"Streptococcus milleri" bacteria comprise 3 distinct species: Streptococcus intermedius, S. constellatus, and S. anginosus. Speciation of "S. milleri" isolates is technically difficult and is not undertaken by most clinical laboratories. Although the group has been associated with abscesses, the association may not be causal for all 3 species.
Investigators used biochemical tests and 16S RNA sequencing to speciate 122 clinical isolates of "S. milleri" obtained at a Veterans Affairs medical center during 1 year. S. intermedius accounted for only 11 percent of the isolates, but 86 percent of these were isolated either from an abscess, or from blood or CSF associated with an abscess. S. constellatus accounted for another 46 percent of the isola…