Final Diagnosis -- Multiple Brain Abscesses Caused by Streptococcus Milleri Group: S. intermedius.

FINAL DIAGNOSIS: - Multiple brain abscesses caused by Streptococcus milleri group: S. intermedius.

Contributor's notes:
"Streptococcus milleri" was first named by Guthof in 1956 in reference to oral non-hemolytic streptococcal species (1) . Subsequently, Colman and Williams proposed that minute beta-hemolytic streptococci along with other non-hemolytic streptococci referred to as the "streptococcus milleri group" (2). Conkendall proposed the unification of these streptococci into a single species Streptococcus anginosus which was the oldest approved name for these bacteria and therefore had precedence over the name "streptococcus milleri"(3). Recently, Whiley et al performed DNA relatedness studies on strains classified as Streptococcus anginosus, and observed that three DNA homology groups could be identified that correspond to the type strains of Streptococcus constellatus, Streptococcus intermedius and Streptococcus anginosus. Based on the DNA studies, the milleri group has been recently reclassified into three distinct strains: S. constellatus, S anginosus, and S intermedius (4).

The species of streptococcus milleri group are commensals commonly isolated from the mouth, oropharynx, gastrointestinal tract and vagina, and are responsible for a variety of human and animal infections (5). Predisposing or underlying conditions were noted in most of reported cases of S. milleri infection. The most common conditions were previous surgery, trauma, diabetes, immunodeficiency, malignancy, and prosthetic device. The species of S.milleri group are in varies type of infections characterized by deep tissue necrosis and abscesses formation, either along or in mixed culture. Most of the reported cases of S. milleri infection are associated with following sites or organs:

  1. deep-seated, necrotic odontogenic abscess.
  2. purulent empyema or lung abscess.
  3. abdominal and hepatic abscess
  4. brain abscess.
  5. Menigitis, acute epidural abscess, and subdural abscess.
  6. Endocarditis and myocardial abscess.
  7. Obstetrical infections and neonatal sepsis.
The mechanisms by which the S. milleri group are pathogenic are unclear. It is thought that extracellular enzymes produced by these organisms may contribute to its pathogenicity by degradation og connective tissue. These enzymes include hyaluronidase deoxyribonuclease, ribonuclease, gelatinase and collagenase. The S. milleri group also releases an immnusupressive subtances which has not been characterized. This unidentified substance may promote pathogenicity and allow the organismsto survive with an abscess. IStudies in a mouse model of pneumonai demonstrate S. milleri group organisms are susceptible to wide range of antibiotics including penicillins, cephalosporins, clindamycin, vancomycin and erythromycin. Surgical evacuation is often necessary for bacterial eradication.

Although the S. milleri group organisms have received increasing attentions as potential pathogen in above mentioned infections, their role in these serious infections remains largely unrecognized. There are several explanations for this lack of recognition. First, it may due to the long period of confusion regarding streptococcal taxonimy and nomenclature. Second, the clinical microbiological characteristics of the S. milleri group may lead to misidentification. Third, the use of antibiotics before the collection of sample for analysis may greatly affect the results. Better understanding of the bacteriologic features, pathogenicity, and epidemiology of the S. milleri group should aid clinicians in recognizing and treating properly with this elusive pathogen.


  1. Guthof O: Uber pathogene "vergrunends Streptokokken". Streptokokken-Befunde bei dentogenen Abszessen und infiltraten im bereich der Mundhohle. Zentralblatt fur Bakteriologie, Parasitenkunde, Infektionskrankheiten, Hygiene 1956, 166:553-564.
  2. Colman G, Williams REO: Taxonomy of some human viridans streptococci. In: Wannamaker LW, Matsen JM (ed): Streptococci and streptococcal diseases: recognition, understanding, and management. Academic Press, New York, 1972, P. 281-299.
  3. Coykendall AL, Wesbecher PM, Gustafson KB: Streptococcus milleri, Streptococcus constellatus, and Streptococcus intermedius are later synonyms of Streptococcus anginosus. International Journal of Systematic Bacteriology 1987, 37: 222-228.
  4. Whiley RA, Hardie JM: DNA-DNA hybridization studies and phenotypic characteristics of strains within the Streptococcus milleri group. Journal of General Microbiology 1989, 135: 2623-2633.
  5. Whiley RA, Beighton D: Emended descriptions and recognition of Streptococcus constellatus, Streptococcus intermedius and Streptococcus anginosus as distinct species. International Journal of Systematic Bacteriology 1991, 41: 1-5.

Contributed by Jianzhou Wang, MD., and A. William Pasculle, Sc.D.


IndexCME Case StudiesFeedbackHome