Frank Lowy Streptococci and Enterococci

The genus Streptococcus includes a heterogeneous group of different Gram positive species (>30) that are identified on Gram stain by their spherical or ovoid shape and their tendency to grow in pairs and chains. They are nonmotile, non-spore forming, and mostly facultatively anaerobic. Streptococci are a heterogeneous group that includes a variety of species capable of causing a diverse array of different diseases ranging from minor soft tissue infections to life-threatening sepsis. The most important pathogens in this group are Streptococcus pyogenes (group A streptococcus), Streptococcus agalactiae (group B streptococcus) and Streptococcus pneumoniae (pneumococcus). DNA homology studies have established Enterococcus (formerly streptococci) as a separate genus, distinct from Streptococcus. This lecture will cover only two of these pathogens, S. pyogenes and S. pneumoniae. Although not covered in the lecture you are also responsible for S. agalactiae, enterococci and viridans streptococci. The different streptococcal species have different sites of colonization and cause different types of infections. These are described in the table below.