Google the word microbiology, and the first few images you will see are Petri dishes containing solid growth media, also known as agar plates. Microbiologists use these plates containing food to grow the microorganisms they study.

A key ingredient in solid growth media is called agar, the solidifying agent. This ingredient originated from a relatively unknown person—her name does not come to mind as quickly as Leeuwenhoek or Pasteur—though her contribution was arguably one of the most important to the field’s progress.

This article introduces you to Angelina Fanny Hesse, the woman who made this significant impact on microbiology. And you will learn about this crucial ingredient in microbiological growth media that scientists have used since the early 1880s.

What is Agar?

Agar is the solidifying agent in microbiological growth media, meaning agar makes it possible to grow microorganisms on a solid surface in a plate instead of in liquid broth. In liquid, you can grow a large amount of a clone or mixture of microbes in suspension, while on agar plates, you can grow individual clones or colonies that can be distinguished by appearance or analyzed separately for specific traits.

Before agar, solid microbiological growth media was done on potato slices, gelatin, polenta, meat, and coagulated egg whites. The closest ingredient to agar was gelatin. But gelatin presents problems for microbiologists: it melts at a temperature commonly used to grow microorganisms, 37ºC, and some bacteria can degrade it. In warm conditions, gelatin can melt, and the individual colonies drop back into suspension. And if the bacteria you isolate can degrade gelatin, you find liquid instead of solid media when you return to your agar plates.

So, without a suitable solid medium, microbiologists needed to find something better.

How Did We Come to Use Agar in Microbiology?

Angelina Fanny Hesse (Figure 1), called Lina by her family, was the one who knew about something better for making solid growth media. Hesse and her husband Walther were part of Robert Koch’s lab in Germany. While a student, Walther was struggling with growing microorganisms from air due to the inherent issues of working with gelatin in microbiology.

According to their grandson, Wolfgang Hesse, Walther noticed her jellies and puddings were not melting and asked what she used. So, Hesse told him about this ingredient called agar she added to maintain the consistency of her foods even in warm weather. She had used agar while cooking at home ever since a neighbor from Indonesia introduced her to it when she was a child in New York.

Walther then took this helpful information about agar that he learned from Hesse and shared it with Koch. The lab now had a substance similar to gelatin that lacked the issues of melting at 37ºC or being degraded by bacteria. Koch documented the use of agar in their growth media in his publications. However, Koch credited neither Lina nor Walther for this contribution, which is why Hesse remains relatively unknown even today.

Angelina Fanny Hesse’s introduction of agar to microbiology is arguably one of the most important tools for moving the field forward.

Photo of Angelina Fanny Hesse

Figure 1. Angelina "Lina" Fanny Hesse. (photo source)

Angelina Fanny Hesse Contributed Agar and Art to Microbiology

Hesse not only contributed agar to microbiology, but she also worked in Koch’s lab as an assistant, much like one of today’s lab technicians, and was a scientific illustrator. Walther used her drawings of his microscopy in his publications. An article written by Hesse’s grandson describes her illustrations of intestinal bacteria for Walther’s 1908 publication as “magnified colonies on agar plates during different growth phases” that were colored “with watercolors in a highly accurate way, indicating her thorough understanding of bacteriology and microscopy.”

Angelina Fanny Hesse, a Name to Recognize

Almost every microbiologist today uses agar to solidify microbiological growth media. So, we wanted to recognize Angelina Fanny Hesse as the woman who contributed agar to microbiology and hope that her name becomes as pervasive as the use of agar.

Learn more about different types of microbiological culture media. If you know what you need, be sure to explore our agar plate options.