What differentiates virulent strains of Streptococcus pneumoniae from nonvirulent strains?
A) the species-specific teichoic acid present in its cell wall
B) the type of Lancefield antigen it produces
C) the presence of a polysaccharide capsule
D) the type of toxins it produces
E) the extent of the hemolytic zone it produces when it is grown on blood agar

Question

Quizplus · Accepted Answer

The polysaccharide capsule is the main virulence factor for Streptococcus pneumoniae, as it protects the bacteria from phagocytosis by host immune cells. Nonvirulent strains of S. pneumoniae usually lack a capsule or have a very thin capsule, while virulent strains have a thick capsule composed of different types of polysaccharides.

Answer choices A, B, D, and E are not accurate differentiators between virulent and nonvirulent strains of S. pneumoniae. Teichoic acid and Lancefield antigens are components of the bacterial cell wall that are not directly linked to virulence. The type of toxins produced by S. pneumoniae can vary among strains, but they are not the main virulence factor. The extent of the hemolytic zone produced on blood agar is a characteristic used to differentiate Streptococcus species based on their ability to lyse red blood cells, but it is not specific for virulence within the same species.

What Differentiates Virulent Strains of Streptococcus Pneumoniae from Nonvirulent Strains