Class 12 Chemistry Chemistry In Everyday Life Antimicrobials


  • Diseases in human beings and animals may be caused by a variety of microorganisms such as bacteria, virus, fungi and other pathogens.
  • An antimicrobial tends to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (antifungal agents), virus (antiviral agents), or other parasites (antiparasitic drugs) selectively.
  • Antibiotics, antiseptics and disinfectants are antimicrobial drugs.


  • Antibiotics are used as drugs to treat infections because of their low toxicity for humans and animals.
  • An antibiotic is a substance produced wholly or partly by chemical synthesis, which in low concentrations inhibits the growth or destroys microorganisms by intervening in their metabolic processes.
  • In order to find chemicals this will affect the invading bacteria and not the host.
  • Paul Ehrlich, a German bacteriologist, conceived this idea. He investigated arsenic based structures in order to produce less toxic substances for the treatment of syphilis.
  • He developed the medicine, arsphenamine, known as salvarsan.
  • Although salvarsan is toxic to human beings, its effect on the bacteria, spirochete, which causes syphilis, is much greater than on human beings.
  • He noted that there is similarity in structures of salvarsan and azodyes. The –As = As– linkage present in arsphenamine resembles the –N = N – linkage present in azodyes in the sense that arsenic atom is present in place of nitrogen.
  • In 1932, he succeeded in preparing the first effective antibacterial agent, prontosil, which resembles in structure to the compound, salvarsan. Soon it was discovered that in the body prontosil is converted to a compound called sulphanilamide, which is the real active compound. Thus the sulpha drugs were discovered.
  • A large range of sulphonamide analogues was synthesised. One of the most effective is sulphapyridine.
  • Despite the success of sulphonamides, the real revolution in antibacterial therapy began with the discovery of Alexander Fleming in 1929, of the antibacterial properties of a Penicillium fungus.
  • Antibiotics have either cidal (killing) effect or a static (inhibitory) effect on microbes.
  • A few examples of the two types of antibiotics are as follows:

Bactericidal                      Bacteriostatic

Penicillin                           Erythromycin

Aminoglycosides             Tetracycline

Ofloxacin                           Chloramphenicol

  • Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are said to be broad spectrum antibiotics.
  • Those are effective mainly against Gram-positive or Gram-negative bacteria are narrow spectrum antibiotics.
  • If effective against a single organism or disease, they are referred to as limited spectrum antibiotics.
  • Penicillin G has a narrow spectrum. Ampicillin and Amoxicillin are synthetic modifications of penicillin’s. These have broad spectrum.
  • It is absolutely essential to test the patients for sensitivity (allergy) to penicillin before it is administered.
  • In India, penicillin is manufactured at the Hindustan Antibiotics in Pimpri and in private sector industry.



  • Chloramphenicol, isolated in 1947, is a broad spectrum antibiotic.
  • It is rapidly absorbed from the gastrointestinal tract and hence can be given orally in case of typhoid, dysentery, and acute fever, certain form of urinary infections, meningitis and pneumonia.
  • Vancomycin and ofloxacin are the other important broad spectrum antibiotics.
  • The antibiotic dysidazirine is supposed to be toxic towards certain strains of cancer cells.


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