Blood Agar Plates and Hemolysis Protocols

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.)

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Blood Agar Plates and Hemolysis Protocols

Source: ASM microbe library
Image credits: Budon

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