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Renin Angiotensin Mechanism.

Microbiological Assay: Introduction

 

Introduction:

  • The microbiological or microbial assay is a type of biological assay in which the relative potency of activity of a compound is determined by measuring the amount required for producing the predicted effect on a suitable test organism under standard conditions. 

  • The principles involved in microbial assays are similar to those applied to assays or higher plants or animals. 

  • The microbiological assay is a biological assay performed using microorganisms, e-g. bacteria, yeast, and moulds. 

  • These assays are much easier than those performed using mammals for isolating essential vitamins; for example, a growth factor for Lactobacillus proved to be similar to a haematopoietic factor in pernicious anemia patients. 

  • Many therapeutic agents, such as antibiotics inhibiting microbial growth or the essential growth factors (vitamins and amino acids), are standardised by microbiological assays. 

  • The activity of antibiotics, vitamins, or amino acids is determined by microbiological assays; while the potency (concentration or amount) of such substances is determined by chemical assays. 

  • Thus, microbiological assays of antibiotics, vitamins, and amino acids are significantly important.  

Principles

  • A microbiological assay relies on the principle that when certain compounds are present in limited amounts, the amount of microbial growth corresponds to the amount of these compounds. 

  • The basic procedure of most of the microbial assays is the same; however, the test conditions vary. 

  • The test substance is added to a liquid or gel medium, test microorganism is inoculated on the medium, and the resultant response (which depends on the substance's biochemical effect on the test organism) is observed. 

  • It may be a growth response (positive in the assay of nutrients and negative in the assay of antibiotics), which is determined by counting, optical density, weight, or area; the growth response may be a definite end-point, or an all-or-none response.  

Advantages of Microbial Assay:

  1. It is suitably used for compounds which cannot be assayed by either physical or chemical methods.

  2. It is used for the assay of naturally occurring therapeutic agents.

  3. It minimises the mortality rate of animals.

  4. It is a simple and rapid method as compared to bioassays.

  5. It is used for accurate standardisation of medicinal compounds.

  6. It determines the concentration as well as activity of compounds.

  7. It does not require a large amount of samples and instruments.

  8. Its complete procedure can be automated to minimise the duration. 

Disadvantages of Microbial Assay:

  1. lt requires a specific test organism for the assay of a particular compound.

  2. It demands maintenance of sterile conditions within the laboratory.

  3. It may give invalid results due to a slight variation in incubation temperature.

  4. It is a time-consuming method.

  5. It requires well trained and expert individuals
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