Antibiotics — Core Principles

Core Principles

Antibiotics are chemical substances, primarily derived from microorganisms, that can kill or inhibit the growth of bacteria. Their discovery, notably penicillin by Alexander Fleming, revolutionized medicine.

The core principle of antibiotic action is 'selective toxicity,' meaning they target bacterial structures or processes (like cell wall synthesis, protein synthesis on 70S ribosomes, nucleic acid synthesis, or specific metabolic pathways) that are absent or significantly different in human cells, thus minimizing harm to the host.

Antibiotics are classified based on their spectrum of activity (narrow-spectrum vs. broad-spectrum) and their effect on bacteria (bactericidal, which kill, or bacteriostatic, which inhibit growth). While incredibly effective against bacterial infections, antibiotics are ineffective against viruses.

A major global health challenge is antibiotic resistance, where bacteria evolve to withstand antibiotic effects, often driven by the misuse and overuse of these drugs. Responsible antibiotic stewardship, including completing full prescribed courses, is crucial to preserve their efficacy.

Important Differences

vs Antiseptics and Disinfectants

Aspect	This Topic	Antiseptics and Disinfectants
Target Organism	Antibiotics (e.g., Penicillin)	Antiseptics (e.g., Dettol), Disinfectants (e.g., Bleach)
Application	Internal use (inside living tissues/body)	External use (on living tissues for antiseptics; on inanimate objects for disinfectants)
Selective Toxicity	High (target specific bacterial pathways, minimal host harm)	Low (broad-spectrum toxicity, generally harmful to host cells at effective concentrations)
Mechanism	Specific biochemical targets (e.g., cell wall synthesis, protein synthesis)	General cellular damage (e.g., protein denaturation, membrane disruption)
Concentration	Effective at low concentrations	Require higher concentrations for efficacy
Resistance	Bacteria can develop specific resistance mechanisms	Less common for bacteria to develop specific resistance; tolerance can occur

Antibiotics are highly specific antimicrobial agents designed for internal use in living organisms, exhibiting selective toxicity by targeting unique bacterial structures or metabolic pathways. They are effective at low concentrations and bacteria can develop specific resistance mechanisms against them. In contrast, antiseptics are applied externally to living tissues, and disinfectants to inanimate objects. Both antiseptics and disinfectants have low selective toxicity, causing general cellular damage to a wide range of microbes and host cells at higher concentrations. While tolerance can occur, specific resistance mechanisms against antiseptics/disinfectants are less common compared to antibiotics.