From the Center for Disease Control and Prevention (CDC)
Pasteurellosis is a bacterial disease associated with animal bites and scratches. Pasteurella is a normal bacterium that lives in the mouths of healthy dogs. The bacteria do not typically make dogs sick; however, dogs can develop abscesses or skin infections in places where they were scratched or bitten by another animal.
Pasteurella is found in 50% of patients with infected dog bite wounds. Pasteurella can cause painful wound and skin infections. In more severe cases, it can cause widespread infection and might even affect the nervous system.
Pasteurella multocida is a small, gram-negative, nonmotile, non–spore-forming coccobacillus with bipolar staining features. The bacteria typically appear as single bacilli on Gram stain; however, pairs and short chains can also be seen. P multocida often exists as a commensal in the upper respiratory tracts of many livestock, poultry, and domestic pet species, especially cats and dogs. In fact, Pasteurella species are some of the most prevalent commensal bacteria present in domestic and wild animals worldwide. P multocida infection in humans is often associated with an animal bite, scratch, or lick, but infection without epidemiologic evidence of animal contact may occur. See the image below.
Wound infections associated with animal bites usually have a polymicrobial etiology, mandating the empiric use of broad-spectrum antimicrobials targeted at both aerobic and anaerobic gram-negative bacteria. Nevertheless, Pasteurella species are commonly isolated pathogens in most animal bites, especially in dog- and cat-related injuries. These injuries can be aggressive, with skin manifestations typically appearing within 24 hours following a bite. These wounds can exhibit a rapidly progressive soft-tissue inflammation that may resemble group A β-hemolytic Streptococcus pyogenes infections.
Deeper soft tissue can also be affected, manifesting as tenosynovitis, septic arthritis, and osteomyelitis. More-severe disseminating infections may also develop, including endocarditis or meningitis, the latter mimicking Haemophilus influenzae or Neisseria meningitides infections in young children. Fortunately, Pasteurella species are fairly sensitive organisms and can be treated with a penicillin-based regimen.