I.P COLLEGE,CAMPUS II

A Presentation on topic

Isolation and characterization of Microbes

Submitted by-Meenu Sharma

M.Sc. biotechnology

(III SEM)

ISOLATION AND

CHARACTERIZATION OF

MICROBES

WHAT ARE MICROBES?

A microorganism or microbe is a

microscopic living organism, which

may be single-celled or multicellular.

The study of microorganisms is called

microbiology , a subject that began

with the discovery of microorganisms

in 1674 by Antonie van Leeuwenhoek ,

using a microscope of his own design

WHAT IS A CULTURE?

Population of microorganisms grown under well defined conditions.

WHAT IS MIXED CULTURE?

When a particular species of microbe is present in a very small

number in comparison to the total number of microorganisms , such

culture is called as mixed culture.

WHAT IS PURE CULTURE?

A culture containing only one species of microbe is called pure

culture.

SPECIES- a collection of bacterial cells which share an overall similar

pattern of traits in contrast to other bacteria whose pattern differs

significantly.

STRAIN- A strain is a subset of a bacterial species differing from

other bacteria of the same species by some minor but identifiable

difference.

SOME BASIC TERMS-

ISOLATION OF MICROBIAL PURE

CULTURE -Microorganisms are generallyfound in nature (air, soil andwater) as mixed populations.Even the diseased parts of plantsand animals contain a greatnumber of microorganisms,which differ markedly from themicroorganisms of otherenvironments. To study thespecific role played by a specificmicroorganism in itsenvironment, one must isolate thesame in pure culture..

COMMON METHODS OF

ISOLATION OF PURE CULTURE

I. ISOLATION BY STREAK PLATE

TECHNIQUE

II. MICRO MANIPULATOR

METHOD

III.ENRICHMENT CULTURE METHOD

IV .SERIAL DILUTION METHOD

ISOLATION METHODS

The process of screening a pure culture by separating one type

of microbes from a mixture is called Isolation. Some common

isolation methods are-

I. ISOLATION BY STREAKING OR

STREAK PLATE TECHNIQUE-

This method is used most commonly to isolate pure cultures

of bacteria.

In This method the tip of a fine structure wire loop called

Inoculation needle consist of a wooden or glass handle with a

nichrome wire the end of which is bend to form a loop is used

to transfer microbes from culture. .

The straight wires are similar to wire loop except they do not

have loop.These are used to transfer culture in colony formed

on solid culture medium.

In such cases,the colony from solid medium is streaked on the

surface of nutrient agar medium in a sterile petridish.

This technique consist of the following steps-

A. Hold the broth culture containing tube in left hand and shake it.

B. Sterilize the wire loop of the inoculation needle on burner flame .

C. Remove the cotton plug of the broth culture tube by little

finger of right hand.

D. Flame the mouth of the test tube immediately.

E. Insert the wire loop to form a thin film and replace the cotton

plug.

F. The thin film in the loop is streaked in either a zig-zag manner

by removing the loop backwards and forwards firmly.Care should

be taken that loop should not be firmly pressed against the agar

surface.

G. Incubate the petri dish in incubator at a required temperature.

H. Growth of the bacteria will be visible (after an overnight

incubation)on the streaked marks.

II-MICROMANIPULATOR METHOD-

Micromanipulators have been built, which permit one to pick out

a single cell from a mixed culture. This instrument is used in

conjunction with a microscope to pick a single cell (particularly

bacterial cell) from a hanging drop preparation.

ADVANTAGES OF MICROMANIPULATOR METHOD-

The advantages of this method are that one can be reasonably sure

that the cultures come from a single cell and one can obtain strains

with in the species.

DISADVANTAGES-

The disadvantages are that the equipment is expensive,its

manipulation is very tedious, and it requires a skilled operator.

III-ISOLATION BY USING SELECTIVE

OF ENRICHMENT

MEDIA/ENRICHMENT METHOD-

A. Generally, it is used to isolate those microorganisms, which

are present in relatively small numbers or that have slow growth

rates compared to the other species present in the mixed culture.

B. The enrichment culture strategy provides a specially designed

cultural environment by incorporating a specific nutrient in the

medium and by modifying the physical conditions of the

incubation.

C. The medium of known composition and specific condition of

incubation favors the growth of desired microorganisms but, is

unsuitable for the growth of other types of microorganisms.

D. Chemical dyes, such as malachite green and crystal violet,are used to inhibit the growth of bacteria and yeast.Sodiumazide is a metal-binding agent that inhibits the growth ofanaerobic bacteria,but does not affect the anaerobic lactic acidbacteria.

IV- SERIAL DILUTION METHOD- This method is commonly used to obtain pure cultures ofthose microorganisms that have not yet been successfullycultivated on solid media and grow only in liquid media. Amicroorganism that predominates in a mixed culture can beisolated in pure form by a series of dilutions.

The inoculum is subjected to serial dilution in a sterile liquidmedium, and a large number of tubes of sterile liquid mediumare inoculated with aliquots of each successive dilution.

The aim of this dilution is to inoculate a series of tubes with a

microbial suspension so dilute that there are some tubes showing

growth of only one individual microbe. For convenience, suppose we

have a culture containing 10 ml of liquid medium, containing 1,000

microorganisms i.e., 100 microorganisms/ml of the liquid medium.

Continued….. If we take out 1 ml of this medium and mix it with 9 ml of

fresh sterile liquid medium, we would then have 100

microorganisms in 10 ml or 10 microorganisms/ ml.

If we add 1 ml of this suspension to another 9 ml. of fresh

sterile liquid medium, each ml would now contain a single

microorganism.

If this tube shows any microbial growth, there is a very high

probability that this growth has resulted from the introduction of

a single microorganism in the medium and represents the pure

culture of that microorganism

Maintenance and Preservation of

Pure CulturesOnce a microorganism has been isolated and grown in pure culture,

it becomes necessary to maintain the viability and purity of the

microorganism by keeping the pure cultures free from

contamination. Normally in laboratories, the pure cultures are

transferred periodically onto or into a fresh medium (subculturing)

to allow continuous growth and viability of microorganisms. The

transfer is always subject to aseptic conditions to avoid

contamination. These methods include refrigeration, paraffin

method, cryopreservation, and lyophilization (freeze drying).

A.REFRIGERATION- Pure cultures can be successfully stored

at 0-4°C either in refrigerators or in cold-rooms. This method is

applied for short duration (2-3 weeks for bacteria and 3-4 months for

fungi) because the metabolic activities of the m/os are greatly

slowed down but not stopped.

Thus their growth continues slowly, nutrients are utilized andwaste products released in medium. This results in, finally, thedeath of the microbes after sometime.

B. Cryopreservation-

Cryopreservation (i.e., freezing in liquid nitrogen at -196°C)helps survival of pure cultures for long storage times. In thismethod, the microorganisms of culture are rapidly frozen inliquid nitrogen at -196°C in the presence of stabilizing agentssuch as glycerol that prevent the formation of ice crystals andpromote cell survival.

C. Lyophilization (Freeze-Drying)-

In this method, the culture is rapidly frozen at a very lowtemperature (-70°C) and then dehydrated by vacuum. Under theseconditions, the microbial cells are dehydrated and their metabolicactivities are stopped; as a result, the microbes go into dormantstate and retain viability for years.

Lyophilized or freeze-dried pure cultures and then sealed and

stored in the dark at 4°C in refrigerators. Freeze-drying method is

the most frequently used technique by culture collection centers.

Culture characterization-Bacteria grow tremendously fast when supplied with an

abundance of nutrients. Different types of bacteria will produce

different-looking colonies, some colonies may be colored, some

colonies are circular in shape, and others are irregular. The

characteristics of a colony (shape, size, pigmentation, etc.) are

termed the colony morphology.

1.Colony apperance-

Many fungi produce colonies with a fluppy appearance similar to

cotton wool .the molds produce colonies which on aging develop

a dry chalky appearance.

.A. Yeasts-

Yeast, a type of fungi (plural for fungus), is found in many

places from nature, to research labs and even everyday kitchens

for baking. Yeast colonies generally look similar to bacterial

colonies. Some species, such as candida, can grow as white

patches with a glossy surface.

For example:

ROUND YEAST COLONIES PINK YEAST COLONIES

B. BACTERIA-

Each distinct circular colony should represent an individual

bacterial cell or group that has divided repeatedly. Being kept

in one place, the resulting cells have accumulated to form a

visible patch. Most bacterial colonies appear white, cream, or

yellow in color, and fairly circular in shape.

2.Proteus vulgaris1.Bacillus subtilis 3.Staphyloccus aures

2.COLONY FORMS-

The colony shape may be circular, filamentous, rhizidoidal,

punctiform(dot like),irregular, or spindle shape.

3.COLONY ELEVATION-This form is used to describe the

depth of the colony developed by microbes.A colony may be

flat(thin film over the agar surface), raised, convex or umbonate

or with papillae surface.

4.COLONY MARGINS-The margins may be entire,

undulate(wavy), crenate, dentate , lobate, rhizoidal or

filamentous.

5.OPTICAL DENSITY-The colony may be transparent or

transluscent (foggy in appearance) or opaque(not permitting light

to pass through it ) or irrediscent (rainbow colour).

6.COLOUR-Many microbes develop colonies which are

pigmented.Such coloured substances are either water soluble or

insoluble.The soluble pigments diffuse out in the medium.

7.COLONY ODOUR--Some microbe produce a characteristic

smell which sometimes helps in identifying the microbe.