Ch 10 - Antimicrobial Drugs: History, Sources & Types

Controlling Microbial Growth in the Body: Antimicrobial Drugs

Introduction

Antimicrobial drugs are essential tools in modern medicine for controlling microbial growth and treating infectious diseases. This section explores the history, sources, and types of antimicrobial agents, providing foundational knowledge for microbiology students.

History of Antimicrobial Agents

Definitions and Early Discoveries

• Drugs: Chemicals that affect physiology in any manner.

• Chemotherapeutic agents: Drugs that act against diseases, including infections and cancer.

• Antimicrobial agents (antimicrobials): Drugs that specifically treat infections caused by microorganisms.

Pioneers in Antimicrobial Discovery

• Paul Ehrlich: Developed the concept of "magic bullets"—arsenic compounds that selectively killed microbes without harming the host.

• Alexander Fleming: Discovered Penicillium mold releases penicillin, the first true antibiotic effective against bacteria.

• Gerhard Domagk: Discovered sulfanilamide, the first widely used synthetic antimicrobial drug.

• Selman Waksman: Coined the term "antibiotics" for antimicrobial agents produced naturally by organisms, especially soil bacteria and fungi.

Types of Antimicrobial Agents

• Antibiotics: Antimicrobial agents produced naturally by microorganisms (e.g., bacteria, fungi).

• Synthetics: Antimicrobials that are completely synthesized in a laboratory.

• Semisynthetics: Chemically altered antibiotics that are more effective, longer lasting, or easier to administer than naturally occurring ones.

Additional info: Semisynthetic antibiotics are often designed to overcome limitations of natural antibiotics, such as poor absorption or rapid degradation.

Sources of Common Antibiotics and Semisynthetics

Microbial Origins of Antimicrobial Agents

Many antibiotics and semisynthetic drugs are derived from specific microorganisms. The following tables summarize key sources and their associated antimicrobials.

Microorganism	Antimicrobial
Penicillium chrysogenum	Penicillin G
Penicillium griseofulvum	Griseofulvin
Acremonium spp.	Cephalothin
Amycolatopsis orientalis	Vancomycin
Amycolatopsis rifamycinica	Rifampin
Bacillus licheniformis	Bacitracin
Bacillus polymyxa	Polymyxin
Micromonospora purpurea	Gentamicin
Pseudomonas fluorescens	Mupirocin
Saccharopolyspora erythraea	Erythromycin
Streptomyces griseus	Streptomycin

Microorganism	Antimicrobial
Streptomyces fradiae	Neomycin
Streptomyces aureofaciens	Tetracycline
Streptomyces venezuelae	Chloramphenicol
Streptomyces nodosus	Amphotericin B
Streptomyces avermitilis	Ivermectin
Streptomyces noursei	Nystatin

Additional info: The genus Acromonium was formerly called Cephalosporium. Streptomyces species are prolific producers of antibiotics, with many drugs named after their source organism.

Example: Penicillium chrysogenum and Penicillin

• Penicillium chrysogenum produces Penicillin G, which inhibits the growth of many Gram-positive bacteria.

• Zone of inhibition: In laboratory tests, the area around the mold where bacterial growth is prevented demonstrates the antibiotic effect.

Summary Table: Types of Antimicrobial Agents

Type	Description	Example
Antibiotic	Produced naturally by microorganisms	Penicillin from Penicillium
Semisynthetic	Chemically modified natural antibiotics	Amoxicillin
Synthetic	Completely synthesized in the laboratory	Sulfanilamide

Key Terms

• Antimicrobial agent: Any substance that kills or inhibits the growth of microorganisms.

• Antibiotic: A type of antimicrobial agent produced by living organisms, typically bacteria or fungi.

• Synthetic drug: An antimicrobial agent manufactured entirely by chemical processes.

• Semisynthetic drug: An antibiotic that has been chemically modified to improve its properties.

Applications and Importance

• Antimicrobial drugs are used to treat bacterial, fungal, and some protozoal infections.

• Understanding the source and type of antimicrobial agents helps in selecting appropriate therapy and combating resistance.