How Antibiotics Combat Bacterial Infections
Antibiotics are medications designed to kill or inhibit the growth of bacteria causing infections. They work by targeting specific bacterial structures or processes that differ from human cells, such as cell wall synthesis, protein production, or DNA replication. For example, beta-lactam antibiotics like penicillin disrupt the bacterial cell wall, leading to cell lysis and death, while others like tetracyclines block protein synthesis essential for bacterial survival.
Key Mechanisms of Antibiotic Action
Antibiotics are classified by their primary targets: bactericidal ones directly kill bacteria by interfering with vital functions, whereas bacteriostatic types slow growth to allow the immune system to clear the infection. Common mechanisms include inhibiting cell wall formation (e.g., vancomycin), disrupting metabolic pathways (e.g., sulfonamides), or damaging DNA (e.g., fluoroquinolones). This specificity minimizes harm to human cells, making antibiotics effective against infections like pneumonia or urinary tract infections.
A Practical Example: Penicillin in Action
Consider a streptococcal throat infection treated with penicillin. The antibiotic binds to penicillin-binding proteins in the bacterial cell wall, preventing cross-linking of peptidoglycan chains. This weakens the wall, causing the bacteria to burst under osmotic pressure. In practice, a patient might take oral penicillin for 10 days, reducing symptoms within 24-48 hours as bacterial numbers drop, illustrating how targeted action resolves the infection efficiently.
Why Antibiotic Resistance Develops and Its Implications
Resistance develops when bacteria evolve mechanisms to evade antibiotics, often through genetic mutations or acquiring resistance genes via plasmids. Overuse or misuse of antibiotics—such as incomplete courses or in agriculture—exposes bacteria to sub-lethal doses, favoring survival of resistant strains via natural selection. This leads to 'superbugs' like MRSA, making infections harder to treat and contributing to over 700,000 annual deaths globally, emphasizing the need for stewardship to preserve antibiotic efficacy.