Antibiotics are defined as the chemical substance which are produced by the different microoragnism like bacteria and fungi that can distroy or inhibiting the growth of microorganisms.Antibioticts stop the rapid growth of bacteria as well as other microorganisms and also kill them. Antibioticts directly targets on a cell of bacteria and distroy it.


In 1928,a Britist bacteriologist named Alexander Flemming discovered Penicillin,the world's first antibiotic.In fact,it was an accident.During that timre Flemming was working on Staphylococcus and it was a coincidence that some spores of a mould floated into his laboratory.He thought that it was nothing and threw out of his window. fig:Flemming

But it he found that is was distroying bacteria quickly and later on it was discovered as the penicillium notatum.It was the first antibiotic which killed bacteria and maned as penicillin.

Most commonly used antibiotics


It is the most commonly used antibiotic which was discovered for the first time in world in the history of antibiotics.It can b prepared by the help of penicilliumnotatum and Penicillium chrysegenum.It is highly effective for the treatment of bacterial diseases likeTetanus,pneumonia, syphills,etc.After its discovery,it has saved the life of millions of people.


It can be prepared from the mould such as Sterptomyces griseus.It is mostly used for the treatment of diseases like tuberculosis,influenza,etc.


It is a broad spectrum which is made up of group of antibiotics. It can cure many bacterial as well as viral infection.



Spectrum of activity


Ceohalosporium species

Gram positive bacteria



Gram positive and negative bacteria



Board spectrum

Penicillin G

Penicillium chrysogenum

Grem positive bacteria


Sterptomyces griseus

Gram negative bacteria

Table: List of important antibiotics

Action of antibiotics

Antibiotics are chemical substance which has anti-bacterial action. They are divided into two types on the basis of their action towards the bacteria. They are described below:

1. Bacteriostatic agent

They are the agent those stop the growth and development of bacteria inside the body as well as stop their multiplication. Some of its examples are chloramphenicol, erthromycin, tetracycline,etc. Such antibiotics cause following damage to bacteria:

  • By the process of lysis, it destroys the cell wall of the bacteria.
  • These antibiotics stop the growth and development of the bacteria..
  • These antibiotics bind theribosomes of the bacteria and affect the process of protein synthesis inside their body.
  • Some of the antibiotics does not kill the bacteria but control their reproduction.
  • Some of the antibiotics interferes in the process of nucleic acid formation and binds the DNA or RNA polymerase.

2. Bacteriocidal agent

These are the antibiotics which kills the microorganism. Some of it example are Penicillin, streptoymycin etc. Such antibiotics cause following effect to the microorganism:

On the basis of their effect, antibiotics are classified into two class:

  1. Board spectrum of antibodies: These types of antibiotics are highly effective to the different types of bacteria. These sorts of antibiotics show the highly effective actions towards the bacteria. Instead of stopping their activities these antibiotics directly destroy them.
  2. Narrow spectrum or specific antibiotics: These sorts of antibiotics have limited and specific function as well as show action on the few similar types of pathogens. The antibiotics which have specific functions towards the specific microorganisms are known as narrow spectrum antibiotics.

Q. Why antibiotics do not affect host cell?

= Antibiotics can treat the diseases only caused by the bacteria. They are able to do so, because they bind can the molecules that are found in the bacterial cell. They are unable to bind the molecules found in the host cell.

Difference between bacteriostatic agent and bactericidal agent

Bacteriostatic agent

Bactericidal agent

1. They take control over the growth and development of the bacteria.

2. They interfere in DNA or RNA replication.

3.For example; tetracyclin, erythromycin, etc.

1. They directly kill the bacteria and cure disease.

2. They do not interfere in DNA or RNA replication.

3.For example; penicillin, sterptomycin, etc.

Types of Antibiotics

There are over 100 antibiotics but the majority indicate from only few types of drugs. Following are the main class of antibiotics:

  • Penicillin like penicillin and amoxicillin.
  • Cephalosprins like cephalrxin (keflex)
  • Macrolides like erythromycin(E-Mycin), clarithromycin(Biaxin) and azithromycin(Zithromax)
  • Fluoroqunolones like ciprofloxacin(Cipro),levofloxacin(Biaxin) and ofloxacin(Floxin)
  • Sulfonamides like co-trimoxazole(Bactrim) and trimeyhoprim(Proloprim)
  • Tetracyclines like tetracycline(Sumycin,Panmycin) and doxycycline(Vibremycin)
  • Aminoglycosides like gentamicin(Garamycin) and tobramycin(Tobrex)

Usually most of the antibiotics have two name, one trade or brand name which is given by the manufacturing drug company and another is generic name which is based on the antibiotic’s chemical structure. Example of trade name: Keflex, Zithromax ,etc. Example of generic name; cephalexin, azithromycin, etc.

Antibiotics resistance-a major problem

Uses of different antibiotics have a major problem of resistance to antibiotics. When the user uses the antibiotics once the same doze do not work on user. Since the resistant power of microorganism is increased to the antibiotics. The resistance may occur due to the mutation in the organisms or by transfer of resistance. When the organism get resistance to an antibiotic, the same disease take long time to be cured by the same antibiotic. Once the organism resist the antibiotic, the use of the same antibiotics give them a selective benefit over the organism which cannot resist antibiotics. As result resistant type organism get rapid multiplication.

Application of antibiotics

  1. Use as medicine: Antibiotics are use by many people in the world to control different diseases. They are also use for to treat different animal’s diseases.
  2. Useas food preservations: Antibiotics are use for purpose of preservation of especially like fresh meat, fish and poultry feeds .Due to the use of antibiotics foods can be kept for longer period of time, since it prevent food from bacteria.
  3. Use as supplement in animals feed: Antibiotics are use in the sector of animal husbandry. They are use as animal feed because they help to enhance the growth of the animals.


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Agrawal, sarita. principle of biology. 2nd edition . kathmandu: Asmita book Publication, 2068 ,2069.

Mehta, Krishna Ram. Principle of biology. 2nd edition. kathmandu: Asmita, 2068,2069.

Jorden, S.L. principle of biology. 2nd edition . Kathmandu: Asmita book Publication, 2068.2069.

1.Antibiotics are the chemical substance produce by mircooranism whcich are capable of conrolling the growth and development of microorganism.

2.Penicillin was the world's first antibiotics discovered by Alexander Flemming.

3.On the basis of action they are divided into two group.They are;Bacteriostatic agent and Bacteriocidal agent.

4.A major problems of use of antibiotics is that organism become resistant and may cause more disease.



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