Classification and overview of the genera Streptococcus and Enterococcus

The genera Streptococcus and Enterococcus both consist of Gram-positive, spherical or ovoid cells which are typically arranged in pairs or chains. They are non-sporing, facultatively anaerobic, catalase negative, homofermentative, and have complex nutritional requirements. As described below, they were for many years considered to belong to the same genus (Streptococcus), but are now clearly recognized as being distinct, alongside a number of other genera of lactic acid bacteria (LAB) (Schleifer and Ludwig 1995). The 40 or so currently recognized species of Streptococcus and 17 species of Enterococcus are widely distributed, mainly on mucosal surfaces of man and animals, including the gastrointestinal tract, but some are also found in soil, water, dairy products and other foods, and on plants. Some species, such as Streptococcus pyogenes and Strep. pneumoniae, are well-recognized as major human pathogens and many of the others are capable of causing disease under appropriate circumstances. Similarly, there are many species within these genera which are responsible for significant levels of disease in domestic, farm and aquatic animals (Devriese and Pot 1995; Hardie and Whiley 1995).