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What are antimicrobials

A brief overview of the three types of antimicrobial resistance and how they work.
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© Unsplash image by Beatriz Perez Moya
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.


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Introduction to Practical Microbiology

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