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What is a Pure Culture?

The environment around us consists of a mixed population of microbes. Each of these groups of organisms contributes to the ecology. However, ever wondered how are the studies carried on such microbes? Is it feasible to study and experiment with all of these together? Well, no. It isn’t. To carry out the studies on these microbes, it is essential to dissect the mixed culture into a pure culture. 

Now, what is a pure culture? What purpose does it serve? What is pure culture microbiology? What are the pure culture methods or pure culture techniques?  Let us help you understand all these terms in detail.


Pure Culture Definition

Put down in simple terms, pure culture is defined as a laboratory culture that contains just one species of organisms in microbiology. Microbes are usually in mixed cultures. But, the pure culture can be derived from it through the transfer of a bit of its sample in the new and sterile growth medium. 


The process of pure culture isolation usually takes place by the dispersion of cells across the surface medium. This mainly involves thinning of the sample before it is inoculated into a new medium. There are several pure culture techniques utilized by scientists to carry out the process of the creation of discrete colonies of pure microbes. 


The techniques of isolation of the pure culture were primarily developed by Robert Koch during the mid-19th century. Microbiologists of those times readily adopted these methods for the production of a single strain of the organism. 


The inculcation of such techniques of pure culture led to bacterias characterization that was responsible for causing anthrax, tuberculosis, and such major diseases. Following this, scientists developed similar procedures for protozoa, fungi, and algae. 


Are you wondering that do pure culture organisms serve any commercial purposes? Well, yes, they do. It is mainly used for commercial fermentation purposes including yoghurt, alcohol, citric, lactic acid, and several other beverages for many years now. The pure culture technique has also contributed to the development of several vaccines and antibiotics.


Pure Culture Collections:

These are a resource and method of preserving the genetic resources of these organisms. The collection of pure culture organisms varies widely depending on size and some specializations as well. These have gained importance over the years due to their authenticity, reliability, and practical uses. For culture, several national federations are present across various countries, and detailed information is available about the same.


How is the Purity of Culture assessed? 

The assessment of the purity of culture is carried out through different methods. These are as follows:

  • The same cultural characteristics are shown on the media obtained in the isolated colonies of pure culture organisms. 

  • The same culture organisms look alike when observed under the microorganisms. This means that they get the same stain and have the same morphology. 

  • Just like similar biochemical results the isolated colonies of pure culture perform identically, i.e., separately.

Biochemical Characteristics of Pure Culture

  • The mixed culture organisms show different results in the case of experiments. 

  • The pure culture organisms show similar results in the case of experiments.

What is the Importance of Pure Culture in Microbiology?

  • The organisms of pure culture can be grown, tested, characterized, and identified. 

  • It is feasible to study the clinical aspects and physiology of pure culture organisms. 

  • Irrespective of the number of times the test is done, the same results will be obtained for a particular culture of organisms during any sort of test. 

  • Spontaneous mutation occurs slowly in the case of pure culture, and the clone so formed is identical in all forms and aspects.

Pure Culture Techniques Microbiology

The various techniques used to obtain pure culture in microbiology are as follows:

  • Sterilization process for media and glassware

  • Dispersion of individual cells takes place across the medium

  • The thinning process of samples is carried out multiple times before the inoculation of fresh media takes place.

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FAQs on Pure Culture

1. What are the Sterilization Techniques Involved in Pure Culture?

The various types of sterilization techniques involved while carrying out the process of pure culture in microbiology are as follows:

  • Sterilization with moist heat

  • Sterilization with dry heat

  • Filtration

  • Sterilization using flame

  • Biosafety cabinets for laminar airflow

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2. What are the Isolation Methods for Pure Culture?

The isolation of pure culture can be done in the following ways.

  • Techniques of streak plate- This approach is most typically used to isolate pure bacterium cultures. A tiny amount of mixed culture is streaked across the surface of the agar medium with the tip of an inoculation loop/needle. The inoculum is suitably thinned out by successive streaks, and the microorganisms are separated from one another.
    Without reinoculation, it's usually best to streak out a second plate using the same loop/needle. These plates are incubated to allow colonies to grow. The basic premise of this method is that as bacterial cells are deposited on the agar surface, streaking creates a dilution gradient across the face of the Petri plate.

  • Techniques of pour plate- Plates of diluted samples combined with melted agar media are used in this approach.  The fundamental idea is to dilute the inoculum in successive tubes containing liquefied agar media, allowing for the complete dissemination of bacterial cells throughout the medium.

The combined bacteria culture is diluted immediately in tubes with melted agar medium kept at 42-45°C (agar solidifies below 42°C). The bacteria and the melting media are thoroughly combined.

  • The technique of serial dilution- This method is frequently used to create pure cultures of microorganisms that have yet to be effectively cultivated on solid media and only grow in liquid media.
    In this method of dilution, a microbe that predominates in a mixed culture can be isolated in pure form. The inoculum is serially diluted in a sterile liquid medium, and aliquots of each successive dilution are injected into a large number of tubes of sterile liquid medium.

  • The technique of spread plate- The mixed culture or microorganisms are diluted in a succession of tubes holding sterile liquid, commonly water or physiological saline, rather than in melted agar media (as in the pour plate method).
    The diluted liquid is spread equally across the surface drop by drop on the centre of an agar plate with a sterilized bent-glass rod. The medium has begun to incubate.
    When colonies are grown on agar medium plates, it is discovered that some plates produce well-isolated colonies. 

  • Enrichment method- It's usually used to isolate microorganisms that are present in modest quantities or grow slowly compared to the other species in a mixed culture.
    By introducing a specific nutrient into the medium and altering the physical conditions of the incubation, the enrichment culture technique creates a carefully designed cultural environment.

3. What are the Various Conditions Which Affect the Sample Culture?

The various conditions affecting the sample culture are listed below:

  • Water

  • Nutrients

  • Oxygen

  • Temperature

  • Acidity

  • pH

  • Chemicals

  • Light

All the conditions mentioned above should be studied thoroughly by the students and know what is the effect of each of them on the sample culture. Vedantu's study material provides complete knowledge to students and helps them get a complete detailed understanding of the various topics, this will help the candidates to prepare themselves for any type of questions that are asked in the examination form this topic. Also, students can solve the question papers provided by Vedantu that will help them to know their level of preparation. 

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