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Antimicrobials: An Introduction

Antibiotics Versus Antimicrobials

An ANTIBIOTIC is a low molecular substance produced by a microorganism that at a low concentration inhibits or kills other microorganisms.

An ANTIMICROBIAL is any substance of natural, semisynthetic or synthetic origin that kills or inhibits the growth of microorganisms but causes little or no damage to the host.

All antibiotics are antimicrobials, but not all antimicrobials are antibiotics.

The word antimicrobial was derived from the Greek words anti (against), mikros (little) and bios (life) and refers to all agents that act against microbial organisms.  This is not synonymous with antibiotics, a similar term derived from the Greek word anti (against) and biotikos (concerning life).  By strict definition, the word “antibiotic” refers to substances produced by microorganisms that act against another microorganism.  Thus, antibiotics do not include antimicrobial substances that are synthetic (sulfonamides and quinolones), or semisynthetic (methicillin and amoxicillin), or those which come from plants (quercetin and alkaloids) or animals (lysozyme).

In contrast, the term “antimicrobials” include all agents that act against all types of microorganisms – bacteria (antibacterial), viruses (antiviral), fungi (antifungal) and protozoa (antiprotozoal). 

Notice that the term “antibacterials”, being the largest and most widely known and studied class of antimicrobials, is often used interchangeably with the term “antimicrobials” and will be the major focus of this website.

Antimicrobials are classified in several ways, including:

  1. spectrum of activity
  2. effect on bacteria
  3. mode of action



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