[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/) › Pasteurella multocida [Microbiology](https://durgical.com/en/microbiology/) · [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/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 ## Key points - Cat or dog bite with cellulitis in under 24 hours: Pasteurella multocida. - Classic treatment and prophylaxis: amoxicillin-clavulanate. - Dicloxacillin, cephalexin and clindamycin alone cover it poorly. - Cat bites to the hand are complicated by tenosynovitis and osteomyelitis. ## 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 →](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - Osteomyelitis, septic arthritis or tenosynovitis after deep bites, above all of the hand [Osteomyelitis →](https://durgical.com/en/conditions/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: - [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/) - [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/) ## 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 ## Memory aid "Pasteurella passes fast": the morning bite is already red and hot by the afternoon; if it takes days, think of Staphylococcus too. ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/pasteurella-multocida/) ## Related - [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/) - [Bartonella](https://durgical.com/en/microbiology/bartonella/) - [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/) ## Related conditions - [Cellulitis of the leg](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/) ## 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 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: [Pasteurellosis: characteristics, diagnosis and management](https://www.gov.uk/pasteurellosis) (UK Health Security Agency (GOV.UK), 2025); Jawetz, Melnick & Adelberg's Medical Microbiology, 26th ed., chapter 19: Yersinia and Pasteurella (McGraw-Hill, 2013). ## **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. --- Source: https://durgical.com/en/microbiology/pasteurella-multocida/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/pasteurella-multocida/