Which organism is typically beta-hemolytic, catalase negative, PYR positive, and belongs to Lancefield group A?

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Multiple Choice

Which organism is typically beta-hemolytic, catalase negative, PYR positive, and belongs to Lancefield group A?

Beta-hemolysis on blood agar indicates complete lysis of red blood cells around the colonies, a pattern seen with certain streptococci. Because the organism is catalase negative, it is not a staphylococcus. A positive PYR test is a hint toward group A streptococci and helps distinguish them from other beta-hemolytic streptococci. The Lancefield group A designation refers to the specific C carbohydrate in the cell wall found in Streptococcus pyogenes. Taken together, this combination identifies Streptococcus pyogenes. (Others like S. pneumoniae are typically alpha-hemolytic, and Staphylococcus aureus is catalase positive, while Enterococcus faecalis is usually group D and not the Group A profile.)

Beta-hemolysis on blood agar indicates complete lysis of red blood cells around the colonies, a pattern seen with certain streptococci. Because the organism is catalase negative, it is not a staphylococcus. A positive PYR test is a hint toward group A streptococci and helps distinguish them from other beta-hemolytic streptococci. The Lancefield group A designation refers to the specific C carbohydrate in the cell wall found in Streptococcus pyogenes. Taken together, this combination identifies Streptococcus pyogenes. (Others like S. pneumoniae are typically alpha-hemolytic, and Staphylococcus aureus is catalase positive, while Enterococcus faecalis is usually group D and not the Group A profile.)

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