The history of using agar as a coagulant

Everyone doing research on microorganisms knows about environmental coagulants such as agar, agarose, gelatin, gellan gum . and their use characteristics, but the history of agar use is not everyone. clearly.

The medium used to cultivate microorganisms in the early period is not solid, but liquid. This makes the isolation and culture of pure cultures difficult, and there is no concept of colony morphology, a very important indicator of microbiology. At that time to get the pure strain, one must always hope that the dilution process to one cell goes smoothly, and you can imagine how hard it is to get pure strain and fatigue. The trouble with using liquid media slows down the process of isolating and studying new strains of pathogenic bacteria at that time.

The development of environmental dispensing techniques is about to cross a new twist when the first solid environmental concept was invented in 1881 by Robert Koch, a famous German microbiologist. He published an article describing how to use potato slices cut by sterile knives to isolate some microorganisms and show the usability of this method. At that time, the implantation technique was also used for the first time by Koch, he used his head

Robert Koch (Photo: Parazyt.gower.pl)

The whiskers on the potato face and found that there are loose cell colonies, the isolation of pure strains from these colonies is much simpler than the dilution. The potato pieces are then placed in a sealed bell to avoid tap contamination .

However, after only a short time, Koch found that there are many types of bacteria that do not grow on potato slices.

At that time, the pepton high medium was developed by a partner of his, Frederick Loeffer, to grow pathogenic bacteria effectively. Koch immediately set a goal to solidify this kind of environment.

Koch is an amateur photographer, the first to photograph bacteria and is also very knowledgeable in washing photos using silver salts and gelatin . The first thing he thought about was to try to combine Loeffer's environment and gelatin by mixing and pouring on a glass plate, waiting for it to coagulate and then cultivate like potato slices. And once again, gelatin does freeze the environment, but its effect does not make Koch happy because the environment melts at 37 degrees Celsius, an optimal temperature of the bacteria that causes disease in animals, and much more. microorganism decomposes gelatin to loosen the environment. Koch had to look for new coagulants.

A year later, in 1882, the solid environment was frozen with agar born in an accident. Walther Hess (a partner of Koch) complained about the gelatin badness as well as the fact that Koch was looking for a new coagulant with his wife, Fanie Eilshemius Hess, a New Jersey coastal resident. She suggested that they use agar, a coagulant that she used to make jam or vegetables. And the results are unexpected because the agar not only solidifies at temperatures below 40 but also does not degrade microorganisms.

The agar-free environment since its inception has become something important.

Reference : Lansing M. Prescott, John P.Harley, Donald A. Klein 1999.Microbiology 4th Edition.McGraw-Hill.ISBN: 0-697-35439-3.Page 107

Nguyen Huu Hoang