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•  Florey and Chain’s experiments to test penicillin on bacterial infections in mice

The first chemical compound found to have antibiotic properties was penicillin, which was identified by Alexander Fleming in 1928

  • The discovery of penicillin was a fortuitous accident, resulting from the unintended contamination of a dish containing S. aureus
  • A Penicillium mould began to grow on the plate and a halo of inhibited bacterial growth was observed around the mould
  • Fleming concluded that the mould was releasing a substance (penicillin) that was killing the nearby bacteria 

The Discovery of Penicillin


Medical Applications

The medical applications of penicillin as an antibiotic were demonstrated by an Australian scientist, Sir Howard Florey, in 1940

  • Working with another scientist (Ernst Chain) and a team of researchers, Florey tested penicillin on infected mice
  • Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
  • The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential

Florey and Chain Experiment

florey experiment

Historical Significance

In 1945, Howard Florey, Ernst Chain and Alexander Fleming were collectively awarded the Nobel Prize for Medicine 

  • Following the chemical determination of penicillin structure in 1945, several synthetic derivatives have since been created
  • These derivatives (including methicillin) offer many benefits including a broader spectrum, more stability and greater tolerance

Nobel Laureates (Medicine – 1945)

fleming florey chase