Classification and clinical significance of Streotococcus milleri

One of the reasons why many microbiologists and clinicians have been interested in Streptococcus milleri is that the streptococcus is not only part of the human commensals found in the mouth, nasopharynx, throat, gastrointestinal tract and genitourinary tract, but also has frequently been isolated from a wide variety of human infections, particulary from suppurative lesions. Another reason is that taxonomy and nomenclature of S milleri have been confused. Colman and Williams have claimed that S. milleri could be classified as one of viridans streptococci, whereas Facklam has not agreed the epithet S. milleri and proposed two approved names by lactose fermentation. Since then, many taxonomies and nomenclatures have been proposed by many researchers. Recently, S, milleri was genotypically classified into three distinct taxa, I.e. S. intermedius, S. constellatus, and S. anginosus, and this would be the last word on the taxonomy of S. milleri. Some S. milleri isolates caused dental caries, submandibular and subcutaneous abscess, and endocarditis in experimental animals, although the virulence factors of S. milleri have not been fully ascertained. Considering that S. milleri would be classified into the three approved species, the pathogenic mechanisms of the streptococci and possible associations between the approved species and specific infections will need to be studied in order to enhance the better understanding of the clinically significant streptococci