Discovery of Agar as a Solidifying Agent

The earliest culture media were liquid, which made the isolation of bacteria to prepare pure cultures extremely difficult. In practice,a mixture of bacteria was diluted successively until only one organism, as an average, was present in a culture vessel. If everything went well, the individual bacterium thus isolateb would reproduce to give a pure culture. This approach was tedious, gave variable results, and was plagued by contamination problems. progress in isolating pathogenic bacteria understandably was slow.
The development of techniques for growing microorganisms on solid media and efficiently obtaining pure cultures was due to the efforts of the German bacteriologist Robert Koch and his associates. In 1881, Koch published an article describing the use of boiled potatoes, sliced with a flame sterilized knife, in culturing bacteria. The surface of a sterils slice of potato was inoculated with bacteria from a needle tip, and then the bacteria were streaked out over the surface so that a few individual cells would be separated from the remainder. The slices were incubated beneath bell jars to prevent airborne contamination, and the isolated cells developed into pure colonies. Unfortunately, many bacteria would not grow well on potato slices.
At about the same time, Frederick Loeffler, an associate of Koch, developed a meat extract peptone medium for cultivating pathogenic bacteria. Koch decided to try solidifying this medium. Koch was an amateur photographer – he was the first to take photomicrographs of bacteria – and was experienced in preparing his own photographic plates from silver salts and gelatin. Precisely the same approach was employed for preparing solid media. He spread a mixture of Loeffler’s medium and gelatin over a glass plate, allowed it to harden, and inoculated the surface in the same way he had inoculated his sliced potatoes. The new solid medium worked well, but it could not be incubated at 37 Degree C because the gelatin would melt. Furthermore, same bacteria digested the gelatin.
About a year later, in 1882, agar was first used as a solidifying agent. It had been discovered by a Japanese innkeeper, Minora Tarazaemon. The story goes that he threw out extra seaweed soup and discovered the next day that it had gelled during the cold winter night. Agar had been used by the East Indies Dutch to make jellies and jams. Fannie Eilshemius Hesse, the New Jersey – born wife of Walther Hesse, one of Koch’s assistants, had learned of agar from a Dutch acquaintance and suggested its use when she heard of the difficulties with gelatin. Agar – solidified medium was an instant success and continues to be essential in all areas of microbiology.

Source – Presscott, Harley, and Klein’s Microbiology.


One Response

  1. the site gives a concise discovery of Agar

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