Which statement about the size of Streptococcus pyogenes cocci is correct?

• A. 0.2-0.4 micrometers
• B. 2-3 micrometers
• C. 5-10 micrometers
• D. 0.6-1.0 micrometers

Answer: (D)

Streptococcus pyogenes are small spherical bacteria (cocci) with a typical diameter of about 0.6–1.0 micrometers. This size fits the common scale for cocci seen under standard light microscopy and explains why they appear as tiny beads that can form chains. The other size ranges don’t match the usual dimensions of this organism: 0.2–0.4 μm would be smaller than most cocci, while 2–3 μm or 5–10 μm would be larger than typical cocci like Streptococcus. Recognizing this size range helps connect how these bacteria look in bright-field images and why they’re resolved as small spherical units.