What are antibiotics primarily derived from?

Antibiotics are primarily derived from natural products of bacteria and fungi. This stems from the discovery of penicillin by Alexander Fleming in 1928, which was the first true antibiotic and was obtained from the mold Penicillium notatum. Many antibiotics are produced by certain strains of bacteria, such as those in the genus Streptomyces, and various fungi, which synthesize these compounds as a defense mechanism against competing microorganisms.

The natural origin of antibiotics allows them to effectively target specific bacterial functions or structures because they evolved in the presence of these bacteria and are therefore often more effective and less toxic to human cells. While synthetic and semi-synthetic antibiotics have been developed to enhance efficacy and broaden the spectrum of activity, the foundational compounds were derived from natural sources. The reliance on natural products underscores the importance of biodiversity in the discovery and development of antimicrobial agents.