Magnified 100x, this 1977 photograph 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 Group A Streptococcus pyogenes (GAS) bacteria using a wire loop stab technique, the BAP was incubated in a carbon dioxide enriched atmosphere at 35oC for 24 hours. The culture grew bacterial colonies along the edge of the stab, a number of which were seen here. The characteristic color changes, i.e., a colorless region around the stabbed area containing colonies of GAS 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.Infection with GAS can result in a range of symptoms:- No illness- Mild illness (strep throat or a skin infection such as impetigo)- Severe illness (necrotizing faciitis, streptococcal toxic shock syndrome)
CDC/ Richard R. Facklam, Ph.D.
November 27, 2012
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