Final answer:
Streptococcal pharyngitis is caused by Streptococcus pyogenes, scarlet fever by the same bacterium that produces an erythrogenic toxin, and pneumococcal pneumonia by Streptococcus pneumoniae; all are classified by Lancefield groups.
Step-by-step explanation:
The three diseases caused by the three species of Streptococcus are:
- Streptococcal pharyngitis (strep throat), caused by Streptococcus pyogenes (Group A strep)
- Scarlet fever (or scarlatina), which is also caused by certain strains of Streptococcus pyogenes that produce an erythrogenic toxin
- Pneumococcal pneumonia, caused by Streptococcus pneumoniae
Streptococcus pyogenes is known for causing strep throat, scarlet fever, and potentially leading to streptococcal toxic shock syndrome (STSS), while Streptococcus pneumoniae is associated with causing pneumococcal pneumonia. These bacterial species are classified by Lancefield groups and can exhibit different symptoms ranging from respiratory tract infections to skin rashes.