Fanny Hesse, the Woman Who Introduced Agar to Microbiology

Cultivating microorganisms in the lab has not always been what it is now. Thanks to Angelina Fanny Hesse (1850-1934), microbiologists now have a solid medium to grow microbes in the lab.

Before Hesse stepped onto the scene, bacteriologists were cultivating microorganisms on an assortment of food – potato, coagulated egg whites, and meat. In 1819, an epidemic of “bloody bread” broke out in Padua, Italy. The Venetian pharmacist Bartolomeo Bizio isolated the culprit on polenta and called it Serratia marcescens. Then in 1872, Joseph Schroeter published a paper demonstrating the separation of bacteria of different colors on cooked potatoes. Like Bizio’s experiments, Schroeter was able to transfer the microorganisms to fresh media over and over.

When Robert Koch came to the scene, he wanted to improve bacterial cultivation by introducing something that was solid, transparent, and sterile. He turned to gelatin which mycologists had been using for 30 years at the time. But gelatin had its own set of problems. At the standard bacterial growth temperature, 37 ˚C, gelatin liquefies. Some bacteria can also use gelatin as a nutrient source turning the once-solid medium into a gloppy mess. This made the use of gelatin-based media limited to cooler weather and would be useful to cultivate only a subset of microorganisms.

Hesse’s husband, Walther, was studying microbial contamination of air in Robert Koch’s lab during 1881 and 1882. In the summertime however, even the plates left out on the bench started to melt.

Hesse, who also made bacterial growth medium at home and worked unpaid as an illustrator for her husband’s publications, had an idea. She learned about agar-agar as a child from a neighbor who had emigrated from Java. In warmer climates, it was used as a gelling agent and Hesse often made jellies and puddings in warm weather without a problem.

When Hesse told her husband, he immediately reported this idea to Koch. Agar turned out to be well suited for repurposing for microbiology labs. It is thermal stable, resistant to microbial enzymes, and could be sterilized and stored for a long time. Koch eventually used it to cultivate Mycobacterium tuberculosis and published this finding in a paper in 1882. Only one sentence was included to describe the use of agar instead of gelatin without providing rationale for the switch. Hesse never received credit or financial benefit for her contribution.

Angelina Hesse was an overlooked heroine of modern microbiology. Many microbiologists use agar medium nearly every single day, but few know about Hesse’s contribution to modern bacterial cultivation. While credit is often given to the heads of the lab, let’s also celebrate the contributions of the lab members that are often at the center of discovery.

Further reading:

Walther and Angelina Hesse-Early Contributors to Bacteriology, ASM News, 1992.

The Introduction of Agar-agar into Bacteriology, Journal of Bacteriology, 1939.