The document discusses the screening of microorganisms, which involves the isolation and detection of specific microbes from mixed populations using selective procedures. It describes various types of screening, including primary and secondary screening techniques, and methods for identifying antibiotic, organic acid, and extracellular metabolite producing microorganisms. Additionally, it outlines the significance of these screening processes in isolating commercially valuable microbes and the importance of understanding their growth conditions and metabolic products.

1. Screening of microorganisms
Types of Screening
Presented By-
Mr. Pathan Arshad khan I.A.
Assistant Professor
Gramin Science College, Vishnupuri,
Nanded.

2. Screening
The procedure of isolation, detection and separation
of microorganism of our interest form a mixed
population by using highly selective procedure is
called Screening.

3. Microorganisms
Sources
Food (Milk,
Cheese etc.)
Environment
(Air, Water,
Soil, etc.)
Compost and
other sources
Screening
Secondary Screening
Primary Screening

4. Things to be considered while
screening……
 Choice of Sources-
Samples from screening is taken from milk, water,
soil, air, compost etc.
 Choice Substrate-
Nutrients and growth factors should be supplied for
growth of desired microorganism.
 Choice of Detection-
Proper isolation and detection of desired Microorganisms
is important.

5. Screening
Types of Screening:-
Primary
Screening
Secondary
Screening
Organic Acid
producing
microorganisms
Antibiotic
producing
microorganisms
Extracellular
metabolite
producing
microorganism
Enrichment
culture
techniques
By Using
Dye
By using crowded
plate technique By Auxanography
Technique
By Defined media

6. Primary Screening
 It’s a process of isolation, detection and separation of
microorganism of our interest.
 Determines which microorganisms are able to produce a
compound.
 Does not provide much idea about the production or yield
potential of microorganism.
 It separate out only a few microorganisms, only few have
commercial value while discard the valueless microorganism.

7. 1.Primary Screening of organic acid producing
microorganism
 The pH indicating dye may be used for detecting
microorganism that are capable of producing organic acid.
 These dye undergo color change according to its pH .
 Dye such as Neutral red, Bromothymol blue are added to
poorly buffered nutrient agar medium.
 Colonies are subcultured to make stock culture.
 Further testing is needed since inorganic acid bases are also
metabolic product of microbial growth.

9. 2.Primary Screening of antibiotic producing
microorganism
 Crowded plate technique is used for screening of antibiotic producing
microorganisms.
 Does not give information about the sensitivity of antibiotic towards
other microorganisms.
 Dilutions are made and then pouring & spreading soil samples that
gives 300-400 or more colonies per plate.
 Colonies showing antibiotic activity are indicated by zone of
inhibition around the colonies.
 Such colonies are subcultured and purified by streak before making
stock culture.
 The purified cultures is then tested to find the microbial inhibition
spectrum

10. Crowded Plate Technique

11. 3.Primary Screening of extracellular metabolite producing
microorganism
 Auxanography technique is used for detecting microorganisms able to
produce growth factors, vitamins, amino acids etc. extracellularly.
 Two major steps are—
 A filter paper strip is put across the bottom of petri-dish.
 The nutrient agar is prepared and poured on paper disc and allow to
solidify.
 Soil sample is diluted and proper dilutions are inoculated.
 A minimal media lacking the growth factors is prepared and seeded
with test organism .
 The seeded medium is poured on to fresh petriplates and the plate is
allowed to set
A.) Preparation of First Plate
B.) Preparation of First Plate

12.  The agar in first plate is then lifted and placed on second plate
without inverting.
 The growth factor produced on agar can diffuse in to lower layer
containing test organism.
 The zone of stimulated growth test organism around colonies are an
indication of organism produce growth factor extracellularly.

13. 4.Primary Screening by enrichment culture
 This was designed by Beijerinck to isolate desired microorganism
from heterogeneous microbial population.
 It consist of following steps-
a. Nutrient broth is inoculated with microbial source material
and incubated .
b. A small portion of all inoculums are plated on to the solid
medium and well isolated colonies are obtained.
c. Suspected colonies from the plate are subcultured on fresh
media and subjected for further testing.

14. Enrichment Culture

15. Secondary Screening
 It’s a systematic screening program intended to isolate
industrial important or useful microorganism.
 It is useful in sorting of microorganism that have real
commercial value.
 The microorganism that having poor applicability in
fermentation process are discarded.
 It provide the information whether the product formed by
microorganism is new or not.
 This may be accomplished by Paper chromatography, Thin
Layer chromatography techniques.

16.  It should shows whether the product possess physical
properties such as UV light absorption or fluorescence or
chemical properties that can be employed to detect the
compound during paper chromatography.
 It is conducted on agar plates, in flask or in small fermentor
containing liquid media.
 It gives an idea about the economic position of fermentation
process involving the use of a newly discovered culture.
 It help in providing information regarding the product yield
potential of different isolates.

17.  It determines the optimum condition of growth or
accumulation of a product associated with particular culture.
 Chemical, Physical and Biological properties of product are
also determined during secondary screening.
 It detect gross genetic instability in microbial cultures. This
type of information is very important, since microorganisms
tending to undergo mutation or alteration is some way may
lose there capability for maximum accumulation of the
fermentation products.
 It tells about chemical stability of the fermentation product.
 It can be qualitative or quantitative in its approach

18. Examples of Secondary Screening
Antibiotic producing Streptomyces species.
 Streptomyces isolate are streaked as narrow band on
sterilized nutrient agar plate and incubate.
 Test organisms are then streaked from the edge of plates
without touching streptomyceal isolates and then the plates
are incubated.
 At the end of incubation growth inhibitory zones for each
organisms are measured in millimeters.
 Such organisms are again subjected for further testing by
growing the culture in sterilized liquid media and incubated
at constant temperature in mechanical shaker .

19. Thank you !!