<u>Answer:</u>
<u>D. purple, spherical-shaped organisms arranged in chainlike formation</u>
<u>Explanation:</u>
Streptococcus pyogenes is a gram positive coccus. Coccus implies that it has a spherical shape.
Gram positive organisms like streptococcus pyogenes take up purple stain on gram staining whereas gram negative organisms like E. coli take up pink stain on gram staining.
Further more, streptococcus pyogenes is arranged in chains or pairs. Unlike staphylococcus which is arranged in clusters.
Coming back to answer choices,
<u>A. pink, rod-shaped organisms arranged in pairs</u>
It is the incorrect choice as Streptococcus pyogenes is gram positive and they appear blue on gram staining.
<u>B. purple, spherical-shaped organisms arranged in grapelike clusters</u>
This is the incorrect choice. Although Streptococcus pyogenes appears blue on gram staining but it is arranged in chains like a beaded necklace. Purple, spherical-shaped organisms arranged in grape-like clusters is typical appearance of Staphylococcus.
<u>C. pink, spherical-shaped organisms arranged in chainlike formations</u>
It is incorrect as Streptococcus pyogenes appears blue on gram staining as it is gram positive.
<u>D. purple, spherical-shaped organisms arranged in chainlike formation</u>
This is the correct choice and describes typical appearance of Streptococcus pyogenes.
