The antibiotic era began with Alexander Fleming’s discovery of penicillin at St Mary’s Hospital in London in 1928. Fleming had witnessed first-hand the terrible effects of infectious disease while serving in the Royal Army Medical Corps in World War I, watching helplessly as wounded men died of sepsis – a reaction of the immune system to infection, damaging tissues and organs – and he became interested in developing a better treatment to replace the often ineffective antiseptics used at the time.
Fleming had been growing colonies of staphylococcus – a type of bacterium that is ubiquitous on human skin and can easily infect wounds – in Petri dishes, when he noticed an unexpected development. On one dish, which had been left open by mistake while Fleming was on holiday, there was a spot of green mould that was inhibiting the growth of the bacteria. Following some experimentation Fleming discovered that an extract from the mould, Penicillium notatum, was able to kill a wide variety of bacteria.