Streptococcus anginosus Group Bacteria: No Longer a Case of Mistaken Identity

The anginosus, or “milleri,” group of bacteria belonging to the genus Streptococcus have long been the cause of much consternation with respect to both their nomenclature and accurate laboratory identification. Although they are considered part of the normal flora of the human gastrointestinal, urogenital, and upper respiratory tracts, Streptococcus anginosus group (SAG) bacteria have the ability to cause severe invasive infections with a propensity for abscess formation. Although whole-genome and multilocus sequence analyses of SAG bacteria support the current view that the SAG is made up of three distinct species (S. anginosus, S. constellatus, and S. intermedius) and a number of subspecies, advances in molecular technology have allowed more accurate laboratory identification of SAG bacteria; it remains to be seen whether distinguishing these species and subspecies will be of clinical importance.