Magnified 100x, this image depicted a Petri dish filled with trypticase soy agar medium containing 5% defibrinated sheep's blood, i.e., blood agar plate (BAP). After having been inoculated with alpha-hemolytic Streptococcus anginosus bacteria, i.e., members of the Gram-positive viridans group of streptococci (VGS), just before the blood was added to the agar, a loop of diluted culture was put into the melted agar (50oC). The melted agar with blood was allowed to solidify and then incubated at 35oC for 24 hours in a normal atmosphere. The culture grew subsurface bacterial colonies, one of which was seen here. Surrounded by a characteristic hazy, faded, and indistinct region (arrow) in which some of the red blood cells were destroyed in the agar medium, or "hemolyzed", indicating that these bacteria were indeed alpha-hemolytic in nature.
CDC/ Richard R. Facklam, Ph.D.
November 26, 2012
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