Primary and Secondary Screening

Primary Screening can be referred to as the isolation and detection of important industrial “microorganisms” from the ‘mixed population’ with the help of simple techniques. In this screening technique, very simple methods are used for detecting the micro-organism that is based on the biochemical characters of the microbes. However, the sample is isolated, serially diluted, and collected on an agar medium with the help of a specific technique and it also contains “pH Indicator Dye”. 

Secondary screening can be referred to as the characterization of the micro-organisms that are isolated and detected in primary screening with help of high procedures. 

Primary and Secondary Screening of Microorganisms: Differences

Along with the help of primary screening, only basic information of isolated areas can be generated. Therefore, in secondary screening full details of the isolated colony is obtained and determined that it is capable of being used on an industrial scale. It is a screening method that can give a high yield of selective products with the help of low-cost raw material. Along with the help of both of these methods a microorganism can be determined and used in industrial fermentations for producing human utility compounds. The primary screening is used for conducting various types of cells, tests, assays or in some research programmes. The primary screening method is generally used for isolating and detecting a selected organism and determining that it can produce the compound without adopting many ideas or not. However, primary screening does not provide the idea that which “organic acid” has been produced. Primary screening helps to determine the microorganisms and organic acid in cells and other desired organisms. 

Secondary screening can be used for determining the quantitative and qualitative information about the cells, desired organisms or strains. In the case of qualitative screening, it can help to determine the yield potential and antibiotics of a product. However, in the case of quantitative screening, it can help to determine the product’s quantity that is obtained by various types of fermentation media. There are various types of techniques used in secondary screening that are useful in determining the production of a product. Along with the help of secondary screening, necessary information of a product or desired organism can be identified and classified. It is also a helpful process of determining the “genetic instability of strain“. It is a very useful process that also helps to determine various types of nutrients in products and test the toxicity, which needs to be eliminated. Therefore, secondary screening also helps to study and determine the biological, chemical and physical properties of a selected product. 

Primary Screening and Secondary Screening Techniques 

There are some important techniques are used in primary screening which is discussed below:

The Crowded Plate Technique

This technique of primary screening helps to determine the microorganisms that are capable of producing the antibiotics or not. Along with the help of natural substrata such as soil or other sources that are composed the microorganisms. A “suitable aliquot” of “serial dilution” is chosen that can produce 300 to 400 colonies when it is plated on the agar plate, which is also called a crowded plate. 

Indicator Dye Technique

Along with the help of this method, the capability of producing amines or acids from natural sources through the product can be determined. Therefore, with the help of incorporating “pH indicator dyes” like bromothymol blue or neutral red into “nutrient agar medium” can be determined. In this indicator dye method, the calcium carbonate is incorporated into the section of the agar medium. Therefore, with the help of this method, the location of organic acid production can be indicated and those colonies are identified that are releasing organic acid. 

Enrichment Culture Technique

Generally, it is a method that helps to isolate the microorganisms that are the very low number in the sample of soil, which can possess the nutrient requirement that is very important in industrial usage. It can easily isolate the nutrients if required and incorporate them into a medium and also helps to adjust the incubation conditions. 

There are various types of secondary techniques that can help to determine important information about the product or microorganisms. The various types of secondary screening techniques are “Giant Colony Technique“, “Filtration Method“, “Liquid Medium Method“.

Giant Colony Technique

This method is used for determining the antibiotics that can be diffused using the solid medium. Streptomyces species are used in this method which is capable to produce the antibiotics at the time of primary screening.

Filtration Method

This is an important method that helps to test the poor antibiotics that are soluble in water and cannot be diffused through a solid medium. There are various types of dilutions of the antibiotics that are added and prepared to solidify and also to molten “agar plating medium”.

Liquid Medium Method

It is a different type of secondary screening method that helps to determine the actual number of produced antibiotic microorganisms such as Streptomyces. 

Conclusion 

Both of these primary and secondary methods are useful to determine the microbiology in a product or desired cells. Along with the help of the primary method, isolation and detection of microorganisms can be determined using the simple technique. Therefore, it can easily determine the biochemical characteristics that are presented in microbes and it is a very beneficial process. However, secondary screening can be used to determine all of the important information of the selected products or microorganisms.