[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Streptococci and enterococci](https://durgical.com/en/microbiology/groups/streptococci-and-enterococci/) › Streptococcus anginosus group

# Streptococcus anginosus group

- Bacterium

## Gram-positive?

Thick peptidoglycan wall: stains purple.

- Exam priority: medium

Mouth and gut streptococci with a talent for abscesses: brain, liver, lung and neck.

Updated Nov 13, 2026

Also called: Streptococcus milleri group, S. anginosus, S. constellatus, S. intermedius

## Quick facts

**Type**
Bacterium · [Streptococci and enterococci](https://durgical.com/en/microbiology/groups/streptococci-and-enterococci/)

**Gram / shape**
Gram-positive · Cocci in chains

**Spread**
Endogenous · Spread follows a breach

**Causes**
Brain abscess · Pyogenic liver abscess

**Treatment**
Drainage is the key

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Streptococcus in an abscess (brain, liver, lung, neck): think anginosus group.
- Blood culture with S. anginosus group: search for an abscess.
- Small colonies, variable haemolysis and Lancefield antigen, caramel smell.
- Treat with drainage plus a beta-lactam; cover anaerobes in mixed abscesses.

## At a glance

**Gram**
Gram-positive

**Shape**
Cocci in chains

**Oxygen**
Facultative anaerobes; many grow best with extra CO2

**Family**
Streptococcaceae

**Size**
Small (pinpoint) colonies

## Morphology

- Gram-positive cocci in chains; catalase-negative
- Haemolysis varies: alpha, beta or none
- Lancefield antigen varies (A, C, F, G or none), so grouping does not identify them
- Cultures often have a sweet caramel-like smell

## Transmission

- Endogenous: from the mouth, throat, gut or genital tract
- Spread follows a breach: dental infection, sinusitis, bowel disease or surgery
- Not spread from person to person

**Reservoir:** Human mouth (dental plaque), oropharynx, gut and genitourinary tract

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Enzymes such as hyaluronidase and DNase break down tissue and help form pus
- S. intermedius makes intermedilysin, a toxin that targets human cells
- Synergy with anaerobes in mixed abscesses

## Diseases it causes

- Brain abscess, often from sinus or dental infection (especially S. intermedius) [Brain abscess →](https://durgical.com/en/conditions/brain-abscess/)
- Pyogenic liver abscess [Pyogenic liver abscess →](https://durgical.com/en/conditions/pyogenic-liver-abscess/)
- Empyema and lung abscess (especially S. constellatus) [Parapneumonic effusion and empyema →](https://durgical.com/en/conditions/parapneumonic-effusion-and-empyema/)
- Deep neck and peritonsillar abscess [Deep neck infection and Ludwig angina →](https://durgical.com/en/conditions/deep-neck-infection-and-ludwig-angina/)
- Intra-abdominal and pelvic abscesses (especially S. anginosus) [Intra-abdominal abscess →](https://durgical.com/en/conditions/intra-abdominal-abscess/)

## Clinical picture

- Fever with a space-occupying lesion; symptoms depend on the abscess site
- When it grows in blood, look for a hidden abscess
- Often part of a mixed infection with Fusobacterium, Prevotella or anaerobic cocci

## Diagnosis

- Culture of pus obtained by drainage or aspiration, plus blood cultures
- Imaging (CT, MRI, ultrasound) to find and drain the abscess
- MALDI-TOF mass spectrometry identifies the species; grouping antigens are unreliable
- Brain abscess cultures may be negative after antibiotics; molecular tests help

## Treatment

Drainage is the key, plus beta-lactams (penicillin, ampicillin or ceftriaxone), to which most strains are susceptible; add metronidazole when anaerobes are likely. Reduced penicillin susceptibility occurs, so test isolates; vancomycin is used for beta-lactam allergy.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/)
- [Ampicillin](https://durgical.com/en/pharmacology/ampicillin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)
- [Metronidazole](https://durgical.com/en/pharmacology/metronidazole/)
- [Vancomycin](https://durgical.com/en/pharmacology/vancomycin/)

## Prevention

- Good dental care and treatment of dental and sinus infections
- No vaccine

## Memory aid

«Milleri makes a million abscesses»: wherever this streptococcus goes, it digs a pocket of pus.

## Test yourself

Think of the answer, then tap the question to see it.

## Which group of streptococci is known for forming abscesses?

The Streptococcus anginosus group: S. anginosus, S. constellatus and S. intermedius.

## What should be done when the S. anginosus group grows in a blood culture?

Look for a hidden abscess, for example in the liver, brain, lung or abdomen.

## Why is Lancefield grouping unhelpful for this group?

Its members carry different antigens (A, C, F, G) or none at all.

## Which member is most linked to brain abscess?

Streptococcus intermedius.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/streptococcus-anginosus-group/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

## Connections

## Related 4

- [Viridans streptococci](https://durgical.com/en/microbiology/viridans-streptococci/)
- [Fusobacterium, Prevotella and Porphyromonas](https://durgical.com/en/microbiology/fusobacterium-prevotella-and-porphyromonas/)
- [Anaerobic Gram-positive cocci](https://durgical.com/en/microbiology/anaerobic-gram-positive-cocci/)
- [Streptococcus dysgalactiae](https://durgical.com/en/microbiology/streptococcus-dysgalactiae/)

## Related conditions 5

- [Brain abscess](https://durgical.com/en/conditions/brain-abscess/)
- [Pyogenic liver abscess](https://durgical.com/en/conditions/pyogenic-liver-abscess/)
- [Parapneumonic effusion and empyema](https://durgical.com/en/conditions/parapneumonic-effusion-and-empyema/)
- [Deep neck infection and Ludwig angina](https://durgical.com/en/conditions/deep-neck-infection-and-ludwig-angina/)
- [Intra-abdominal abscess](https://durgical.com/en/conditions/intra-abdominal-abscess/)

[← Back to the group: Streptococci and enterococci](https://durgical.com/en/microbiology/groups/streptococci-and-enterococci/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [The Clinical View on Streptococcus anginosus Group – Opportunistic Pathogens Coming Out of Hiding](https://pmc.ncbi.nlm.nih.gov/articles/PMC9309248/) (Frontiers in Microbiology, 2022); [Infections Caused by Group C and G Streptococcus (Streptococcus dysgalactiae subsp. equisimilis and Others): Epidemiological and Clinical Aspects](https://pmc.ncbi.nlm.nih.gov/articles/PMC11590429/) (Microbiology Spectrum (ASM), 2019); [Streptococcal Infections - Infectious Disease - MSD Manual Professional Edition](https://www.msdmanuals.com/professional/infectious-diseases/gram-positive-cocci/streptococcal-infections) (MSD Manual Professional Edition, 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/streptococcus-anginosus-group/