Microbiology · Other clinically important bacteria
Pasteurella multocida !
- Bacterium
- Gram-negative
- For completeness
A bacterium from the mouths of dogs and cats that infects bites and scratches: the skin turns red, swollen and painful within hours.
Updated 2026-11-01
At a glance
- Gram
- Gram-negative
- Shape
- Coccobacillus
- Oxygen
- Aerobe or facultative anaerobe
- Family
- Pasteurellaceae
- Stain
- Bipolar ("safety pin") staining on smears
Morphology
- Small, non-motile Gram-negative coccobacillus
- Stains more darkly at both ends (bipolar)
- Oxidase and catalase positive; grows on blood agar
Transmission
- Cat or dog bite or scratch (cats more often, because their thin teeth go deep)
- An animal licking broken skin
- Rarely by the respiratory route in people with lung disease
Reservoir: Upper airways and mouths of cats, dogs and other domestic and wild animals, which stay healthy
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Capsule that resists phagocytosis
- Very fast local inflammation in the inoculated tissue
- A deep bite carries it into tendons, joints and bone
Diseases it causes
- Cellulitis after a bite or scratch Cellulitis of the leg →
- Osteomyelitis, septic arthritis or tenosynovitis after deep bites, above all of the hand Osteomyelitis →
Clinical picture
- Redness, swelling and intense pain within 24 hours of the bite
- Wound discharge and regional lymphadenopathy
- In people with cirrhosis or immunosuppression it may cause bacteraemia or meningitis
Diagnosis
- History of a cat or dog bite or scratch
- Gram stain and culture of wound discharge
- X-ray if bone or joint involvement is suspected
Treatment
Wound cleaning and debridement, plus beta-lactams: amoxicillin-clavulanate is the usual choice because it also covers other bacteria from the animal's mouth. Penicillin is active; alternatives are doxycycline or fluoroquinolones. Antistaphylococcal penicillins, first-generation cephalosporins and clindamycin cover Pasteurella poorly.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Wash every bite or scratch with plenty of soap and water
- Antibiotic prophylaxis for cat bites, hand bites and deep bites
- Always assess rabies and tetanus risk
Test yourself
Think of the answer, then tap the question to see it.
Which bacterium is suspected in cellulitis that starts a few hours after a cat bite?
Pasteurella multocida.
Which antibiotic is most often used to treat or prevent bite-wound infection?
Amoxicillin-clavulanate, which covers Pasteurella and the anaerobes and staphylococci of mouth and skin.
Why do cat bites get infected more often than dog bites?
Cat teeth are thin and deep and inoculate bacteria into tendons, joints and bone.
Which other risks are always assessed after an animal bite?
Rabies and tetanus.
Related
Related conditions
← Back to the group: 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: Pasteurellosis: characteristics, diagnosis and management (UK Health Security Agency (GOV.UK), 2025); Jawetz, Melnick & Adelberg's Medical Microbiology, 26th ed., chapter 19: Yersinia and Pasteurella (McGraw-Hill, 2013).
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Representative model, for educational purposes only.