Clinical significance of the Streptococcus milleri group in peritonsillar abscesses

Abstract

Few researchers have microbiologically studied peritonsillar abscesses in detail, and their results have been conflicting. Although Streptococcus pyogenes (Group A beta-streptococcus) is commonly considered an important pathogen in this infection, recent studies have demonstrated the recovery of many other streptococci mainly consisting of alpha-streptococci. Few studies have identified these streptococci at the species level, however. We studied details of bacteriology in 31 cases of peritonsillar abscess treated between 1991 and 2000. The Streptococcus milleri group was most frequently isolated (25.8%), followed by Eikenella corrodens (9.7%), Staphylococcus aureus (6.5%), and S. pyogenes (3.2%). The S. milleri group, consisting of 3 species of Streptococcus constellatus, S. intermedius, and S. anginosus, forms part of the normal flora most commonly found in the mouth, throat, gastrointestinal tract, and genital tract. These species have become known as an important pathogen in abscess disease but little attention has been paid to their role in peritonsillar abscesses. To adequately culture the S. milleri group, incubation in air containing carbon dioxide or in an anaerobic condition is required, and then the differentiation of the 3 species requires the biochemical reactivity tests. Since hemolytic patterns of the S. milleri group vary, we studied the population of alpha-, beta-, and gamma-hemolytic strains among 36 strains of this group. We found 32 (88.8%) to be alpha-hemolytic. Although not all alpha-hemolytic strains belong to the S. milleri group, a considerable number of this group could be missed among alpha-streptococci isolated from the peritonsillar abscess. As antibiotics began being used widely, normal flora such as the S. milleri group may have become an important pathogen in peritonsillar abscesses due to an imbalance between organisms and host defense.