PRINCIPLES AND TECHNIQUES OF EMPLOYING MICROORGANISMS FOR THE
QUALITATIVE ASSAY OF PRODUCTS (Antibiotics, Amino Acids and Vitamins)
Introduction
Microorganisms are highly sensitive to many biologically active substances such as antibiotics,
amino acids and vitamins. Because of this sensitivity, they are widely used as biological indicators
for detecting, identifying and measuring the presence of these substances in pharmaceutical and
biological samples.
A microbial assay is a method in which the response of a microorganism is used to detect or
estimate the presence, absence or potency of a substance.
These assays may be:
• Qualitative – to determine presence or absence
• Quantitative – to measure the amount or potency
This lecture focuses on qualitative assays.
Principle of Microbial Assay
The basic principle is that: Certain microorganisms require specific nutrients for growth or are
inhibited by certain chemicals. The response of the microorganism indicates the presence of the
substance.
Two major biological responses are used:
1. Growth promotion – used for vitamins and amino acids
2. Growth inhibition – used for antibiotics
Why Microorganisms are Used
Microorganisms are ideal assay tools because they:
• Are highly sensitive
• Give reproducible results
• Respond only to biologically active substances
• Are inexpensive and easy to maintain
• Can detect substances in very small concentrations
Types of Microbial Qualitative Assays
Substance Microbial response Type of assay
Antibiotics Inhibition of growth Inhibition assay
Vitamins Stimulation of growth Growth response assay
Amino acids Stimulation of growth Growth response assay
QUALITATIVE ASSAY OF PRODUCTS (Antibiotics, Amino Acids and Vitamins)
Introduction
Microorganisms are highly sensitive to many biologically active substances such as antibiotics,
amino acids and vitamins. Because of this sensitivity, they are widely used as biological indicators
for detecting, identifying and measuring the presence of these substances in pharmaceutical and
biological samples.
A microbial assay is a method in which the response of a microorganism is used to detect or
estimate the presence, absence or potency of a substance.
These assays may be:
• Qualitative – to determine presence or absence
• Quantitative – to measure the amount or potency
This lecture focuses on qualitative assays.
Principle of Microbial Assay
The basic principle is that: Certain microorganisms require specific nutrients for growth or are
inhibited by certain chemicals. The response of the microorganism indicates the presence of the
substance.
Two major biological responses are used:
1. Growth promotion – used for vitamins and amino acids
2. Growth inhibition – used for antibiotics
Why Microorganisms are Used
Microorganisms are ideal assay tools because they:
• Are highly sensitive
• Give reproducible results
• Respond only to biologically active substances
• Are inexpensive and easy to maintain
• Can detect substances in very small concentrations
Types of Microbial Qualitative Assays
Substance Microbial response Type of assay
Antibiotics Inhibition of growth Inhibition assay
Vitamins Stimulation of growth Growth response assay
Amino acids Stimulation of growth Growth response assay
