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Antimicrobial Agent and Chemotherapy

Definition of Antimicrobial Agent

Antimicrobial agent refers to those chemical or physical agents which are used to kill microorganisms or prevent their growth.

There are present several types of microorganism which are responsible for infection or disease in animal or human body such as fungi, bacteria, virus, etc. Similarly, there are present different types of antimicrobial agents for each type of microorganisms such as antibacterial drugs, antifungal drugs, and antiviral drugs, etc.

Example of Antimicrobial Agent: Antibiotics, antiseptics, etc.

Characteristics of an Ideal Antimicrobial Agent

Ideal antimicrobial agent should contain these following properties;

  1. The first and most important requirement of an antimicrobial agent is it should contain the capability to kill or inhibit the growth of microorganisms.
  2. The antimicrobial agent should contain a broad-spectrum antimicrobial activity at low concentrations.
  3. It will kill or inhibit the pathogen without damaging the host.
  4. It will cause no allergic reaction in the host.
  5. Kill the pathogen before they mutate or resistant to it.
  6. An antimicrobial agent should be soluble in water or other solvents, for effective use.
  7. An antimicrobial agent must be stable, it means even if there is a change in the physical properties (pH, temperature, etc), the antimicrobial agent will not lose its germicidal action.
  8. An antimicrobial agent should be lethal to microorganisms and it should be non-toxic to humans or animals.
  9. Stay In target tissues for a long time to be effective.
  10. The antimicrobial agent should be available in large quantities and in an affordable price.
  11. The antimicrobial agent should possess deodorizing property because this property is a desirable attribute. Ideally, the disinfectant itself should either be odorless or possess a pleasant smell.
  12. While using an antimicrobial agent, it should not be necessary to raise the temperature beyond that normally found in the environment where it is to be used. 
  13. Until the antimicrobial agent can penetrate through surfaces, its germicidal action is limited solely to the site of application.

Antimicrobial Agent and Chemotherapy

  • When an antimicrobial agent used to treat any infectious disease is known as antimicrobial chemotherapy.
  • The term Chemotherapy first coined by Paul Ehrlich, who was a German medical researcher. He used the term to describe those chemical agents That kill pathogens without injuring the host.

Example of Antimicrobial Chemotherapy: Use of Antibacterial agents for bacterial infections.

Types of Antimicrobial Agent

There are present five types of antimicrobial agent such as;

  1. Antibacterial Agent.
  2. Antifungal Agent.
  3. Anthelminthic Agent.
  4. Antiprotozoal Agent.
  5. Antiviral Agent.

Antibacterial Drug or Antibiotic

  • The antibacterial drug or antibiotic is a type of antimicrobial agent which is used for the treatment of bacterial infection. 
  • Antibiotic or antibacterial agents also used for the treatment of protozoal infection, for example, Metronidazole antibiotic is effective against many parasitic infections.

Example of Antibacterial Drugs: Chloramphenicol, Clindamycin, Ethambutol, Lincosamides, Macrolides, Nitrofurantoin,Novobiocin, etc.

Classification of Antibacterial Drugs or Antibiotics

Antibacterial drugs are classified on different basis such as:

  1. Classification of Antibacterial Drugs based on the source.
  2. Classification of Antibacterial Drugs based on the type of action.
  3. Classification of Antibacterial Drugs based on the spectrum of activity.
A. Classification based on source of antibacterial agents

Antibiotics are divided into three classes based on the source of antibacterial agents such as; Semisynthetic antibiotic, Synthetic Antibiotic, and Natural Antibiotic.

  1. Semi-synthetic antibiotic

Semi-synthetic antibiotics are a type of antibiotic which is produced by a microbe that are subsequently modified by an organic chemist to increase their antimicrobial properties or to render them unique for a pharmaceutical patent.

Example of Semi-synthetic antibiotics : Ampicillin and amikacin

  1. Synthetic Antibiotic:

Synthetic antibiotics include those antibiotics which are man made in the laboratory.  The first synthetic antibiotic was organoarsenic compound salvarsan, now called arsphenamine, which is discovered by Paul Ehrlich.

Example of Synthetic antibiotics : sulphonamides, cotrimoxazole, quinolones,etc

  1. Natural Antibiotic:

Natural Antibiotics are not made of Synthetic material, they are produced naturally.

Example of Natural Antibiotics: Garlic, Honey, Cabbage, Grapefruit seed extract, Raw apple cider vinegar, Extra virgin coconut oil

B. Classification based on type of action

Antibiotics are divided into two classes based on the type of action of antibacterial agents such as; bacteriostatic and bactericidal.

  1. Bacteriostatic: 

Those antibiotics, which  kill the targeted bacteria by inhibiting their growth are known as Bacteriostatic.

Examples of Bacteriostatic: Chloramphenicol, Clindamycin, Ethambutol, Lincosamides, Macrolides, Nitrofurantoin, Novobiocin, etc.

  1. Bactericidal:

Those antibiotics, which inhibit the targeted bacteria by destroying their cell wall are known as bactericidal.

Example of Bactericidal:  penicillin, daptomycin, fluoroquinolones, metronidazole, nitrofurantoin, co-trimoxazole, telithromycin, etc.

C. Classification based on spectrum of activity

Antibiotics are divided into two classes based on the spectrum of activity such as; broad-spectrum antibiotics and narrow-spectrum antibiotics.

  1. Broad-spectrum antibiotics: Broad-spectrum antibiotics act against a wide range of bacterial infections. (Broad-Spectrum antibiotics act against both gram-positive and Gram-Negative bacteria)

Example of Broad-spectrum antibiotics: Ampicillin, Tetracyclines, Amoxicillin/clavulanic acid, etc.


  • Active against a wide range of bacteria.
  • No Need to identify the infectious pathogen with real certain before Beginning treatment.


  • When newborn infants start to receive broad-spectrum antibiotics during their first year of life they are at high risk of developing childhood asthma.
  • Broad-spectrum antibiotics can increase the risk of drug resistance.
  • Sometimes broad-spectrum antibiotics also affect the beneficial microbiota of the human body.
  1. Narrow spectrum antibiotics: Narrow spectrum antibiotics act against a specific bacterial infection.

Example of Narrow spectrum antibiotics: macrolides and vancomycin.


  1. Narrow spectrum antibiotics only act against targeted bacteria and don’t affect the beneficial microbiota of the human body.
  2. Narrow-spectrum antibiotic  are highly specific
  3. Narrow-Spectrum antibiotics will cause Less resistance of the bacteria because it only acts on the specific bacteria.


  1. Spectrum antibiotics can be used if the pathogen is identified, If you don’t choose the correct antibiotic for a specific bacteria, it will not work.

Antifungal Drug

  • Antifungal drugs or agents are a type of antifungal agent which is used to kill or prevent the growth of fungi.
  • Antifungal drugs are a pharmaceutical fungicide or fungistatic, which is also known as an antimycotic medication.
  • Antifungal drugs are used for the treatment or prevention of mycosis such as an athlete’s foot, ringworm, candidiasis (thrush), serious systemic infections such as cryptococcal meningitis, and others.

Types of Antifungal Agent

Antifungal agents are divided into two groups such as Local Antifungal agents and Systemic Antifungal agents. 

  1. Local Antifungal agents: This type of drug is usually administered topically or vaginally, based on the condition being treated. 
  2. Systemic Antifungal agents: This type of drug is usually administered orally or intravenously.

Example of Antifungal Drugs: Butoconazole, Clotrimazole, Econazole, Fenticonazole, Isoconazole, Ketoconazole.

Antiviral Drug

  • Antiviral drugs or antiviral agents used for the treatment of viral infection.
  • Like antibiotics, Antiviral drugs do not destroy or Kill the targeted virus instead it inhibits the development or growth of the targeted virus.
  • Like antibacterial drugs, Antiviral drugs also act against a specific virus.
  • The most publicized antiviral agent is Tamiflu which is used for the treatment of Influenza type A (inhibits the viral molecule neuraminidase).

Example of Antiviral Drug: Abacavir Use for HIV, Acyclovir (Aciclovir) Use for herpes, Adefovir Use for chronic Hepatitis B, Amantadine Use for influenza, Ampligen, etc.

Antiprotozoal Drug

  • Antiprotozoal agents are a type of antimicrobial agent which is used in treatment of protozoan infection.
  • Antiprotozoals are used for treatment of amebiasis, giardiasis, cryptosporidiosis, microsporidiosis, malaria, babesiosis, trypanosomiasis, Chagas disease, leishmaniasis, and toxoplasmosis.

Example of Antiprotozoal Drugs: Eflornithine, Furazolidone, Hydroxychloroquine, Melarsoprol, Metronidazole.

Anthelmintic Drug

  • Anthelmintics or antihelminthics are a type of antiparasitic drugs, which is used to destroy or kill the parasitic worms (helminths) and other internal parasites without causing significant damage to the host. 
  • Anthelmintics also known as vermifuges or vermicides. 

Example of Anthelmintics Drugs: Albendazole, Mebendazole, Thiabendazole, Fenbendazole, etc.

Mode of Action or Mechanism of Antimicrobial Drugs

Mode of Action of Antimicrobial Agents
Mode of Action of Antimicrobial Agents

Generally, Antimicrobial drugs or Antimicrobial Agents act on microbial structure or function which usually differs from animals or the host body (Human). This difference is exploited in exerting a bactericidal, or killing, effect, or a bacteriostatic, or growth-inhibiting, the effect on bacteria while having minimal effects on host cells.

There are present 5 mode of action of antimicrobial Agent such as;

  1. Inhibition of cell wall synthesis.
  2. Disruption of cell membrane function.
  3. Inhibition of protein synthesis.
  4. Inhibition of nucleic acid synthesis.
  5. Action as antimetabolites

Inhibition of cell wall synthesis

  • Most Importantly many bacterial and fungal cells contain rigid external cell walls, whereas animal cells lack cell walls. This difference of cell wall between microbes and animals, allows the antimicrobial agents to destroy the microorganism without harming the host or animal.
  • Antibiotics such as penicillin and cephalosporin have a chemical structure called a β-lactam ring, which binds with the enzymes that help in the cross-linking of peptidoglycans in the bacterial cell wall. By interfering with the cross-linking of tetrapeptides, these antibiotics prevent cell wall synthesis.
  • Fungi and Archaea are unaffected by these antibiotics because they lack peptidoglycan on their cell walls, as are the L forms of bacteria that totally lack cell walls.

Disruption of Cell Membrane Function

  • The cell membrane of bacteria and fungi is sufficiently different from animal cells which allows the antimicrobial agents to destroy the microbes without harming the host body cell.
  • In gram-negative bacteria (outer membrane rich in phospholipids), a polypeptide antibiotic, known as polymyxins, which act as a detergent by binding with the phospholipids of the outer membrane and as a result, it distorts the bacterial cell membrane (polymyxins do not act on fungi)
  • In Fungi, Polyene antibiotics (amphotericin B) act by binding with particular sterols present in the membranes of fungal (and animal) cells. (polyenes do not act on bacteria.)

Inhibition of Protein Synthesis

  • Protein is a most important component Of a cell which is required for DNA, RNA, and ribosome. The key difference between the animal cell and bacterial cell is, The bacterial cell has a 70s ribosome whereas animal cell has an 80s ribosome Which allows the antimicrobial agents to destroy the microbes without harming the animal cells.
  • Aminoglycoside antibiotics, for example, streptomycin act on the 30S portion of bacterial ribosomes by interfering with the accurate reading (translation) of the mRNA message.
  • Whereas the Chloramphenicol and erythromycin act on the 50S portion of bacterial ribosomes, inhibiting the formation of the growing polypeptide. (Remember they don’t affect the animal cell because animal cell ribosomes consist of 60S and 40S )

Inhibition of Nucleic Acid Synthesis

  • The key difference in enzymes that are used by bacterial and animal cells to synthesize nucleic acids allows the selective action of antimicrobial agents.
  • Antibiotics of the rifamycin family, inhibit the synthesis of RNA by binding with the bacterial RNA polymerase.

Action as Antimetabolites

  • Antimetabolites are a type of substances that inhibit the utilization of metabolites in microbial cells and therefore prevent a cell from carrying out necessary metabolic reactions.
  • Antimetabolites function in two ways:
  1. Competitively inhibiting enzymes: In this process, the inhibition of enzymatic reaction is occurred by the binding of a substrate to the enzyme’s active site but cannot react, as a result, the enzyme is unable to function, and metabolism will slow or even cease if enough enzyme molecules are inhibited.
  2. By being erroneously incorporated into nucleic acids: Antimetabolites such as the purine analog vidarabine and the pyrimidine analog idoxuridine are erroneously incorporated into nucleic acids. When incorporated into a nucleic acid, they garble the information that it encodes because they cannot form the correct base pairs during replication and transcription.

Important Note: Purine and pyrimidine analogs are generally as toxic to animal cells as to microbes because alleles use the same purines and pyrimidines to make nucleotides. These agents are most useful in treating viral infections because viruses incorporate analogs more rapidly than do cells and are more severely damaged.

Side Effects of Antimicrobial Agents

Several side effects of antimicrobial agents such as ;

  1. Allergy:  Breakdown products of penicillins combine with proteins in body fluids to form a molecule that the body treats as a foreign substance and started allergic reactions
  1. Toxicity: Sometimes, few antimicrobials do exert toxic effects on the patients receiving them.
  1. Inhibition of Normal Microflora
  • Broad-spectrum antibiotics inhibit both the pathogens and normal flora of the animal body. When these microflora is disturbed, other organisms, such as Candida yeast, invade the unoccupied areas and start to increase their number rapidly which results in superinfection. Superinfections are difficult to treat because they are susceptible to a few antibiotics.
  • If someone uses penicillin or aminoglycosides for a long time it can abolish natural microflora.

Regenerative medicine

When renewing and repairing of the body is done through the various treatments is known as Regenerative medicine, it is a field of medicine. There is a various treatment process which is considered as Regenerative medicine, which includes facilitate repair, rejuvenation, and offer extensive anti-aging properties to treat conditions like fatigue, aging, and joint pain.

Frequently Asked Questions with Answer

  1. What is Antimicrobial Agent?
  2. What Is Antimicrobial Chemotherapy?
  3. What are the disadvantages of Antimicrobial Agents?
  4. What are the examples of antimicrobial agents?
  5. What are the five main classes of antimicrobial drugs?
  6. How do antimicrobial agents kill bacteria?
  7. What are chemical antimicrobial agents?


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What is Karyotyping? What are the scope of Microbiology? What is DNA Library? What is Simple Staining? What is Negative Staining? What is Western Blot? What are Transgenic Plants? Breakthrough Discovery: Crystal Cells in Fruit Flies Key to Oxygen Transport What is Northern Blotting? What is Southern Blotting?
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