· Antibiotics are the chemical substances produced by or derived from microorganisms (bacteria or fungi), which kill or suppress the growth of other microorganisms at very low concentrations.
· The first antibiotic, Penicillin was discovered by Eminent British Bacteriologist, Sir Alexander Fleming in 1928 AD.
· He was doing research on Staphylococcus (bacteria). One day, he saw some spores of mould growing in his laboratory. While throwing the moulds out of the window, one of the moulds landed on one of his Staphylococcus colonies. He observed that these bacteria were quickly destroyed.
· He came to the conclusion that moulds had some characteristics that inhibited the growth of Staphylococcus. The mould was identified as Penicillin notatum and the active substance was therefore named Penicillin.
· But until 1941AD, Penicillin was not purified and used for clinical purposes.
· Chloramphenicol is the first completely synthetic antibiotic to be produced commercially.
· Bacteria are prokaryotes. Most of them are free-living, some are parasites or commensals and some others are pathogens to humans and plants. They cause diseases either by directly invading the cells or by producing poisonous chemicals called ‘toxins’. The toxins rapidly damage the cells. Invaded bacteria use the cell nutrients and multiply too fast.

Some common Bacterial Diseases in Human
Disease Pathogen (Causative agent)
Tuberculosis Mycobacterium tuberculosis
Typhoid Salmonella typhi
Cholera Vibrio cholera
Tetanus Clostridium tetani
Pneumonia Diplococcus pneumonia
Whooping cough
Bordetella pertussis
Syphilis Treponema pallidum
Diptheria Corynebacterium diphtheria
Plague Yersinia pestis
Leprosy Mycobacterium leprae

General Features of Antibiotics

a. They are biologically active against a large number of organisms even in extremely low concentrations.
b. They kill or inhibit the growth of pathogens but not the host cell.
· This is because antibiotics could only bind the 70S ribosome of bacteria, inhibiting protein synthesis and thus killing them, leaving the host cell undamaged. They act selectively too.
· For example, Penicillin acts on gram-positive bacteria (e.g. Streptococci) and Streptomycin acts against gram-negative bacteria (e.g. Escherichia coli).
cRange of the effectiveness of antibiotics may be narrow-spectrum or broad-spectrum.
· Broad-spectrum type act on a large number of related and non-related bacteria (e.g. Chloramphenicol and Tetracycline) and narrow-spectrum act on a limited variety of bacteria (For example, Isoniazid, Amoxycillin, Penicillin).
d. Nowadays, some semi-synthetic antibiotics are also produced (e.g. Ampicillin and Methicillin) by the technical modifications of natural antibiotics by the addition of extra chemicals so that it is not activated by pathogens.

Mechanism of Action of Antibiotics
· Administration of antibiotics causes the death of microorganisms. Antibiotics disrupt a vital link in the metabolism of pathogens like a synthesis of enzymes, destruction of a cell wall, alternate membrane function, inhibit protein synthesis, inhibit the production of nucleic acids etc.

· Bacterium, exposed to Penicillin, can’t divide. Penicillin is bactericidal. It interferes with the chemicals needed by the bacterium to form its cell wall. This causes the cell wall to disintegrate and the bacterium dies. Similarly, Polymyxin disrupts the cell wall and the permeability of bacterium. Antibiotics like Streptomycin, Erythromycin, Chloramphenicol and Gentamycin inhibit protein synthesis.

· Antibiotics with their modifications are used as medical preparations to cure some diseases such as TB, Plague, Cholera, Pneumonia etc. which were previously considered incurable.

Types of Antibiotics
· On the basis of action against micro-organisms, antibiotics are of two types:
a. Bacteriostatic (that inhibit the further growth of the bacteria) &
b. Bactericidal (that kill bacteria)

A. Bacteriostatic antibiotics are:
    1. Chloramphenicol
    2. Tetracycline
    3. Bacitracin
B. Bactericidal antibiotics are:
    1. Amoxycillin
    2. Penicillin
    3. Cephalosporin
    4. Polymyxin
    5. Colistin

Application of Antibiotics
1. Antibiotics are generally used to treat and control many bacterial diseases and have contributed to the maintenance of human health.
2. Antibiotics are also used in the preservation of food especially fresh meat, fish, poultry feed etc.
3. Livestock animals are given large quantities of antibiotics in the feed to promote the growth of the animals.
4. Antibiotics are also used for the treatment of diseases in plants.


· Vaccines are the liquid chemical substances prepared from weakened (attenuated) or dead pathogens or their antigens which are administered orally or injected into the body to stimulate the host’s immune system by inducing antibodies formation.
· Vaccination is the process of administering preparations of live attenuated (weakened) or killed microorganisms or their products to an individual in order to develop active immunity.
· Vaccination enables us to fight against external infections.
· Immunization is the process by which the body produces antibodies against vaccine-preventable diseases through the administration of specific vaccines.
· These are used to protect ourselves and our domestic animals against bacterial and viral diseases.
· Edward Jenner in 1796AD observed that milkmaid who has contracted cowpox did not get smallpox which led him to discover the practice of vaccination against smallpox.
· The term vaccine was coined by Louis Pasteur on July 6, 1885 A.D.
· An antigen is a foreign molecule (macromolecule), usually a protein that stimulates the production of antibodies (an immunoglobulin) when introduced into the body of a living organism.
· Antibody is the protein developed in the body against the toxic chemicals produced by pathogens. It is produced by lymphocytes (WBCs).

Antigens Antibodies
These are foreign molecules. They are self-molecules and circulate in the body fluid.
Chemically they are either proteins or polysaccharides or lipoproteins. Chemically they are always proteins.
Their entry into the body provokes the formation of antibodies. They are produced in response to the antigens in the host’s body.
They cause disease or auto-immune disease. They protect the body against pathogens (bacteria and viruses).

Immunity and its Types
· Immunity is the ability of a body to fight against pathogens.
· WBCs make the immune system of the body.
· It can be achieved in two types:
1. Natural (Inborn or non-specific) immunity
2. Acquired or specific immunity

1. Natural Immunity
· This type of immunity is present since birth.
· During embryonic development, some antibodies from the placenta of the mother pass to the foetus.
· They protect the young ones from measles and polio.
· However, this immunity is short-lived.

2. Acquired immunity
· This immunity is acquired after birth.
· It may be active or passive.
a. Active immunity
· It is produced by injecting a small quantity of an antigen called a vaccine into the body, by vaccination.
· The body manufactures antibodies against the antigen so active immunity lasts for a long time.
· Vaccines for TB, diphtheria, whooping cough, cholera, tetanus, typhoid, mumps, measles, yellow fever, smallpox provide active immunity.

b. Passive immunity
· In this immunity, the body does not produce antibodies instead the readymade antibodies from some other animals are introduced to the person for the protection against a particular disease.
· The effects are for a short period and temporary.
· For example; antivenin provides passive immunity against snake venom.

Types of Vaccines

· On the basis of the mode of introducing the infectious organism in the body without infecting it, vaccines are of the following types:
a. Killed or inactivated vaccines
· These vaccines are prepared by killing the pathogenic organisms by heat or UV rays or alcohol or formalin or phenol.
· For example, typhoid vaccine, cholera vaccine, rabies vaccine, plagues vaccine etc.

b. Toxoids
· These vaccines are prepared by detoxifying the toxins produced by certain organisms but retaining their antigenic property.
· For example, Diptheria and Tetanus toxoid.
· These vaccines provide immunity for short period.
· These vaccines provoke the formation of protective antibodies.

c. Live or Attenuated vaccines
· The pathogen is made weakened to make it non-virulent.
· For example, Oral Polio Vaccine (OPV), Bacillus Calmette Guerin (BCG), Smallpox, Yellow fever, Mumps, Measles, Rubella (MMR) provide life-long immunity.
· The live pathogens are identical to the disease-causing pathogens in their antigenic profile, but they lack the ability to cause the disease.

d. Combinations
· If more than one kind of immunizing agent is included in the vaccine, it is called combined or mixed vaccine.
· For example: DPT (Diptheria+ Pertusis+ Tetanus), DT (Diptheria + Tetanus), MMR (Measles+ Mumps + Rubella) etc.

Applications of vaccines
· The applications of vaccines are listed below:
1. Vaccines reduce the burden of many bacterial and viral diseases. 
They develop immunity against infectious diseases.
2. Vaccines are used to destroy or kill disease-causing organisms.

Name of vaccine Category of vaccine Used in the treatment of
Diptheria Toxoid Diptheria, Whooping cough and Tetanus, Often given in a single preparation (DPT, the triple vaccine)
Pertussis Killed bacteria Diptheria, Whooping cough and Tetanus, Often given in a single preparation (DPT, the triple vaccine)
Tetanus ToxoidDiptheria, Whooping cough and Tetanus, Often given in a single preparation (DPT, the triple vaccine)
Oral Poilo vaccine (OPV) Live vaccine Polio
Measles Attenuated vaccine (Virus) Measles, Mumps and German Measles and smallpox, Often given as a mixture (MMR)
Mumps Attenuated vaccine (Virus) Measles, Mumps and German Measles and smallpox, Often given as a mixture (MMR)
Rubella Attenuated vaccine (Virus) Measles, Mumps and German Measles and smallpox, Often given as a mixture (MMR)
Chickenpox Attenuated vaccine (Virus) Chickenpox
Rabies Inactivated vaccine (Virus) Rabies
Smallpox Attenuated vaccine (Virus) Smallpox
To protect against a possible bioterrorist attack
Tuberculosis Attenuated vaccine (BCG) Tuberculosis

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