Strep bacteria Streptococcus is a genus of spherical (coccus) bacteria that, because of the way they divide, grow in chains, from pairs to long chains of multiple organisms. There are over 50 different species that have been identified. Some of them cause health problems in humans ranging from dental caries (S. mutans typically) to pneumonia (S. pneumoniae). One species in particular, S. pyogenes, is implicated in a wide variety of severe disease from toxic shock syndrome, t