Streptococcus

            Gram positive, catalase negative, nonsporing, spherical or ovoid cells. Cell division occurs in one plane, therefore, they are arranged in pairs or chains. Most strains produce capsules composed of hyaluronic acid. Generally nonmotile. Majority are aerobes and facultative anaerobes, some are obligate anaerobes, some require CO₂ for growth. Also growth can be enhanced by the addition of glucose, blood or serum. Their G + C content is 30 – 46 mol%. Streptococci form normal flora of man and animals. They inhabit respiratory tract, live harmlessly as commensals.

Important disease causing species are : Streptococcus pneumoniae

                                                          Streptococcus pyogenes

                                                         Streptococcus mutans