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Streptococcus intermedius
Scientific classification
Domain:	Bacteria
Phylum:	Bacillota
Class:	Bacilli
Order:	Lactobacillales
Family:	Streptococcaceae
Genus:	Streptococcus
Species:	S. intermedius
Binomial name
	Streptococcus intermedius; Prévot 1925 (Approved Lists 1980)

Streptococcus intermedius is an aerotolerant anaerobic commensal bacterium and a member of the Streptococcus anginosus group. The S. anginosus group, occasionally termed “Streptococcus milleri group” (SMG) display hemolytic and serologic diversity, yet share core physiological traits. Though the three members of the SMG are phenotypically diverse, one common trait they share is the mechanism of producing the metabolite diacetyl, which contributes to generating a signature caramel odor.^[1]^[2] Despite being commensal organisms, members of the S. anginosus group display wide pathogenic potential. S. intermedius has been isolated from patients with periodontitis and fatal purulent infections, especially brain and liver abscesses.^[3]^[4]

Researchers identified the isolates to species that led to 118 cases of infection due to SMG using 16S rRNA gene sequence and biochemical tests. This study, done in 2002 used identification of clinical isolates recovered and stored at the Microbiology Laboratory, Veterans Affairs Medical Center, Houston during 1989–1999. It has been difficult to reliably identify the differences between the members of SMG on a species level. However, some additional approaches to isolate this strain include analyzing blood agar plates, real-time PCR, and mass spectrometry.^[5]^[6] In summary, different strains were characterized as belonging to the Streptococcus milleri group. S. intermedius was found to be the least commonly isolated member of the SMG (14 of 122 isolates). The majority of which (12 or 86%) were recovered from an abscess or from a site associated with an abscess (blood abscess). Therefore 86% of isolates of this species were attributed to an abscess. The limited study and clinical data on how to treat symptoms of brain and liver abscess include abscess drainage, surgery, and taking preventative antibiotics that include a combination of ceftriaxone and metronidazole.^[7]^[8] Data from the study support observations that members of the SMG have a tendency to cause abscesses, however they do not cause them with equal frequency. S. intermedius were more likely to cause deep-seated abscess and was found as a solitary isolate in specimens obtained.^[3]

References

^ Brogan, O.; Malone, J.; Fox, C.; Whyte, A. S. (1997-04-01). "Lancefield grouping and smell of caramel for presumptive identification and assessment of pathogenicity in the Streptococcus milleri group". Journal of Clinical Pathology. 50 (4): 332–335. doi:10.1136/jcp.50.4.332. ISSN 0021-9746. PMC 499886. PMID 9215152.
^ Chew, T A; Smith, J M (1992–2011). "Detection of diacetyl (caramel odor) in presumptive identification of the "Streptococcus milleri" group". Journal of Clinical Microbiology. 30 (11): 3028–3029. doi:10.1128/jcm.30.11.3028-3029.1992. ISSN 0095-1137. PMC 270577. PMID 1452678.
^ ^a ^b Claridge, J. E., III, S. Attorri, D. M. Musher, J. Hebert, and S. Dunbar. 2001. Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus (“Streptococcus milleri group”) are of different clinical importance and are not equally associated with abscess. Clin. Infect. Dis. 32:1511–1515.
^ Whiley, R. A., D. Beighton, T. G. Winstanley, H. Y. Fraser, and J. M. Hardie. 1992. Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus (the Streptococcus milleri group): association with different body sites and clinical infections. J. Clin. Microbiol. 30:243–244.
^ Takao, Ayuko; Nagamune, Hideaki; Maeda, Nobuko (2004). "Identification of the anginosus group within the genus Streptococcus using polymerase chain reaction". FEMS Microbiology Letters. 233 (1): 83–89. doi:10.1016/j.femsle.2004.01.042. PMID 15043873.
^ Friedrichs, C.; Rodloff, A. C.; Chhatwal, G. S.; Schellenberger, W.; Eschrich, K. (2007–2008). "Rapid Identification of Viridans Streptococci by Mass Spectrometric Discrimination". Journal of Clinical Microbiology. 45 (8): 2392–2397. doi:10.1128/JCM.00556-07. ISSN 0095-1137. PMC 1951256. PMID 17553974.
^ De Louvois, E.M. Brown, R. Bayston, P.D. Lees, I.K. Pople, J. (2000-01-01). "The rational use of antibiotics in the treatment of brain abscess". British Journal of Neurosurgery. 14 (6): 525–530. doi:10.1080/02688690020005527. ISSN 0268-8697. PMID 11272029. S2CID 219187914.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Yakut, Nurhayat; Kadayifci, Eda Kepenekli; Karaaslan, Ayse; Atici, Serkan; Akkoc, Gulsen; Ocal Demir, Sevliya; Dagcinar, Adnan; Akbulut, Fatih; Soysal, Ahmet; Bakır, Mustafa (2015-12-23). "Braın abscess due to Streptococcus intermedius secondary to mastoiditis in a child". SpringerPlus. 4 (1): 809. doi:10.1186/s40064-015-1608-0. ISSN 2193-1801. PMC 4689728. PMID 26722629.