•Synthetic
Functionality
•Selective
•Differential
State

8. The types of culture media recognized are:
1. General purpose (non-selective)
2. Selective
3. Enrichment
4. Differential
5. Selective and differential
6. Chemically defined
7. Elective
8. Living
Note: There is not always a clear distinction between one type and another, e.g. a
medium can be both selective and chemically defined.

9. Cont.
 General purpose: general purpose media have a nutritional content that will allow
the growth of a wide range of either bacteria or yeasts and mold. Media of this type
is often complex, prepared from natural products such as meat, yeast and vegetable
extracts and hydrolysis products of meat.
Ex: For the bacterial growth are nutrient agar/broth, plate count agar & for molds/
yeasts malt extract agar/ broth, potato dextrose agar.
 Selective media: selective media are those which permit the growth of some
specific group or type of organism while preventing or retard or inhibiting the
growth of others, thus facilitating bacterial isolation.
Selection can be operate in a number of ways:
1. Selection on the basis of pH e.g. citric acid in citric acid agar for the isolation of
fungi.
2. Selection on the basis of water activity- high salt or sugar concentration for
halophilic or osmophilic organisms.
Ex: EMB (Eosin methylene Blue): E.coli and related species produce colonies with a
brilliant green metallic sheen. On the same medium Aerobacter aerogenes and related
species produces pink colonies with a dark centres.

10.  Enrichment media:
Enrichment media are broths contain selective ingredients and are designed to shift the growth of a
mixed population of bacteria in the direction of a specific organism or group of organisms so that
these organisms become dominant, increase in number and are therefore easier to isolate.
Ex: Selenite broth for the isolation of Salmonella from mixed population.
 Differential media:
Differential media cause certain colonies to develop differentially from other organism present by
producing a characteristics change in the bacterial growth and or the medium surrounding the
colonies. These media are used for distinguishing among morphologically and biochemically
related groups of organism.
Ex: Blood agar is a differential media used to differentiate haemolytic properties of Streptococci
by their action on the medium.
 Selective/ differential media: selective/ differential media used extensively for the isolation of
specific organism. It is designed to isolate a group of closely related organisms and
differentiate b/w them. Ideally, media used for the analysis of foods for specific organisms
should be totally specific for the organisms.
Ex: Salmonella Shigella Agar: it is used for the isolation of salmonella & some shigella species
from the pathological specimens, suspected foods etc.

12.  Chemically defined media: chemically defined media are those in which the
detailed composition of the medium is known in terms of the chemical in nature of
each individual component and the quantity present. Chemically defined media can
be general purpose or selective and/or differential.
Ex: Minerals modified glutamate medium, which is used for the enumeration of
coliforms in water is both selective and differential.
 Elective medium: Elective media are designed to promote the growth of specific
organisms that have special nutritional requirements by adding a particular
ingredient to the medium so that their growth is improved.
Ex: tomato juice agar is used for culturing lactobacilli, it contain some ingredients but
they are not selective agents and the medium will grow a wide range of other
microorganism, including bacteria, yeasts, molds.
 Living media: Some microorganism, e.g. viruses, will only grow in the living cells
of their host. In order to culture them in the laboratory a living culture of host cells
needs to be provided.
e.g. chick embryos or tissue cultures. Bacteriophages viruses are grown on bacterial
cultures.

13. Basic method for the production
of culture media
 Weigh out the ingredients
 Dissolve in water (this may require boiling if agar is present)
 Adjust pH
 Dispense in suitable containers (conical flask, tubes)
 Sterilize by autoclaving (121 C for 15-20 min. for neutral media, 115 C
for 10 min for acid media) or boil for some selective media

14. Thank you for your kind attention.