Pasteurella multocida

Morphology

• Gram-negative, nonmotile.
•  Strains belonging to the species are currently classified into five serogroups (A, B, D, E, F) based on capsular composition and 16 somatic serovars (1-16).

Epidemiology and pathogenesis

• Cat and dog bites frequently become infected
• P. multocida is the most commonly cultured bacterium from infected bite wounds.
•  Apart from bites, scratches and licks, close contact has also been sufficient for infection.
• Bacteria usually enter through skin wounds, but inhalation of secretion droplets from the upper respiratory tract is another possible source.

Disease in humans 

• Infection typically produces cellulitis and/or abscesses at the site of the bite or scratch
• Usually 3 to 6 hours after inoculation
• Occasionally, the local infection can progress to necrotising fascitis, septic arthritis and osteomyelitis.
• Respiratory infection, pneumonia and bronchopneumonia also are common, mostly in patients with a pre-existing lung disease.
• Less frequently, a disseminating infection may produce septicaemia, which may lead to septic shock, meningitis, endocarditis, peritonitis, arthritis and other serious consequences. 
• Pasteurella peritonitis through a dialysis catheter after contact with a cat has been reported . 
• Severe infections are usually seen in children, pregnant women, patients on chronic immunosupressive therapy, and immunocompromised persons. .

Diagnosis 

• Diagnosis is made on the basis of bacterial culture from infected tissues or secretions.
•  Pasteurella grows readily on chocolate and sheep-blood agar media, but fails to grow on MacConkey agar, the usual medium for Gram-negative bacteria.
• Strains are usually catalase-, oxidase-, indole- and sucrose-positive. 

Treatment and prevention 

• Penicillins and potentiated beta-lactamics (amoxicillin-clavunalate potassium) are first line antibiotics for the treatment of Pasteurella infections. 
• Quinolones, cephalosporins and modern macrolids are also indicated.