[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 agalactiae

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

# Streptococcus agalactiae

- Bacterium
- Gram-positive
- Exam priority: medium

A bacterium that lives in the gut and vagina of many pregnant women and can cause sepsis, pneumonia and meningitis in the newborn.

Updated 2026-11-01

Also called: group B streptococcus, GBS

## Key points

- The classic leading cause of newborn sepsis and meningitis.
- Bacitracin resistant, CAMP positive.
- Early onset: under 7 days; late onset: 7 to 89 days.
- Prenatal screening and intrapartum prophylaxis.

## At a glance

**Gram**
Gram-positive

**Shape**
Cocci in chains

**Oxygen**
Facultative anaerobe

**Family**
Streptococcaceae

**Stain**
Gram positive; catalase negative; beta-haemolytic

## Morphology

- Gram-positive cocci in chains
- Narrow zone of beta-haemolysis
- Bacitracin resistant; CAMP positive; hydrolyses hippurate

## Transmission

- From the mother's genital and gut tract to the baby during birth
- The source of late-onset disease is often unclear

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Polysaccharide capsule rich in sialic acid
- CAMP factor

## Diseases it causes

- Early-onset (under 7 days) and late-onset neonatal sepsis [Neonatal sepsis →](https://durgical.com/en/conditions/neonatal-sepsis/)
- Neonatal meningitis [Bacterial meningitis →](https://durgical.com/en/conditions/bacterial-meningitis/)

## Clinical picture

- Newborn with breathing difficulty, apnoea or unstable temperature
- Infections in pregnant and postpartum women and in older adults with diabetes or cancer

## Diagnosis

- Prenatal screening with a vaginal-rectal culture
- CAMP positive, bacitracin resistant, hippurate positive
- Blood and cerebrospinal fluid cultures in the newborn

## Treatment

Penicillin or ampicillin are preferred. Intrapartum antibiotic prophylaxis for colonised mothers reduces early-onset disease.

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/)

## Prevention

- Universal prenatal screening
- Antibiotic prophylaxis during labour when indicated

## Memory aid

Group B is for Babies: it rides down the birth canal and arrives with the newborn.

## Test yourself

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

## Which lab test is characteristic of group B streptococcus?

A positive CAMP test (plus bacitracin resistance).

## How is early-onset group B sepsis prevented?

With prenatal screening and intrapartum antibiotic prophylaxis for colonised mothers.

## Which three classic bacteria cause newborn sepsis and meningitis?

Group B streptococcus, Escherichia coli and Listeria monocytogenes.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/streptococcus-agalactiae/)

## Related

- [Listeria monocytogenes](https://durgical.com/en/microbiology/listeria-monocytogenes/)
- [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/)

## Related conditions

- [Neonatal sepsis](https://durgical.com/en/conditions/neonatal-sepsis/)
- [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/)

## 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.

[← 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: [About Group B Strep Disease](https://www.cdc.gov/group-b-strep/about/index.html) (CDC, 2024); [Clinical Overview of Group B Strep Disease](https://www.cdc.gov/group-b-strep/hcp/clinical-overview/index.html) (CDC, 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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