ID#: 8178
This 1977 image depicts a Petri dish filled with trypticase soy agar medium containing 5% defibrinated sheep's blood. Using a streak/stab technique, the agar was inoculated with alpha-hemolytic, Streptococcus anginosus bacteria, a member of the Gram-positive viridans group of streptococci (VGS), then incubated in a carbon dioxide enriched atmosphere at 35oC for 24-hours. The culture grew typical alpha-hemolytic bacterial colonies adjacent to the stab sites (arrow). The hazy, indistinct region surrounding each colony indicated that red blood cells (RBCs) had been destroyed, or hemolyzed, and that these bacteria were indeed alpha-hemolytic in nature. It is the incomplete nature of the hemolytic reaction adjacent to the colonies, which spares numbers of RBCs in the blood agar medium that classifies these bacteria as alpha-hemolytic, and not beta-hemolytic, in which case the RBCs are completely destroyed.
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Content Provider(s): CDC/ Richard R. Facklam, Ph.D.
Creation Date: 1977
Photo Credit:
CDC Organization
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Copyright Restrictions: None - This image is in the public domain and thus free of any copyright restrictions.