Streptococci belonging to groups C, F, and G, and rarely H, K, O, and R can also be associated with human infections.
Group C streptococci are usually pathogens of animals. Streptococcus equisimilisis a group C Streptococcus, which can cause occasional infections in humans. S. equisimilis resembles S. pyogenes in fermenting trehalose but differs from it by notfermenting ribose. Like S. pyogenes, it also produces SLO, strep-tokinase, and other proteins. It causes upper respiratory tract infections and also pneumonia, osteomyelitis, endocarditis, brain abscess, and puerperal sepsis.
S. equisimilis shows tolerance to treatment with penicillin;therefore patients may not respond to treatment with penicillin.
These cocci are called “minute streptococci”. They grow on blood agar well in the presence of CO2. Streptococcus MG is a member of this group that can cause primary atypical pneumo-nia in humans. Demonstration of cold agglutinins in serum is diagnostic of primary atypical pneumonia.
Group G streptococci are the commensals of humans and of animals, such as monkeys and dogs. They may occasionally cause infections, such as tonsillitis, urinary tract infection, and endocarditis in humans.
Streptococcus bovis and Streptococcus equinus are the nonentero-coccal group D streptococci, which are associated with human infections, such as urinary tract infections and rarely endocar-ditis. They are susceptible to penicillins.