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Who Invented The Petri Dish?

2021-11-25

Who Invented The Petri Dish?

Friday would have been the 167th birthday of Julius Richard Pizzeri, the inventor of the famous Petri dish.

In 1876, bacteriologist Robert Koch discovered the bacterium that causes anthrax; This is the first time anyone has ever traced a disease to the microbe that caused it. It was a great discovery that shaped the curriculum of microbiology and medicine; One hundred and fifty years later, it's easy to forget the unremarkable details, like the many bacteria Koch cultivated on potato chips in the early days. It doesn't get any better than that. Today, he is credited with inventing better (and less starchy) ways to grow bacteria, especially small round dishes known as Petri dishes. But as the name suggests, the Petri dish was not Koch's invention at all -- though Koch does deserve credit for knowing a good idea when he sees it.

Petry joined Koch's laboratory at the Imperial German Sanitary Office in 1877, and soon after he invented a decent substitute for the potato: a round, shallow glass dish with a lid. It quickly caught on at Koch's lab, where researchers grew bacteria on various mixtures of gelatin and beef soup. Design has not changed much since the late 1870s; Modern plates also come in plastic versions, most now have rings on the LIDS to make them easier to fold, but the basic shape is the same.

But in the field of early bacteriology, all was not well, as Koch and his assistants were arguing over how to feed their bacterial colonies, which they had put into petri dishes. The beef soup provided most of the nutrients the colony needed to grow, but it turned out to be nearly impossible to pick out the bacteria from the resulting soup. They need something more solid to grow on.

Gelatin -- a protein found in collagen and used to make familiar wobbly snacks like jellies -- seems like a good way to hold things in place. But many species of bacteria just eat gelatin. In other cases, it melts into a gunk at the heat of an incubator. Good luck isolating the bacteria from it.

Ever since her husband, Walter Hesse, joined Koch's lab in 1881, Angelina Hesse has been cooking beef soup for countless bacteria. She suggests using AGAR -- a compound found in the cell walls of red algae and often used to make jellies, ice cream or soups -- to strengthen the bacteria's growth medium. She learned this technique from Dutch friends who had learned it from their neighbors during sojourns in Indonesia; Angelina Hesse was the first to bring AGAR into the biology lab (although today her husband and his boss still get major credit, which gives her something else in common with Petri).

Mixing AGAR with a nutrient-rich broth in a petri dish proved to be an excellent way to grow and study bacteria, which is how Koch finally identified the bacterium that causes TB.

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