What is the name of the antibiotic produced by the fungus Penicillium?

The antibiotic produced by certain fungi in the genus Penicillium is penicillin. It was famously noticed by Alexander Fleming in 1928, when a Penicillium mold contaminated a bacterial culture and prevented bacteria from growing around it.

Fleming called the antibacterial substance penicillin, but turning the observation into a practical medicine required later work. During the late 1930s and early 1940s, Howard Florey, Ernst Chain, and their colleagues purified, concentrated, and tested it. Large-scale production during World War II made penicillin available for treating serious bacterial infections, especially infected wounds. Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine.

Penicillin belongs to the beta-lactam class of antibiotics. It interferes with bacterial cell-wall construction, making susceptible bacteria rupture as they grow. Not every Penicillium species produces penicillin, and the modern industrial source was historically associated with Penicillium notatum and later Penicillium chrysogenum. Erythromycin, tetracycline, and streptomycin come from different microbial sources.