File:Group A streptococcus21.jpeg

This 1977 photograph depicted a Petri dish with Streptococcus pyogenes-inoculated trypticase soy agar containing 5% defibrinated sheep's blood, i.e., blood agar plate (BAP), that had been "streaked", and "stabbed" with a wire loop, which had been dipped into primary culture medium. The BAP was incubated in a normal atmosphere at 35oC for 24 hours. In this case, the culture dish grew colonies of Gram-positive Group A beta-Streptococci (GAS) bacteria. The characteristic color changes, i.e., a clear, colorless region 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. There is no magnification of this image.