The discovery of penicillin
In 1928, while experimenting on staphylococcal bacteria, Alexander Fleming noticed that one of his cultures was contaminated by a mould which appeared to kill the bacteria growing around it. Further tests showed that the mould – penicillin – was antibiotic. In follow-up studies, a broth extracted from the mould, was non-toxic when given to rabbits and mice.
The broth rapidly disappeared from the animal’s blood but appeared to kill bacteria slowly in the test tube, leading Fleming to believe that penicillin was potentially useful as an antiseptic for surface infections. A few patients with eye infections were successfully treated using impure extracts of penicillin broth in the 1930s but little more came from the discovery.
In 1940 the search for antibiotics to reduce death from septic infection led Howard Florey and Ernst Chain to investigate Fleming’s penicillin broth using a mouse protection test. In the test, Florey and Chain injected eight mice with a lethal suspension of bacteria and four of these were also given penicillin. The four mice which received penicillin lived, while all the rest died. This proof that penicillin worked as an antibiotic against serious bacterial infections eventually led to the purification and mass production of penicillin.