[Clinical relevance of the Streptococcus milleri group in head and neck infections]

Abstract

Streptococcus constellatus, S. intermedius, and S. anginosus, the 3 species of the S. milleri group, form part of the normal flora commonly found in the mouth, throat, and gastrointestinal and genital tracts. This group has become known as an important pathogen in infections and abscesses, but data on the anatomical distribution of these species is lacking in relation to clinical significance. We obtained 275 strains of the S. milleri group from different departments at our hospital over the last 3 years, including 54 strains from dental surgery, 47 from internal medicine, 44 from otolaryngology (head and neck), 43 from surgery, 32 from gynecology, 17 from urology, 16 from dermatology, 11 from brain surgery, 6 from pediatrics, 3 from orthopedics, and 2 from opthalmology. The 44 strains from head and neck were found in 42 patients,--23 with primary infection and 19 with secondary infection induced by cancer treatments. The primary infection group included 4 deep neck abscesses, 1 peritonsillar abscess, 5 tonsillitis, 4 paranasal sinusitis, 3 congenital aural fistula infections, 2 dental infections, 2 paranasal sinus cysts, 1 supprative parotitis, and 1 postoperative wound infection. The secondary infection group included 7 postoperative wound infections, 3 postoperative pulmonary infections, 3 laryngitis and pharyngitis, 3 terminal pneumonias, and 3 infections of the local recurrence site. The S. milleri group was the only isolated organism in 13 cases (56.5%) of primary infection and in 5 (26.3%) of secondary infection. Among other organisms from the primary infection group, no so-called major pathogens were found. Antimicrobial susceptibility tests of the S. milleri group showed that 50% were resistant to CCL and 33% to CTM. ABPC, CPDX, and CFDN were also found to be less sensitive, although no resistant strains were detected. To adequately culture the S. milleri group, incubation in air containing carbon dioxide or in an anaerobic atmosphere is required, and differentiation of the 3 requires biochemical reactivity tests. Since not all facilities use identical techniques in routine bacteriological examination, a considerable number of the S. milleri group could be missed in unknown species of alpha-,beta-, and gamma-streptococci and culture-negative cases. With antibiotics now being used widely, normal flora such as the S. milleri group may have become an important pathogen in head and neck infections due to an imbalance between organisms and host defense.