Streptococcus pyogenes

Streptococcus zooepidemicus (Group C Streptococcus) is an animal-associated pathogen — common in horses and other livestock — that can occasionally cause zoonotic infections in humans, particularly through consumption of…

Clostridium perfringens is a spore-forming bacterium recognized as a common cause of food poisoning and gas gangrene, and is not a probiotic organism.

Streptococcus agalactiae (Group B Streptococcus, or GBS) is a pathogenic bacterium — not a probiotic organism — clinically significant as a leading cause of neonatal infections and a complication of pregnancy.

Streptococcus pneumoniae (the pneumococcus) is a commensal bacterium of the upper respiratory tract that can cause serious opportunistic infections — including pneumonia, meningitis, and septicemia — particularly in immu…

Streptococcus salivarius (undesignated strain) is a species native to the human oral cavity and upper respiratory tract, where it is one of the first bacteria to colonize at birth.

Streptococcus mutans is the primary bacterial species associated with dental caries (tooth decay); it is a well-characterized oral pathogen, not a probiotic organism.