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Comparison of alpha and beta hemolysis

Two Petri dishes, each filled with trypticase soy agar medium, containing 5% defibrinated sheep's blood. The plate on the left had been stabbed and streaked with an inoculum containing Streptococcus mitis, alpha-hemolytic bacteria, a member of the Viridans group, while the right plate was stabbed with an inoculum containing Group A Streptococcus pyogenes (GAS), a typical beta-hemolytic bacteria. The inoculation was performed using a wire loop, which had been dipped into a primary culture medium. The blood agar plates were incubated in a carbon dioxide-enriched atmosphere at 35°C for 24 hours. All culture organisms were Gram-positive cocci. The alpha-hemolytic organisms on the left plate grew colonies that were surrounded by a hazy, indistinct zone of partial red blood cell (RBC) hemolysis, and the beta-hemolytic bacteria on the right grew colonies surrounded by a clear, colorless zone of complete RBC destruction. Using the "stabbing" method of inoculation makes the qualitative interpretation of the hemolytic reaction much easier, for the results of colonial interactivity with the blood agar medium are much more pronounced, and therefore, easier to discern. (Source: CDC/Dr. Richard R Facklam, 1977. Public Health Image Library, Centers for Disease Control and Prevention, Atlanta, Georgia. Public domain.)

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