Skip main navigation

What are antimicrobials

A brief overview of the three types of antimicrobial resistance and how they work.
pile of white books against white background

An antimicrobial is a drug that inhibits the growth or directly kills microbes. The first antimicrobial, Salvarsan, was discovered in 1910 and was an arsenic-containing drug effective for syphilis (Treponema pallidum). Penicillin was discovered in 1928 when Sir Alexander Fleming noticed that a contaminating mould prevent S. aureus growth.


Antimicrobial agents can be classified as resistant (non-susceptible), sensitive (susceptible) and intermediate.

Susceptible (sensitive): a microorganism is inhibited at a concentration that is achievable in the human body at standard dosing. Non-susceptible (resistant): a microorganism is not inhibited at a concentration that is clinically achievable in the human body at standard dosing. Intermediate: a microorganism is not reliably inhibited at a concentration that is clinically achievable in the human body at standard dosing.


Antibiotics act on bacteria. They may be administered in several ways:

  • Oral Therapy
  • Parenteral Therapy
    • Intravenous (IV)
    • Intramuscular (IM)
    • Inhaled
    • Miscellaneous (eg. Intrathecal, Intraperitoneal, Bladder Infusion, Pre-Rectal)

There are advantages and disadvantages to each method of delivery. Some antibiotics are available only as oral formulations or for parenteral delivery. The target tissue and type of infection can influence which method of delivery is used. [table “” not found /]


These are agents that act against fungal infections. Unlike bacteria, fungi are eukaryotes and significantly more difficult to target selectively because of their similarities to mammalian cells. Fungi have a cell wall, which is the target of action for antifungals.


This article is from the free online

Introduction to Practical Microbiology

Created by
FutureLearn - Learning For Life

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education