1. Laboratory Scale:

Soon after the discovery of use of a microorganism, the maxi­mum number of strains is searched and the most suitable strain is selected and multiplied. A laboratory scale apparatus/plant is manufactured. It has a glass fermentor (fermenter). All the parameters of the process are worked out like nutrients for the microbe, pH, aeration, disposal of C0₂ if evolved, optimum temperature, by products, product inhibition or stimu­lation, time of optimum production, separation of product and its purification. Ultimately, the laboratory scale process is finalised.

2. Pilot Plant Scale:

It is intermediate stage where working of the laboratory scale process is tested cost and qualities of the product are evaluated. Glass vessels are replaced by metallic containers. The container where fermentation is carried out is called bioreactor or fermentor. Aeration system, pH corrections and temperature adjustments are perfected.

3. Manufacturing Unit:

Its size is determined by the economics worked at during the pilot plant scale process. Bioreactor or fermentor is often large. Microorganisms are added in bioreactors in three ways:

(i) Support growth system or on surface of nutrient medium,

(ii) Suspended growth system or suspended in nutrient medium,

(iii) Column or immobilised growth system where microorganisms placed in calcium alginate beads are kept in columns.

Broad Spectrum Antibiotic. It is an antibiotic which can kill or destroy a number of pathogens that belong to different groups with different structure and wall composition. Specific Antibiotic. It is an antibiotic which is effective only against one type of pathogens.

Antibiotics function either as bactericides (killing bacteria) or bacteriostatic (inhibiting growth of bacteria). This is done by (i) Disruption of wall synthesis, e.g., peni­cillin, cephalosporins, bacitracin, (ii) Disruption of plasmalemma repair and synthesis, e.g., polymyxin, nystatin, amphotericin, (iii) Inhibition of 50 S ribosome function, e.g., erythro­mycin. (iv) inhibition of 30 S ribosome function, e.g., streptomycin, neomycin, (v) Inhibition of aa-tRNA binding to ribosome, e.g., tetracycline, (vi) Inhibition of translation, e.g., chloram­phenicol.

Characteristics of a Good Antibiotic:

(a) Harmless to host with no side effect,

(b) Harmless to normal microflora of alimentary canal,

(c) Ability to destroy pathogen as well as broad spectrum,

(d) Effective against all strains of pathogen,

(e) Quick action.

Resis­tance to antibiotics comes from (i) Development of copious mucilage, (ii) Alteration of cell membrane so that antibiotic cannot recognise the pathogen, (iii) Alteration of cell membrane which prevents antibiotic entry, (iv) Change to L-form by pathogen, (y) Mutation in patho­gen. (vi) Development of pathogen enzyme capable of modifying antibiotic.

Uses:

Antibiotics are used:

(i) As medicines for treatment of a number of pathogenic or infectious diseases. Because of antibiotics and their newer more potent forms, a number of formidable diseases are now curable, e.g., plague, typhoid, tuberculosis, whooping cough, diphtheria, leprosy, etc.

(ii) As preservatives in perishable fresh food articles (e.g., meat and fish), pasteurised and canned foods,

(iii) As feed supplement for animals, especially poultry birds because they enhance growth.

Chemicals, Enzymes and Other Bioactive Molecules:

Microbes are being used for commercial and industrial production of certain chemicals like organic acids, alcohols, enzymes and other bioactive molecules. Bioactive molecules are those molecules which are functional in living systems or can interact with their com­ponents. A number of them are obtained from microbes.

Organic Acids:

A number of organic acids are being manufactured with the help of microbes. The important ones are as follows: