In 1939 the search was on for chemicals that could treat bacterial infections – a really serious issue with war looming. In Oxford Howard Florey and Ernst Chain came across Fleming’s work and started to look at penicillin. They infected mice with pneumonia and injected half of them with penicillin. The next day all the injected mice were fine, and all the others were dead. Chain rightly described it as ‘a miracle’ and work began to grow large quantities of mould so that enough penicillin would be available to treat soldiers with infected wounds as well as everyone else who would benefit. It took a long time to find a way to do this, however.

It was 1941 before enough penicillin was produced to treat the first patient. He began to recover, but the penicillin ran out before he was cured and, sadly, he died. In 1942, the amount produced was only enough to treat about 100 people. But by 1943 there was enough penicillin to treat every Allied soldier who needed it. Penicillin helped the Allies win World War 2 – not bad for a tiny mould!