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Culture of Streptococcus pyogenes (Group A beta-hemolytic Streptococcus) bacteria on soy agar containing 5% defibrinated sheep's blood

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Petri dish with Streptococcus pyogenes-inoculated trypticase soy agar containing 5% defibrinated sheep's blood that had been streaked and stabbed with a wire loop, which had been dipped into primary culture medium. The blood agar plate (BAP) was incubated in a normal atmosphere at 35°C for 24 hours. In this case, the culture dish grew colonies of Gram-positive, Group A beta-hemolytic streptococci ("GAS") bacteria. The characteristic color changes, including a light-colored halo surrounding each colony in which the red blood cells in the blood agar medium had been destroyed, or hemolyzed, indicated that these bacteria were indeed beta-hemolytic in nature. (Courtesy of the Centers for Disease Control and Prevention Public Health Image Library. Image 8170. Photograph by Dr. Richard R Facklam, CDC, 1977. Public domain.)