[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/) › Brucella

[Microbiology](https://durgical.com/en/microbiology/) · [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

# Brucella

- Bacterium
- Gram-negative
- For completeness

Livestock bacteria that reach people through unpasteurized milk or cheese or contact with animals: a fever that comes and goes.

Updated 2026-11-01

Also called: Brucella melitensis, Brucella abortus, Brucella suis, Brucella canis

## Key points

- Fresh cheese or raw milk, or work with livestock, plus undulant fever: brucellosis.
- Intracellular in macrophages: hepatosplenomegaly and bone marrow involvement.
- Typical bone and joint complication: sacroiliitis and spondylitis.
- Combination treatment: doxycycline plus rifampicin or an aminoglycoside.
- A common laboratory-acquired infection: warn the lab.

## At a glance

**Gram**
Gram-negative

**Shape**
Small coccobacillus

**Oxygen**
Aerobic

**Family**
Brucellaceae

**Stain**
Gram: small red coccobacilli

## Morphology

- Small, non-motile, non-encapsulated Gram-negative coccobacillus
- Facultative intracellular: lives in macrophages
- Slow-growing; a hazard for laboratory staff

## Transmission

- Unpasteurized milk and fresh cheese, undercooked meat
- Contact with blood, placentas, aborted fetuses and animal secretions (farmers, slaughterhouse workers, vets)
- Inhalation in the laboratory
- Person-to-person spread is extremely rare

**Reservoir:** Goats and sheep (B. melitensis, the most common in humans), cattle (B. abortus), pigs (B. suis) and dogs (B. canis)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Survives and multiplies inside macrophages
- Spreads through the reticuloendothelial system: liver, spleen, bone marrow and lymph nodes
- Low-toxicity lipopolysaccharide that favors chronic infection
- In animals it causes abortion (affinity for the placenta)

## Diseases it causes

- Brucellosis (undulant fever, Malta fever) [Brucellosis →](https://durgical.com/en/conditions/brucellosis/)

## Clinical picture

- Fever that rises and falls, heavy sweating, fatigue, headache and joint pain
- Hepatosplenomegaly and enlarged nodes
- Complications: sacroiliitis and spondylitis, orchitis, endocarditis (the main cause of death)
- Untreated it can become chronic

## Diagnosis

- Prolonged blood or bone marrow culture; warn the lab because of the infection risk
- Serology: agglutination (Rose Bengal, tube agglutination)
- PCR

## Treatment

Combination antibiotics to prevent relapse: doxycycline with rifampicin, or doxycycline with an aminoglycoside (streptomycin or gentamicin). Young children and pregnant women receive other combinations, such as trimethoprim-sulfamethoxazole with rifampicin.

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

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Rifampicin](https://durgical.com/en/pharmacology/rifampicin/)
- [Gentamicin](https://durgical.com/en/pharmacology/gentamicin/)
- [Streptomycin](https://durgical.com/en/pharmacology/streptomycin/)

## Prevention

- Pasteurization of milk and dairy products
- Vaccination and brucellosis control in livestock
- Gloves, goggles and protective clothing for people handling animals or birth products
- Strict laboratory precautions

## In Colombia

In Colombia bovine brucellosis from B. abortus has an official control and cattle vaccination program; human cases are seen mainly in rural workers and from drinking unpasteurized milk or eating fresh cheese.

## Memory aid

"Brucella arrives in the cheese and keeps coming back": the fever rolls like a roller coaster until two antibiotics arrive together.

## Test yourself

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

## What are the most common ways to catch brucellosis?

Drinking unpasteurized milk or eating fresh cheese, and contact with infected animals or their birth products.

## Which Brucella species causes most human disease worldwide, and which animals carry it?

Brucella melitensis, from goats and sheep.

## Which bone and joint complication is typical of brucellosis?

Sacroiliitis and spondylitis.

## Why is brucellosis treated with two antibiotics?

It is intracellular and single-drug treatment is linked to more relapses.

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

## Related

- [Francisella tularensis](https://durgical.com/en/microbiology/francisella-tularensis/)
- [Bartonella](https://durgical.com/en/microbiology/bartonella/)

## Related conditions

- [Brucellosis](https://durgical.com/en/conditions/brucellosis/)

## 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: Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

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

Sources: [Brucellosis](https://www.who.int/news-room/fact-sheets/detail/brucellosis) (WHO, 2020); [About Brucellosis](https://www.cdc.gov/brucellosis/about/index.html) (CDC, 2026).

## **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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