A 20-year-old female presents with pharyngitis. The rapid group A Streptococcus screen is negative, and a blood agar plate is inoculated. After 24 hours incubation, a tiny gray colony with a narrow zone of beta-hemolysis is observed. The microbiologist performs a streptococcal serotype for group A and the result is negative. She should

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The presence of tiny gray colonies with a narrow zone of beta-hemolysis suggests a Streptococcus species, but the negative result for group A Streptococcus serotyping indicates it might be another type of Streptococcus or a different Gram-positive organism. Performing a Gram stain will confirm if the organism is Gram-positive (as expected for Streptococcus species) and the catalase test will differentiate Streptococcus (catalase-negative) from other Gram-positive cocci like Staphylococcus (catalase-positive).

A 20-Year-Old Female Presents with Pharyngitis