Beta-hemolytic streptococcus with Lancefield Group A. Which organism is this?

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Multiple Choice

Beta-hemolytic streptococcus with Lancefield Group A. Which organism is this?

Beta-hemolysis on blood agar paired with Lancefield Group A identically points to Streptococcus pyogenes. Beta-hemolysis means complete clearing around colonies due to red blood cell lysis, and Lancefield grouping classifies streptococci by a C carbohydrate antigen in the cell wall. Group A is the designation for the Streptococcus species that is most classically associated with this pattern, namely S. pyogenes, a common human pathogen responsible for illnesses like strep throat and skin infections. Other organisms listed have different patterns or groupings: for example, Group B streptococci are beta-hemolytic but belong to Streptococcus agalactiae, while Streptococcus pneumoniae and Streptococcus mitis are typically alpha-hemolytic and not Group A.

Beta-hemolysis on blood agar paired with Lancefield Group A identically points to Streptococcus pyogenes. Beta-hemolysis means complete clearing around colonies due to red blood cell lysis, and Lancefield grouping classifies streptococci by a C carbohydrate antigen in the cell wall. Group A is the designation for the Streptococcus species that is most classically associated with this pattern, namely S. pyogenes, a common human pathogen responsible for illnesses like strep throat and skin infections. Other organisms listed have different patterns or groupings: for example, Group B streptococci are beta-hemolytic but belong to Streptococcus agalactiae, while Streptococcus pneumoniae and Streptococcus mitis are typically alpha-hemolytic and not Group A.

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