ORAL MICROBIOLOGY
Figure 1. The most frequent clinical signs and
symptoms found in brain abscess cases
and seldom from blood, abscess or different intraabdominal infections. The strains of this subspecies
are beta-haemolytic, belong to Lacefield group C
and produce larger haemolytic zones compared to
S. constellatus subsp. pharyngis and viborgensis.
The isolates of S. constellatus subsp. viborgensis
have been isolated from the pharynx, are betahaemolytic and carry the Lancefield group C
antigen.3
The Anginosus streptococci colonizing the mouth,
pharynx, genitourinary and intestinal tract can
cause severe opportunistic infections, especially
when immunity is affected. Sometimes they can
spread intracranial leading to meningitis and
inflammation of the internal carotid artery or
cavernous sinus with consecutive thrombosis.4, 5
Another serious central nervous system infection
produced by these bacteria is the brain abscess,
characterized by the clinical triad: headache,
fever and focal neurological deficit, which may be
associated with other symptoms too (Fig. 1).
Intracranial abscess (Fig. 2) is a life-threatening
medical problem despite the progress registered
in its diagnosis and therapy.
The etiology of this infection remains unknown
in 10-40% cases, but many authors consider
the streptococci of Anginosus group the most
commonly isolated bacteria.6 Thereby, besides
making a brief description of S. anginosus
group, the aim of the present paper has been to
underline the role of these bacteria in producing
brain abscess. For this, important evidence of
S. anginosus group involvement in pathogenesis
of brain abscess has been extracted from the
publications indexed in PubMed/Medline. Only
scientific papers written in English and English
abstracts of articles written in other languages
have been selected, papers published in the last
5 years, from January 2011 to November 2015,
using all the combinations between the key words
brain or cerebral abscess and: S. anginosus,
154
Figure 2. Classification of the intracranial
abscesses
S. constellatus, S. intermedius or S. milleri.
The Anginosus streptococci may produce
cerebral abscess by contiguous spread from
a focal infection, such as: dental infections,
sinusitis, mastoiditis, otitis media.7, 8 The frontal
lobe is the main location of the brain abscess in
most patients9, but the temporal lobe is more
affected in case of otitis media complications.10
Pansinusitis may lead also to subperiosteal scalp
abscess, epidural abscess and other intracranial
abscess.11 However, some brain abscesses
develop as posttraumatic complications, including
neurosurgery and other cranial trauma followed
by wound infection and cerebritis. Another
possibility of bacterial dissemination is the
haematogenic spread at distance from the oral
cavity, respiratory or gastrointestinal tract. These
streptococci, like other microorganisms belonging
to the normal oropharyngeal flora, may produce
bacteremia also after common tooth brushing or
dental procedures. As opposed to the contiguous
dissemination which usually leads to solitary
abscess, the bacteraemia frequently generates
multiple abscesses, produced in different internal
organs.
Many papers have shown that the Anginosus
streptococci as the most common microorganisms
involved in brain abscess pathogenesis, followed
by the anaerobic bacteria. Thus, a consecutive case
series study from Pakistan indicated that S. milleri
was the most frequent etiological agent (20.7%)
of the brain abscess cases investigated, closely
followed by the anaerobic isolates (15.1%).9
Each of the 3 species may be the single etiological
agent of the brain abscess, but usually they are
isolated in association with other microorganisms,
especially with the strictly anaerobic bacteria.
The S. anginosus group causes infections mainly
in an immunocompromised host, but there are
many articles describing life-threatening infections
in previously healthy subjects too. Sometimes
STOMA.EDUJ (2015) 2 (2)