The word antimicrobial was derived from the Greek words anti, mikros and bios 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 and biotikos. 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 or semisynthetic or those which come from plants or animals. An antimicrobial is an agent that kills microorganisms or inhibits their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria and antifungals are used against fungi. They can also be classified according to their function. Agents that kill microbes are called microbicidal, while those that merely inhibit their growth are called biostatic.


Antimicrobials are classified in several ways, including:

1. spectrum of activity

2. effect on bacteria

3. mode of action

Antimicrobial (Drug) Resistance

Microbes are constantly evolving enabling them to efficiently adapt to new environments. Antimicrobial resistance is the ability of microbes to grow in the presence of a chemical (drug) that would normally kill them or limit their growth.