The history of blood agar, as we know it today, is uncertain. The inclusion of blood as a nutritive supplement in culture media may pre-date the use of agar. In their 1903 Manual of Bacteriology, Muir and Ritchie list its inclusion before they discuss “agar-agar” as a replacement for gelatin as a solidifying agent.
In the same discussion, however, they note that Robert Koch preferred plates poured by mixing bacterial inocula with melted gelatin rather than streaking material on the surface. Koch recommended media that were “firm, and where possible, …transparent…” It appears that pour plates were the standard procedure for many years due largely to problems with surface contamination upon incubation. (It should be noted that, initially, agar “plates” were, indeed, sterilized flat glass plates, not Petrie dishes as we know today.)
An interesting method of adding blood to agar media is described in Bulloch’s 1938 The History of Bacteriology:
Human blood or the blood of animals may be used. “Sloped tubes” of agar are employed. …Purify a finger first with 1-1000 corrosive sublimate, dry, and then wash with absolute alcohol to remove the sublimate. Allow the alcohol to evaporate. Prick with a needle sterilised by heat, and, catching a drop of blood in the loop of a sterile platinum wire, smear it on the surface of the agar. The excess of the blood runs down and leaves a film on the surface. Cover the tubes with India-rubber caps, and incubate them for one to two days at 37°C before use, to make certain that they are sterile. Agar poured out in a thin layer in a Petri dish may be smeared with blood in the same way and used for culture. In investigating the diseases of races other than the white, it appears advisable to use the blood of the race under investigation.
Any reader interested in the history of microbiology should explore Wolfgang Hesse’s biographical sketch of his grandparents, Walther and Angelina (“Lina”) (below). Walther was a protégé of Koch, and Angelina served as his assistant and illustrator. Sometime prior to the end of 1882, Walther was frustrated by the melting of his gelatin-coated culture tubes in the summer heat. He quizzed Lina about her jellies and puddings which maintained their solid consistency even at the warm temperatures. It seems that she had learned about the use of agar from a former neighbor (who had emigrated from Java where agar was a common food additive). Although there is no written record of such, it could easily be imagined that Walther stirred blood into his cooled, melted agar in the same way that Lina did her fruit and meat juices!
(Rebecca Buxton with archival help from Jeff Karr)
ASM News article "Walther and Angelina Hesse - Early Contributors to Bacteriology" by Wolfgang Hesse and translated by Dieter H. M. Groschel (1992).
The history of blood agar, as we know it today, is uncertain. The inclusion of blood as a nutritive supplement in culture media may pre-date the use of agar. In their 1903 Manual of Bacteriology, Muir and Ritchie list its inclusion before they discuss “agar-agar” as a replacement for gelatin as a solidifying agent.
In the same discussion, however, they note that Robert Koch preferred plates poured by mixing bacterial inocula with melted gelatin rather than streaking material on the surface. Koch recommended media that were “firm, and where possible, …transparent…” It appears that pour plates were the standard procedure for many years due largely to problems with surface contamination upon incubation. (It should be noted that, initially, agar “plates” were, indeed, sterilized flat glass plates, not Petrie dishes as we know today.)
An interesting method of adding blood to agar media is described in Bulloch’s 1938 The History of Bacteriology:
Human blood or the blood of animals may be used. “Sloped tubes” of agar are employed. …Purify a finger first with 1-1000 corrosive sublimate, dry, and then wash with absolute alcohol to remove the sublimate. Allow the alcohol to evaporate. Prick with a needle sterilised by heat, and, catching a drop of blood in the loop of a sterile platinum wire, smear it on the surface of the agar. The excess of the blood runs down and leaves a film on the surface. Cover the tubes with India-rubber caps, and incubate them for one to two days at 37°C before use, to make certain that they are sterile. Agar poured out in a thin layer in a Petri dish may be smeared with blood in the same way and used for culture. In investigating the diseases of races other than the white, it appears advisable to use the blood of the race under investigation.
Any reader interested in the history of microbiology should explore Wolfgang Hesse’s biographical sketch of his grandparents, Walther and Angelina (“Lina”) (below). Walther was a protégé of Koch, and Angelina served as his assistant and illustrator. Sometime prior to the end of 1882, Walther was frustrated by the melting of his gelatin-coated culture tubes in the summer heat. He quizzed Lina about her jellies and puddings which maintained their solid consistency even at the warm temperatures. It seems that she had learned about the use of agar from a former neighbor (who had emigrated from Java where agar was a common food additive). Although there is no written record of such, it could easily be imagined that Walther stirred blood into his cooled, melted agar in the same way that Lina did her fruit and meat juices!
(Rebecca Buxton with archival help from Jeff Karr)
ASM News article "Walther and Angelina Hesse - Early Contributors to Bacteriology" by Wolfgang Hesse and translated by Dieter H. M. Groschel (1992).
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