Who suggested the use of agar as a culture medium for bacteria?

Fanny Hesse suggested using agar as a culture medium for bacteria.

In the early 1880s, Hesse assisted her husband, Walther Hesse, with laboratory work on bacterial growth media. Gelatin was commonly used to solidify nutrient mixtures, but it melted at roughly body temperature and could also be broken down by gelatin-digesting bacteria. That made it unreliable for growing colonies in warm laboratories.

Hesse knew agar from cooking and preserving foods. The seaweed-derived substance stayed firm at higher temperatures and resisted bacterial enzymes better than gelatin. Her suggestion allowed Walther Hesse and Robert Koch to use a more stable medium for isolating bacterial colonies, including work connected with tuberculosis research.

The credit is sometimes mistakenly given to Robert Koch because he used agar in published experiments, or to Julius Richard Petri because the Petri dish later became the standard container for solid media. Petri’s dish improved the technique, but Fanny Hesse supplied the crucial practical idea that made agar-based culture so useful.