Fastidiosos

Pasteurella multocida

Gram-negative coccobacilli with bipolar staining

Identification & Growth

Identification

Oxidase-positive, catalase-positive, indole-positive, non-motile
Does not grow on MacConkey — a decisive bench clue

Growth Conditions

Blood and chocolate agar, 35–37 °C, 24 h, sweetish odour

Clinical Significance

Rapidly progressing cellulitis after dog or cat bites and scratches
Septic arthritis, tenosynovitis and, in COPD, respiratory infection

Intrinsic Resistance

Intrinsic resistance to clindamycin and vancomycin; aminoglycosides have poor in vivo activity

Bench Alerts

Amoxicillin-clavulanate is the drug of choice; cefalexin and clindamycin fail
Always ask about animal contact when the Gram stain suggests this organism

Clinical Notes

Clinical presentations

Rapidly progressive cellulitis and soft-tissue infection following dog or cat bite or scratch, with pain and inflammatory signs already within 24 h.
Septic arthritis and osteomyelitis from direct inoculation in bites near joints, especially in the hands.
Respiratory infections (sinusitis, COPD exacerbation, pneumonia) and, rarely, bacteremia and meningitis in patients with domestic animal exposure.

Specimens and collection

Culture of wound discharge and, where possible, deep material by aspiration, avoiding a superficial swab that underestimates the infection.
Blood culture in patients with systemic signs or immunosuppression, especially those with liver disease or asplenia after animal exposure.
Record the bite/scratch history and the animal involved on the request form, as it guides suspicion and interpretation of the isolate.

Epidemiology and at-risk populations

Colonizes the oropharynx of dogs and, especially, cats; most human infections follow a bite, scratch or wound-licking exposure.
Cat bites carry higher infection risk than dog bites, due to deeper inoculation from thin, sharp teeth.
Severe systemic disease (bacteremia, peritonitis) is more frequent in cirrhotic, asplenic and other immunocompromised patients.

Resistance and therapeutic implications

Amoxicillin-clavulanate is the treatment of choice for dog and cat bites, also covering the polymicrobial oral flora of the animal.
Intrinsic resistance to clindamycin and to cephalexin alone, making them unsuitable as empirical monotherapy for animal bites.
EUCAST publishes breakpoints for Pasteurella multocida; confirm susceptibility to beta-lactams and to doxycycline in case of penicillin allergy.

Bench and reporting notes

Oxidase- and catalase-positive, non-motile Gram-negative coccobacillus with a characteristic odor, growing on blood agar without significant hemolysis.
Does not grow on MacConkey agar, a useful finding to differentiate it from Enterobacterales in bite-wound culture.
Flag the relevance of the animal exposure history in the report, as it guides both interpretation of the isolate and therapy choice.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Pasteurella multocida in the lab?

Pasteurella multocida is identified through oxidase-positive, catalase-positive, indole-positive, non-motile, does not grow on macconkey — a decisive bench clue.

What are the intrinsic resistances of Pasteurella multocida?

This organism is naturally resistant to intrinsic resistance to clindamycin and vancomycin; aminoglycosides have poor in vivo activity. These drugs should not be reported as susceptible.

Where is Pasteurella multocida commonly found?

It is typically associated with rapidly progressing cellulitis after dog or cat bites and scratches, septic arthritis, tenosynovitis and, in copd, respiratory infection.

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