Penicillin started as a chance observation. My only merit is that I did not neglect the observation,” said Alexander Flemming, a Scottish scientist who discovered the latter.

In 1928, Flemming was carrying out studies about Influenza and properties of infectious bacteria, but some sources say that he even had an initiative to develop a drug that cures all types of diseases. So, after preparing his solution, the 47-year old back then went for vacation in London.

Upon coming back, he realised that he had forgotten to place his solution into an incubator. Consequently, a group of mould spores had surfed through his lab and around his petri dish. Little did he know that the accidental leak was about to germinate a medical revolution.

Studying this mysterious phenomenon, the scientist discovered that the mould was secreting a chemical compound that killed bacteria. The mould was a species in the penicillium genus, so Flemming dubbed his antibacterial compound Penicillin. Naturally, the penicillium mould constantly produces penicillin to defend against its threats.

So, it destroys the bacteria by weakening its cell wall and causes them to die, allowing a person to recover from a bacterial infection, according to livescience.com.

For decades, after Flemming’s discovery, Penicillin remained a laboratory curiosity, but during World War II, researchers started isolating the compounds and grew the mould in larger quantities.

They went on winning Nobel Prize in Physiology and Medicine, that is when Penicillin started to be commercially available.

As of now, Penicillin remains one of the most important life-saving antibiotics used in medicine.