Today an 89-year-old piece of mold sold for $14,751 at an auction house in London. As The New York Times reports, the sample is part of the original culture used by Alexander Fleming to grow penicillin.

In 1928, the Scottish scientist accidentally discovered the life-saving antibiotic as a result of his slovenly lifestyle. Fleming had a habit of leaving out bacteria-filled petri dishes to fester around his home for weeks. He was disinfecting old dishes one day when he noticed that a spot of fungus had appeared on one of them and had killed the surrounding bacteria. Apparently, the fungus was a rare strain of penicillium that had blown in from an open window and found its way on to the sample.

Part of that original batch was purchased today, March 1, from Lot 92 at Bonhams for a five-figure sum. The back of the sample is signed by Fleming himself with the message, “The mould that first made penicillin.” Other historic mold samples from Fleming’s lab have been gifted to Winston Churchill, Prince Philip, Marlene Dietrich, and Pope Pius XII.

[h/t The New York Times]