Essay on Antibiotics | Organic Compounds

The below mentioned article provides an essay on antibiotics.

Organic compounds produced by fungi and other organisms, especially bacteria which inhibit the life processes of microorganisms are known as antibiotics. But Waksman (1947) defined antibiotics as organic compounds produced by micro­organisms, which in dilute concentrations have the capacity to inhibit the growth and even destroy other microorganisms.

Other workers in this field have sugges­ted that antimicrobial substances from higher forms of life, such as plants and animals should be included among the antibiotics. General usage of the term antibiotics actually applies to those organic compounds of fairly simple structure produced by organisms which inhibit growth of microorganisms.

In 1896, while investigating the cause of pellagra, Gosio isolated an acid crystal­line substance from moldy rice, which showed slight antibacterial activity. It appeared to be produced by the fungus Penicillium brevicompactum. Later it was also isolated from a number of other Penicillium species and was named mycophenolic acid.

It showed high activity against a large number of fungi, many of which are pathogenic to plants and humans, but it was much less active against bacteria. Mycophenolic acid was actually the first antibiotic to be isolated in a pure form.

During early twentieth century antibiotic activity of microorganisms was observed accidentally by various investigators.

Most famous of which is the one that led to the discovery of the antibacterial antibiotic penicillin. But during and shortly after the World War II it was realised that antibiotics could be of tremendous importance for human life. During that time screening of microorganisms producing antibiotics was started on a large scale by University laboratories and by the pharmaceutical industry.

The principal use of antibiotics is to control disease in man and animals. In addition to killing or inhibiting human and animal pathogenic organisms, an anti­biotic may also be useful for controlling plant diseases. Besides these, in recent times antibiotics are used in commercial scale for preservation of fruits, vegetables, poultry products, fish, etc.

Antibiotics are referred to specially as antibacterial, antifungal, and antiviral substances. The antibacterial antibiotics are much more widely known than the antifungal and antiviral antibiotics.

Some of the most common antibacterial antibio­tics are:

SFtreptomycin, Chloromycetin, aureomycin, terramycin, and neo­mycin.

Antibiotics are very specific in action. Penicillin, for example, is active against many Gram-positive bacteria and only a relatively few Gram-negative organisms. The occurrence of antibiotics is probably far more widespread than suspected at present. The largest source of antibiotics is, however, the Actinomycetes. The percentage of Streptomyces strains producing antibiotics is high.

To a comparatively much lesser extent, antibiotics are produced by fungi. Certain fungi produce substances which are capable of inactivating some of the plant viruses. The Basidiomycetes are especially noteworthy in this respect. Again extracts of Trichothecium roseum reduce infectivity of tobacco mosaic and tobacco necrosis viruses.

It is possible that one microorganism produces more than one antibiotic. Streptomyces griseus, for example, forms the antibacterial streptomycin as well as the antifungal antibiotics cyclohexJmide and candlcidin, and S. nmosus forms both the anti­bacterial oxytetracycline and the antifungal rimocidin.

On the other hand, the same antibiotic may be formed by various microorganisms, such as different species of one genus, or even species of several different genera. For example, the antibioticpatulin; which is formed by Penicillium patulum, P. expansum, P. claviforme, Aspergillus clavatus, A. terreus, A. giganteus, and by Gymnoascus spp.

Besides being widely used for controlling bacterial disease in man and animals, penicillin has been used successfully, to a limited extent, in controlling necrosis of giant cactus, caused by Erwinia carnegieana. Injections of penicillin into the necrotic tissue apparently diffuse through the plant tissues for some distance, kill the bacteria.

This is one of the new cases in which an antibiotic has been used successfully in therapeutic treatment of plant disease. This and similar other uses of antibiotics have opened up new approach of controlling plant diseases.

Up to the present, antifungal antibiotics have received considerably less attention than the antibiotic active against bacteria. In recent years, however, the interest in antifungal antibiotics has increased for various reasons.

The antifungal antibiotic cycloheximide, more commonly known under its brand name Actidione, was discovered 20 years ago. It is produced by S. griseus. Gycloheximide has also been isolated from S. noursei. It is toxic to a wide range of organisms, including yeasts, filamentous fungi, algae, protozoa, higher plants, and animals; but is inactive against bacteria.

It is a powerful antifungal agent, most fungi being affected at very low concentrations. Because of its higher activity against fungal plant pathogens and its systemic properties, numerous investigators have tested cycloheximide against a wide variety of fungal diseases in plants.

Griseofulvin in another antifungal antibiotic isolated from P. griseofulvin. Syno­nyms for griseofulvin are fulvicin, fulcin, and grisovin. It shows action against Basidiomycetes, Ascomycetes, Fungi Imperfecti, and certain Phycomycetes, causing stunting, excessive branching, abnormal swelling and distortion of hyphae. But its antifungal activity is rapidly lost in sunlight.

A highly antifungal group of antibiotic comprises of polyene macrolides produced by Streptomyces species. All known polyene macrolides possess a pronounced activity against yeasts and filamentous fungi. Polyene macrolides show high activity in vitro against a wide range of fungal plant pathogens.

They are, moreover, remar­kably non-toxic to host plants. The storage of dressed chicken can be prolonged by the use of this group of antibiotic. Several polyene macrolides have been used against mycoses in man.

The use of antifungal antibiotics in therapy of human mycoses has also received considerable attention. Of special interest in this respect is the antibiotic griseofulvin, which first was developed as a plant disease control agent, but which proved later of greater value as a chemotherapeutant of human fungal diseases of the skin, hair, and nails by oral application.

Griseofulvin is translocated in the human body without being toxic.

Some of the polyene macrolides, such as:

Nystatin, pimaricin, tricho- mycin, amphotericin B, and hamycin are of clinical use against diseases like moniliasis, vaginal candidiasis, coccidiomycosis, trichophytosis, and syste­mic mycosis.

True, most important antibiotics have been obtained from:

(i) The bacteria, and

(ii) The fungi.

But at least some have been reported from algae, lichens and seed plants.

Details of some of the common antibiotics are given below: