Is a mesophilic alpha-hemolytic species of Streptococcus that inhabits the human mouth. It is most commonly found in the throat, nasopharynx, and mouth. It is a Gram-positive coccus, facultative anaerobe and catalase negative. It can cause infective endocarditis. S. mitis cells are able to take up exogenous DNA and incorporate exogenous sequence information into their genome by homologous recombination. These bacteria can employ a predatory fratricidal mechanism for active acquisition of homologous DNA.