Introduction:

Biological assays or bioassays are scientific experiments utilized to test effects of the compound on living organism, and are necessary in drug developments and monitoring of environmental pollutants. Sensitivity tests are laboratory methods utilized to find out vulnerability of microorganisms to drug therapy.

Drug Bioassays:

Many drugs are isolated from natural products, and consequently pharmacological screening or evaluation is essential to guide isolation procedure towards production of the pure active bio-component. Bioassays find out concentration of purity or biological activity of substances like hormones and plant extracts, whereas measuring effects on the organism or tissue cells compared to the standard preparation. The objectives of drug bioassays are; measurement of pharmacological activities of new or chemically undefined compounds, investigating functions of endogenous mediators, to know side effects of drug to be used, and concentration measurement of known substances. Drug bioassays are generally quantitative, in that they compute biological response evoked by the use of such drugs, and they are generally analyzed using biostatistics. The drug bioassay may be primary or secondary assay depending on specific criteria like cost and duration of results. The primary bioassay may not be quantitative, and is applied to the large number of samples; it is cheap and generates results rapidly. While secondary bioassays are applied to more thorough samples, are slow and costly. The primary bioassay must meet certain criteria like:

• Its results must be able to forecast therapeutic potential of substance being tested either directly or indirectly by comparing with other known effective drugs which have been screened through same process
• The potentially helpful pharmacological activity must not go hidden even although the activity may be unexpected or unique
• The probable nature of the activity must be highlighted such that subsequent research can be performed intelligently
• The bioassay must be tolerant of several impurities present in crude extract, but also be able to detect presence any interesting substances in low concentration
• The screen must permit use of both crude materials and pure isolates so that the procedures can be utilized to direct extraction, isolation and purification work of natural product chemist
• The procedure must not need expensive equipments or sophisticated laboratory environment so that primary level of screening experiment can be performed synchronously with fractionation process
• The procedure must be simple enough to be taught to laboratory technicians so that there would not be a need to involve highly trained and qualified researchers to run routine operation of bioassay program.
• Test animals, if needed for bioassays must be effortlessly available, simply bred, easily handled and resistant to infection

There are four approaches which act as bioassay guide in drug discovery research, and the choice of screening approach depends on target disease and available information about the target organism to be studied. The approaches are as follows:

i) Use of the single bioassay method to search for the specific kind of pharmacological activity like anti-inflammatory activity

ii) Use of specific bioassay method, with each procedure designed to capture specific helpful properties

iii) Use of single bioassay method to discover numerous activities

iv) Use of the variety of combination of bioassays to notice specific and numerous activities.

There are essentially two kinds of bioassays; Quantal and Graded. The quantal bioassay needs all or none response that has no room for intermediate results. In case of toxicity studies, animal receiving drug either dies or not. Graded bioassay is based on the observation that, balanced increase in dose levels causes a similar increase in response. Methods involved in determination of bioassays are:

i) Matching bioassays: Simplest kind of bioassay and it involves taking the response of first substance and then matching it with standard response. This technique is applied to small sample sizes and major limitation is that it doesn't take into consideration sensitivity of drug; therefore it is not precise or reliable.

ii) Interpolation method: This is performed by finding amount of preparation of unknown potency needed to produce the definite effect on appropriate tissues or test animals under the standard condition, and effect is compared to standard.

Drug Sensitivity Tests:

When the microorganism has been recovered from the clinical specimen, it is cultured and tested against the variety of drugs. If the growth of the microbe is reserved by action of the drug, it is reported as being responsive to the drug, but if actions of the drug have little or no effect on the development of the microbe, the microbe is reported to be resistant to the drug. This procedure is called as drug sensitivity test, and culture utilized in this test is dependent on kind of microorganism. Drug sensitivity tests assists to give information about strength of certain drugs, if they are still efficient and to what extent if they are. Without drug sensitivity tests, drugs are prescribed on the trial and error basis, that could take several days for the observed improvement and at times may lead to numerous complications during course of illness like kidney impairment, or even lead to death of patients. Culturing microorganisms before testing for drug sensitivity is done to allow reproduction and development of the microbe for simple identification of results. It generally takes up to 18 hours to get results for bacteria, but it could take numerous weeks to examine colonies in bacterium which causes tuberculosis. Culture mediums are generally sterile plastic dishes having nutrient gel on which they feed, and at times substances are added to medium to suppress the development of other bacteria not required. Though, viruses need living cells to grow. After culturing, the small portion of colony is removed and stained for proper recognition under microscope. Once properly recognized, drug sensitivity test is performed by inserting paper discs having drugs of specification, in bacteria culture medium. Medium is checked after 24 hours to examine the drug which bacterium is most sensitive to.

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