Penicillin, Streptomycin — Definition

Definition

Antibiotics are a remarkable class of drugs that have fundamentally transformed modern medicine, allowing us to effectively combat bacterial infections that were once deadly. At their core, antibiotics are chemical substances designed to either kill bacteria (bactericidal) or inhibit their growth and reproduction (bacteriostatic), giving the host's immune system a chance to clear the infection.

What makes them so powerful is their 'selective toxicity' – they target specific structures or processes in bacterial cells that are either absent or significantly different in human cells, thereby minimizing harm to the patient.

This selectivity is crucial for their therapeutic utility.

Historically, the discovery of antibiotics began with serendipity. Penicillin, the first true antibiotic, was famously discovered by Alexander Fleming in 1928. He observed that a mold, *Penicillium notatum*, inhibited the growth of *Staphylococcus* bacteria on an agar plate.

This accidental observation paved the way for its isolation and mass production by Howard Florey and Ernst Chain, marking the dawn of the antibiotic era. Penicillin belongs to the beta-lactam class of antibiotics, characterized by a distinctive four-membered beta-lactam ring in its chemical structure.

Its primary mechanism of action involves interfering with the synthesis of the bacterial cell wall, a vital protective layer unique to bacteria. By inhibiting the enzymes responsible for cross-linking peptidoglycan strands, penicillin weakens the cell wall, leading to bacterial lysis and death.

It is primarily effective against Gram-positive bacteria and some Gram-negative cocci, making it a narrow-spectrum antibiotic.

Following penicillin's success, the search for new antibiotics intensified. This led to the discovery of streptomycin in 1943 by Selman Waksman and his team from *Streptomyces griseus*. Streptomycin represents a different class of antibiotics known as aminoglycosides.

Unlike penicillin, which targets the cell wall, streptomycin acts by inhibiting bacterial protein synthesis. It achieves this by binding irreversibly to the 30S ribosomal subunit of bacteria, causing misreading of mRNA and premature termination of protein synthesis.

This disruption leads to the production of non-functional proteins, ultimately killing the bacterial cell. Streptomycin is a broad-spectrum antibiotic, effective against a wide range of Gram-negative bacteria and, importantly, against *Mycobacterium tuberculosis*, the causative agent of tuberculosis.

Its discovery was a monumental step in treating this devastating disease. However, like all antibiotics, both penicillin and streptomycin have faced challenges, particularly the emergence of bacterial resistance, which continues to drive the need for ongoing research and responsible use.