Microbial | Microbiological assay: Its Definition Uses and methods

Microbial assays or microbiological assays is a type of bioassay and are designed to analyse the compounds or substances which have effect on micro-organisms.

Microbial assay Definition: Microbiological assay is defined as the determination or estimation of concentration or potency of an antibiotic by means of measuring and comparing the area of zone of inhibition or turbidity produced by test substance with that of standard over a suitable microbe under standard conditions.

Hypothesis: So as definition says the hypothesis is that when an antibiotic is administered, there is inhibition in the growth of microbe as indicated by decrease in area of zone of microbial colony on nutrition media or decrease in turbidity due to decrease in microbial concentration.

Uses of microbial assay:

1. They help to estimate concentration and potency of anti-biotics. This is not always possible by other means of estimations.

2. Help in determination of the best anti-biotic suitable for patient recovery. When microbe in patients phlegm or urine is examined by biosaay, the better susceptibility of microbe to the suitable anti-biotic among those available to treat can be decided for proper treatment of infected patient. This determination is possible by immune assays like ELISA test for some diseases.

Basically there are two methods of microbiological assays

1. Agar Plate method

2. Turbidometric method

Agar Plate method : In this method the specified microbes are suspended in suitable nutrition media. The this nutrition media with microbes is poured into a petri-dish and allowed to incubate at suitable temperature. This supports the growth of microbes exponentially.

The suitably cut circular filter paper pieces are immersed in the anti-biotic solutions of both test and standard. Then the pieces are placed on the microbial nutritional media all over with suitable gaps in between and incubated again.

After specified time of incubation the plates are removed and the diameter of the zone of inhibitions of test and standard samples are measured.

By comparing the areas of zone of inhibition of test with standard the concentration and potency of test samples are determined.

Here the specified microbe is grown in a liquid form of nutrition media. Then the seeded media transferred into various test tubes required to be assigned into groups for standard and test samples evaluation.

Then different dilutions of test and suitable dilution of standard are taken for estimation into the microbe seeded media present in the test-tubes. After incubation at proper temperature for specified time the microbial growth inhibition of both test and standard samples are evaluated.

This is done by measuring the turbidity of the media in different test-tubes using either turbidometer if highly viscous or nephleometry if dilute.

The remaining process of comparison and estimation of concentration or potency is same as plate method.

This is the brief introduction to the microbial assay definition, uses and methods.

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