[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/) › Capnocytophaga canimorsus

# Capnocytophaga canimorsus

- Bacterium

## Gram-negative?

Thin wall with an outer membrane: stains pink.

- Exam priority: medium

A bacterium from the mouths of dogs and cats; after a bite it can cause rapid, severe sepsis, mostly in people without a spleen.

Updated Nov 13, 2026

Also called: dog-bite sepsis bacterium

## Quick facts

**Type**
Bacterium · [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

**Gram / shape**
Gram-negative · Thin

**Spread**
Dog bite · Not spread from person to person

**Causes**
Fulminant sepsis with septic shock · Meningitis

**Treatment**
A beta-lactam with a beta-lactamase inhibitor

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

- Dog bite + asplenia (or alcohol use) + fulminant sepsis with purpura: Capnocytophaga canimorsus.
- Thin, spindle-shaped Gram-negative rod that needs CO2 and grows slowly.
- Treat with a beta-lactam/beta-lactamase inhibitor or a carbapenem.
- Asplenic patients get antibiotic prophylaxis after a dog bite.

## At a glance

**Gram**
Gram-negative

**Shape**
Thin, long, spindle-shaped rods

**Oxygen**
Capnophilic facultative anaerobe (needs 5–10% CO2)

**Family**
Flavobacteriaceae

**Size**
Slow-growing; colonies appear after several days

## Morphology

- Thin, tapered Gram-negative rods that can form filaments
- No flagella; moves on surfaces by gliding
- Grows slowly and only with added CO2
- May be seen inside neutrophils on a peripheral blood smear in fulminant sepsis

## Transmission

- Dog bite, by far the most common route
- Scratches or animal saliva on broken skin; cats less often
- Not spread from person to person

**Reservoir:** Mouths of healthy dogs and cats

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Resists complement killing and phagocytosis
- Its lipopolysaccharide triggers little innate alarm, so bacteria multiply silently at first
- Without a spleen the blood cannot clear it, leading to overwhelming bacteraemia and disseminated intravascular coagulation

## Diseases it causes

- Fulminant sepsis with septic shock, purpura and disseminated intravascular coagulation [Sepsis and septic shock →](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- Meningitis [Bacterial meningitis →](https://durgical.com/en/conditions/bacterial-meningitis/)
- Infective endocarditis [Infective endocarditis →](https://durgical.com/en/conditions/infective-endocarditis/)
- Local infection of the bite wound [Mammalian bites (dog, cat, human) →](https://durgical.com/en/conditions/mammalian-bites/)

## Clinical picture

- Fever, vomiting, diarrhoea, headache or confusion within days to two weeks after a bite
- Petechiae that progress to purpura fulminans and gangrene of fingers and toes
- Acute kidney injury and shock; the bite itself may look trivial
- Highest risk: asplenia, alcohol use disorder, cancer and immunosuppressive drugs

## Diagnosis

- Tell the laboratory about the dog bite and the asplenia
- Blood cultures may take days to a week to become positive
- MALDI-TOF mass spectrometry or 16S rRNA sequencing identifies the isolate
- Broad-range PCR of blood or cerebrospinal fluid when cultures stay negative

## Treatment

A beta-lactam with a beta-lactamase inhibitor (ampicillin-sulbactam, amoxicillin-clavulanic acid) or a carbapenem, with third-generation cephalosporins as another option, plus intensive sepsis care. Some strains make beta-lactamase, so penicillin alone is not reliable.

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

In Pharmacology:

- [Ampicillin + sulbactam](https://durgical.com/en/pharmacology/ampicillin-sulbactam/)
- [Amoxicillin + clavulanic acid](https://durgical.com/en/pharmacology/amoxicillin-clavulanic-acid/)
- [Meropenem](https://durgical.com/en/pharmacology/meropenem/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Prevention

- Avoid bites, especially people without a spleen or with weakened immunity
- Wash any bite promptly with soap and water and seek care the same day
- Antibiotic prophylaxis with a beta-lactam/beta-lactamase inhibitor after a dog bite in asplenic people

## Memory aid

Its name says it: «canis morsus», the dog's bite; and «capno», the CO2 it craves. A small bite, a missing spleen and a huge sepsis.

## Test yourself

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

## Which underlying condition most strongly predisposes to fulminant Capnocytophaga canimorsus sepsis?

Asplenia (surgical or functional); alcohol use disorder and immunosuppression also raise the risk.

## Why may blood cultures be negative at first in Capnocytophaga sepsis?

The organism grows slowly and needs CO2; cultures can take days to a week to turn positive.

## Which antibiotic classes are used for Capnocytophaga canimorsus infection?

Beta-lactam/beta-lactamase inhibitor combinations or carbapenems; third-generation cephalosporins are an option.

## What skin sign suggests disseminated intravascular coagulation in this infection?

Purpura fulminans, which can progress to gangrene of the fingers and toes.

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

## 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

- [Pasteurella multocida](https://durgical.com/en/microbiology/pasteurella-multocida/)
- [Neisseria meningitidis](https://durgical.com/en/microbiology/neisseria-meningitidis/)
- [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/)
- [Rat-bite fever agents](https://durgical.com/en/microbiology/rat-bite-fever-agents/)

## Related conditions 4

- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/)
- [Infective endocarditis](https://durgical.com/en/conditions/infective-endocarditis/)
- [Mammalian bites (dog, cat, human)](https://durgical.com/en/conditions/mammalian-bites/)

[← Back to the group: Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

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

Sources: [About Capnocytophaga | Capnocytophaga | CDC](https://www.cdc.gov/capnocytophaga/about/index.html) (CDC, 2024); [The Great pretender: the first case of septic shock due to Capnocytophaga canimorsus in Sardinia. A Case report and review of the literature](https://pmc.ncbi.nlm.nih.gov/articles/PMC9703562/) (Journal of Public Health Research, 2022).

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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/capnocytophaga-canimorsus/