Gross, old penicillin mold was just auctioned for more than $14,000. Here's why.

Mold is ... the new gold? Leave what's sitting in the back of your fridge long enough — for the better part of a century — and it could one day be worth a pretty penny: at least if we're talking Dr. Alexander Fleming's mold, which helped him discover the antibiotic penicillin in 1928 and for which he received a Nobel Prize in 1945.

A disc of that mold was auctioned to an unnamed buyer for $14,617 at Bonhams auction house on Wednesday, from a collection Fleming's niece owns.

The high price tag reflects the historical value of the discovery. Penicillin, a group of antibiotics, is one of the most influential, ubiquitous drugs of the 20th century, revolutionizing health care with bacteria-fighting, life-saving medicine.

Though the back of the mold disc is inscribed by Fleming as "the mold that first made penicillin," it might not be the exact mold, the Guardian reports. He made quite a few moldy gifts from the original culture for various luminaries. 

Fleming "sent these samples out to dignitaries and to people in the scientific world, almost as a kind of holy relic," said Matthew Haley, Bonham's director of books and manuscripts, according to the Associated Press.

Folklore says penicillin was discovered by accident, when Fleming returned to his lab at St. Mary's Hospital in London after holidaying in Scotland. His colleagues were prone to messiness — a huge blessing in disguise, it would later turn out — so some of his petri dishes were full of bacteria and mold. But the area surrounding the mold curiously appeared to be free from bacteria. And the rest was history. 

"When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionize all medicine by discovering the world's first antibiotic, or bacteria killer," Fleming wrote of that day, PBS reports. "But I guess that was exactly what I did."

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