What findings in a throat culture would indicate strep throat?

• A. Negative beta-hemolytic streptococcus
• B. Positive beta-hemolytic streptococcus
• C. Presence of a viral infection
• D. High levels of white blood cells

Answer: (B)

Strep throat is diagnosed when the throat culture shows beta-hemolytic Streptococcus. On a blood agar plate, this organism fully lyses red blood cells around its colonies, creating a clear zone called beta-hemolysis. That specific pattern points to group A Streptococcus, the usual cause of strep throat, making it the strongest indicator in the culture. If there’s no beta-hemolysis, or if the hemolysis is only partial (alpha) or none (gamma), it’s not consistent with strep throat. A viral infection wouldn’t produce a beta-hemolytic bacterial colony on culture, and high white blood cell counts are a general sign of infection but don’t pinpoint a culture finding for strep throat.