What characteristic distinguishes Streptococcus pneumoniae from other streptococci?

The distinction of Streptococcus pneumoniae from other streptococci primarily lies in its α-hemolytic characteristics. This organism is known for its ability to partially lyse red blood cells on blood agar, leading to a greenish discoloration around the colonies. This hemolytic behavior is significant because it is one of the primary traits utilized in the laboratory to identify and differentiate S. pneumoniae from non-pathogenic streptococci, as well as from β-hemolytic streptococci, which completely lyse red blood cells and produce a clear zone around colonies.

Additionally, while S. pneumoniae is catalase-negative (not able to produce catalase) and exhibits susceptibility to bacitracin—the latter being a trait that distinguishes it fromGroup A streptococci—these factors do not define its uniqueness among streptococci in the same way that its α-hemolysis does. The specific hemolytic activity is a critical component of its identification in clinical settings and serves as an essential characteristic of this bacterium.