Name: microbial colony isolation methods
Uploaded: 2025-06-12T09:41:06.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Biology

BIO.4

BIO.4.b

techniques-for-isolation-of-pure-cultures

Techniques for Isolation of Pure Cultures

Les cultures pures ou axéniques sont constituées d’un seul type de micro-organisme. Ils sont essentiels pour étudier les caractéristiques des espèces individuelles. La méthode de la plaque striée isole les colonies pures sur des milieux solides. Une boucle d’échantillon est striée à la surface de la gélose dans des zones successives. Chaque traînée réduit la densité cellulaire, ce qui permet aux cellules isolées de la zone terminale de former des colonies distinctes. La méthode de la plaque d’étalement utilise un épandeur stérile pour répartir uniformément une suspension microbienne diluée sur une surface de gélose, permettant ainsi à des colonies distinctes de se former à partir de cellules individuelles. Dans la technique de la plaque versée, la suspension microbienne diluée est ajoutée à une plaque stérile, puis une gélose fondue suffisamment refroidie est versée sur le dessus et mélangée. De cette façon, les colonies se développent à l’intérieur et à la surface de la gélose, ce qui rend la technique utile pour isoler les organismes aérobies et anaérobies. Les micro-organismes de type diatomée sont cultivés dans des milieux liquides. Les cultures pures sont obtenues par enrichissement sélectif ou dilutions en série jusqu’à l’obtention d’un seul organisme. Leur pureté est vérifiée après l’incubation à l’aide de techniques telles que la microscopie.

techniques d’isolement de cultures pures

Les micro-organismes sont r&#233;guli&#232;rement cultiv&#233;s en laboratoire &#224; l&#8217;aide de diverses techniques visant &#224; les isoler, les faire cro&#238;tre et les quantifier pour une &#233;tude approfondie. Ces m&#233;thodes reposent sur l&#8217;inoculation des micro-organismes dans un milieu de culture adapt&#233;, dans des conditions aseptiques, afin d&#8217;&#233;viter toute contamination. Selon l&#8217;objectif vis&#233;, l&#8217;inoculation peut impliquer un transfert direct ou l&#8217;utilisation de suspensions bact&#233;riennes dilu&#233;es comme inoculum.
M&#233;thode de l&#8217;ensemencement en stries pour l&#8217;isolement
La m&#233;thode de l&#8217;ensemencement en stries est une technique courante utilis&#233;e pour obtenir des colonies microbiennes pures. Elle consiste &#224; &#233;taler un &#233;chantillon &#224; la surface d&#8217;un agar selon un sch&#233;ma de stries successives. Cette dilution progressive r&#233;duit la densit&#233; cellulaire &#224; chaque passage, aboutissant &#224; l&#8217;isolement d&#8217;organismes dans les zones terminales de la bo&#238;te stri&#233;e. Apr&#232;s incubation, ces cellules isol&#233;es prolif&#232;rent pour former des colonies visibles et distinctes, indispensables &#224; l&#8217;&#233;tude de cultures pures et &#224; la r&#233;alisation d&#8217;analyses ult&#233;rieures.
M&#233;thode de l&#8217;ensemencement en surface pour la quantification
La m&#233;thode de l&#8217;ensemencement en surface est largement utilis&#233;e pour quantifier les micro-organismes pr&#233;sents dans une suspension. Un volume mesur&#233; de la suspension bact&#233;rienne est r&#233;parti uniform&#233;ment &#224; la surface d&#8217;une bo&#238;te d&#8217;agar solidifi&#233; &#224; l&#8217;aide d&#8217;un &#233;taleur st&#233;rile, tel qu&#8217;une tige en verre ou en m&#233;tal. Apr&#232;s incubation, les micro-organismes se d&#233;veloppent en colonies isol&#233;es &#224; la surface de l&#8217;agar. En comptant les colonies et en tenant compte de la dilution de l&#8217;inoculum, il est possible de calculer la concentration de micro-organismes viables dans l&#8217;&#233;chantillon initial.
M&#233;thode de l&#8217;ensemencement en profondeur pour la quantification
Dans la m&#233;thode de l&#8217;ensemencement en profondeur, une suspension bact&#233;rienne mesur&#233;e est m&#233;lang&#233;e &#224; de l&#8217;agar fondu refroidi &#224; temp&#233;rature ambiante (environ 45&#8211;50 &#176;C), puis vers&#233;e dans une bo&#238;te de P&#233;tri st&#233;rile. L&#8217;agar se solidifie, emprisonnant certaines cellules dans le milieu, tandis que d&#8217;autres restent &#224; sa surface. Apr&#232;s incubation, des colonies se d&#233;veloppent &#224; la fois dans l&#8217;agar et &#224; sa surface. Cette technique est utile pour la culture et la quantification de bact&#233;ries a&#233;robies et microa&#233;rophiles. Dans certaines conditions, des bact&#233;ries ana&#233;robies peuvent &#233;galement se d&#233;velopper dans les zones inf&#233;rieures de l&#8217;agar, appauvries en oxyg&#232;ne.
Ensemble, ces techniques constituent des outils essentiels pour l&#8217;isolement et la quantification des micro-organismes, facilitant leur &#233;tude dans les domaines de la recherche, de la clinique et de l&#8217;industrie.

Techniques d’isolement de cultures pures

Les micro-organismes sont r&#233;guli&#232;rement cultiv&#233;s en laboratoire &#224; l&#8217;aide de diverses techniques visant &#224; les isoler, les ...

Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Growth      

Croissance microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

microbial colony isolation methods

Microbial colony isolation methods are used to grow, separate, and count microorganisms in the laboratory. These techniques depend on placing microbes into a suitable growth medium under aseptic conditions, which help prevent contamination. The inoculum, or sample added to the medium, may be transferred directly or prepared as a diluted bacterial suspension.

The streak-plate method is a common way to obtain pure microbial colonies. In this method, a sample is spread across the agar surface in a step-by-step streaking pattern. Each new streak lowers the number of cells, so isolated organisms appear in the final streaked areas. After incubation, these cells grow into visible, discrete colonies that are useful for studying pure cultures and for later analyses.

The spread-plate method is used to measure the number of microorganisms in a suspension. A measured volume of the bacterial suspension is spread evenly over solidified agar with a sterile spreader, such as a glass or metal rod. After incubation, colonies form on the surface. By counting the colonies and using the dilution of the inoculum, the concentration of viable microorganisms in the original sample can be calculated.

The pour-plate method also supports microbial counting. In this technique, a measured bacterial suspension is mixed with molten agar that has cooled to about 45 to 50 degrees Celsius, then poured into a sterile petri dish. As the agar solidifies, some cells become embedded in the medium and others remain on the surface. After incubation, colonies grow in both locations. This method is useful for aerobic and microaerophilic bacteria, and anaerobic bacteria may also grow in the lower, oxygen-poor parts of the agar. Together, these methods are important tools for studying microorganisms in research, clinical, and industrial settings.

Microbial Colony Isolation Methods

binary fission

Bacterial Cell Division by Binary Fission

Binary fission is the main way prokaryotes, such as bacteria, reproduce asexually. It produces two daughter cells that are genetically identical. When conditions are favorable, this process helps bacterial populations grow quickly. The process starts when the bacterial chromosome is copied. The circular DNA unwinds at a specific origin of replication called oriC. DNA polymerases then build matching strands in both directions until replication reaches the terminus. This creates two identical...

generation time

Bacterial Doubling Time

Bacterial generation time is the time needed for a bacterial population to double during exponential growth. It is a useful measure of microbial growth under optimal conditions. The rate can vary a lot from one species to another, and it can be affected by temperature, pH, and nutrient availability. Some bacteria grow quickly, while others grow much more slowly. Escherichia coli can have a generation time of about 20 minutes. Mycobacterium tuberculosis has a much longer doubling time, often 12...

bacterial growth curve

Stages of Bacterial Population Growth

Bacterial population growth in a closed system follows a set pattern called the bacterial growth curve. It describes how a bacterial population changes when temperature and nutrient levels are controlled. The curve has four phases: lag, log, stationary, and death. The lag phase is the first stage. During this time, bacteria adjust to their new environment. They make enzymes and other needed molecules for cell division, but the number of cells changes very little. This step prepares the...

microbial growth measurement: direct methods

microbial-growth-measurement-direct-methods

Counting Microbes with Direct Methods

Counting microbes with direct methods gives a fast way to measure how many cells are in a culture. In microbiology, these methods provide quantitative data for research and diagnostics. The main approaches are microscopic counts, plate counts, and serial dilution. Microscopic counting uses a Petroff-Hausser chamber, which is a special microscope slide with a grid and a known depth. A liquid culture is viewed under the microscope, and the cells in the grid are counted to estimate cell density...

microbial growth measurement: indirect methods

microbial-growth-measurement-indirect-methods

Measuring Microbial Growth Without Counting

Measuring microbial growth with indirect methods helps scientists estimate population size without counting every cell. These methods track signs of growth such as turbidity, metabolic activity, and biomass. They are useful because they are efficient and can give reproducible results. Turbidity is one common approach. During exponential growth, microbial cells scatter light in proportion to their biomass. A spectrophotometer measures this as optical density, or OD, also called absorbance.

microbial growth media

Selecting Microbial Growth Media

Microbial growth media give microorganisms the nutrients and conditions they need to grow in the lab. These media let scientists study microbial physiology, behavior, and interactions. Choosing the right medium is important for research, diagnosis, food safety, and environmental studies. Growth media can be solid, liquid, or semisolid. Solid media, often made with agar, support visible colony growth so microbes can be isolated and counted. Liquid media support even growth throughout the tube...

need for obtaining pure cultures

Isolating and Preserving Pure Cultures

Pure cultures are single microorganism species grown apart from mixed samples. They help scientists study microbes with the same genetic and physical traits under controlled conditions. This makes pure cultures important in microbiology research and in many real-world uses. To obtain a pure culture, a single microbial type must first be separated from a mixed population. Common methods include serial dilution, streak plating, pour plating, and spread plating. The chosen sample is then placed...

techniques for isolation of pure cultures

Microbial colony isolation methods are used to grow, separate, and count microorganisms in the laboratory. These techniques depend on placing microbes into a suitable growth medium under aseptic conditions, which help prevent contamination. The inoculum, or sample added to the medium, may be transferred directly or prepared as a diluted bacterial suspension. The streak-plate method is a common way to obtain pure microbial colonies. In this method, a sample is spread across the agar surface in...

factors influencing microbial growth: ph

Microbial pH Preferences and Growth Adaptation

Microbial growth depends on pH, the measure of how acidic or alkaline an environment is. Different microorganisms grow best in different pH ranges. Their ability to keep a stable internal pH helps protect enzymes and other macromolecules. External pH changes can challenge that balance. Neutrophiles grow best near neutral pH, usually between 5.5 and 8.0. Escherichia coli is a common example. These microbes often live in neutral or slightly acidic places. They can use potassium-proton exchange...

factors influencing microbial growth: temperature

factors-influencing-microbial-growth-temperature

Microbial Growth at Different Temperatures

Temperature shapes microbial growth by changing enzyme activity, membrane fluidity, and other cell processes. Each microorganism has a minimum, optimum, and maximum temperature range. Below the minimum, membranes lose fluidity and transport stops. Above the maximum, proteins denature and membranes break down. At the optimum temperature, enzyme reactions run fastest and growth is highest. Microorganisms are grouped by the temperatures they prefer. Psychrophiles grow in cold environments from...

factors influencing microbial growth: osmolarity

factors-influencing-microbial-growth-osmolarity

Microbes and Water Availability in Salty Environments

Microbes and water availability in salty environments are closely linked to osmolarity, which is the measure of solute concentration in a solution. Osmolarity helps determine how much water is available for living things. Water moves across semipermeable membranes by osmosis. It flows from a more dilute area to a more concentrated one. When the outside environment has a high solute level, microbial cells lose water. This can cause dehydration and slow or stop growth. The amount of water...

oxygen requirements and growth patterns

Microbial Oxygen Needs and Tolerance

Microbial oxygen needs and tolerance shape how bacteria grow and survive. Oxygen can support energy production in some microorganisms, but it can also become harmful in certain environments. These differences help explain why microbes live in very specific places. Microorganisms are grouped by how they use oxygen. Obligate aerobes, such as Mycobacterium tuberculosis, need oxygen because it serves as the terminal electron acceptor in aerobic respiration. Obligate anaerobes, such as Clostridium...

biofilms

Biofilm Growth and Surface Attachment

Biofilms are communities of microorganisms that attach to a surface and build a self-made sticky matrix around themselves. This matrix is made of extracellular polysaccharides, which are sugar-based substances secreted by the cells. Biofilms may contain one species or several species, and their organized layers help the microbes survive better together. Biofilm formation happens in four main stages: attachment, colonization, development, and dispersal. In the first stage, free-swimming...

key terms and concepts

Learn how streak-plate, spread-plate, and pour-plate methods isolate or count microorganisms on agar using aseptic lab techniques and incubation.

Microbial Colony Isolation Methods | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

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BIO.4.a

Binary Fission

Binary fission is the primary mode of asexual reproduction in prokaryotes, such as bacteria. It results in the production of two genetically identical ...

Generation Time

Bacterial generation time, the period required for a bacterial population to double during its exponential growth phase, serves as a critical measure of ...

Bacterial Growth Curve

The bacterial growth curve is a fundamental concept in microbiology that describes the dynamics of bacterial population growth in a closed system with ...

Microbial Growth Measurement: Direct Methods

Direct methods for measuring microbial populations in a culture are essential tools in microbiology, providing quantitative data for various applications. ...

Microbial Growth Measurement: Indirect Methods

Estimating microbial growth is essential for understanding population dynamics and environmental adaptations. Indirect methods provide valuable insights ...

Microbial Growth Media

Microbial growth media are essential tools in microbiology, providing the nutrients and conditions necessary to cultivate and study microorganisms. These ...

Need for Obtaining Pure Cultures

Pure cultures, defined as the growth of a single microorganism species isolated from mixed populations, are fundamental tools in microbiological research ...

Microorganisms are routinely cultured in the laboratory using various techniques to isolate, grow, and quantify them for further study. These methods rely ...

Factors Influencing Microbial Growth: pH

Microorganisms are classified as acidophiles, neutrophiles, or alkaliphiles based on their pH growth preferences, reflecting their adaptations to specific ...

Factors Influencing Microbial Growth: Temperature

Microorganisms display remarkable adaptations, enabling them to thrive in diverse ecological niches across a wide range of temperatures. Temperature ...

Factors Influencing Microbial Growth: Osmolarity

Osmolarity is the measure of solute concentration in a solution. It plays a critical role in determining water availability for organisms. Water moves ...

Oxygen Requirements and Growth Patterns

Microorganisms exhibit diverse oxygen requirements and growth patterns driven by their metabolic strategies and environmental adaptations. Oxygen, while ...

Biofilms

Biofilms are complex communities of microorganisms encased in a self-produced extracellular polysaccharide matrix attached to surfaces. These microbial ...

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Prokaryotic vs. Eukaryotic Cells

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Microbial Morphologies 

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Bacterial Cell Wall 

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Archaeal Cell Wall

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Peptidoglycan Synthesis

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Plasma Membrane in Bacteria and Archaea

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Outer Layers of the Cell Envelope

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Cell Inclusions

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Endospores and Sporulation

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Nucleoid

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Surface Appendages of Archaea

Archaeal surface appendages are highly specialized structures essential for environmental adaptation, encompassing roles in adhesion, biofilm formation, ...

The student will investigate and understand that bacteria and viruses have an effect on living systems. Key ideas include  the structures and functions can be compared

BIO.4.c

Types of Microorganisms

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environmental-applications-of-microorganisms

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Quantifying Environmental Microorganisms and Viruses Using qPCR

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Culturing and Enumerating Bacteria from Soil Samples

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Bacterial Growth Curve Analysis and its Environmental Applications

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BIO.4.d

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Defense Mechanism Against Infection

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The student will investigate and understand that bacteria and viruses have an effect on living systems. Key ideas include  the germ theory of infectious disease is supported by evidence.

BIO.4.e

Microbial Colony Isolation Methods

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