Which organism is a Gram-positive coccus in chains and is PYR positive and typically non-hemolytic on blood agar?

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Multiple Choice

Which organism is a Gram-positive coccus in chains and is PYR positive and typically non-hemolytic on blood agar?

The key idea is using how the organism looks on a slide and how it behaves on blood agar and in a simple biochemical test to identify it. A Gram-positive coccus that tends to appear in chains and is positive for the PYR test, while not producing a clear zone of hemolysis on blood agar, points to Enterococcus species. Enterococci are Gram-positive cocci that commonly occur in pairs or short chains, and they are PYR positive. On blood agar, they are usually gamma-hemolytic (non-hemolytic), though some strains can show alpha or weak beta hemolysis in certain conditions. Additional confirming traits include their ability to grow in bile and in 6.5% NaCl, but the question emphasizes the chain-like arrangement together with PYR positivity and non-hemolysis. Streptococcus pyogenes also forms chains and is PYR positive, but it characteristically shows beta-hemolysis on blood agar. Streptococcus pneumoniae appears as Gram-positive diplococci and is typically alpha-hemolytic, not PYR positive. Staphylococcus aureus forms cocci in clusters rather than chains, and is catalase-positive, which sets it apart from the chain-forming streptococci.

The key idea is using how the organism looks on a slide and how it behaves on blood agar and in a simple biochemical test to identify it. A Gram-positive coccus that tends to appear in chains and is positive for the PYR test, while not producing a clear zone of hemolysis on blood agar, points to Enterococcus species. Enterococci are Gram-positive cocci that commonly occur in pairs or short chains, and they are PYR positive. On blood agar, they are usually gamma-hemolytic (non-hemolytic), though some strains can show alpha or weak beta hemolysis in certain conditions. Additional confirming traits include their ability to grow in bile and in 6.5% NaCl, but the question emphasizes the chain-like arrangement together with PYR positivity and non-hemolysis.

Streptococcus pyogenes also forms chains and is PYR positive, but it characteristically shows beta-hemolysis on blood agar. Streptococcus pneumoniae appears as Gram-positive diplococci and is typically alpha-hemolytic, not PYR positive. Staphylococcus aureus forms cocci in clusters rather than chains, and is catalase-positive, which sets it apart from the chain-forming streptococci.

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