Pasteurella multocida

Open the mouth of most dogs or cats and you will likely find the bacterium Pasteurella multocida. This nonmotile, non–spore-forming, gram-negative coccobacillus is part of normal animal respiratory flora and, therefore, is a common cause of wound infections due to animal bites.

The isolation and description of this organism was first made by Louis Pasteur in 1880, 3 years after it was discovered in birds with fowl cholera. In 1930, Kapel and Holm identified its first true human infection, which was secondary to a cat bite. Further classification of the bacterium over the years ultimately led to the name Pasteurella multocida in 1939. Pasteurella multocida is a facultatively anaerobic organism that grows on sheep’s blood, chocolate, and Mueller-Hinton agar but has no growth on MacConkey medium. It is usually seen as a single bacillus but is sometimes seen in pairs, chains, or clusters. Just 10 minutes of direct exposure to sunlight kills the organism, but it can live in soil for up to 21 days and in water for up to 25 days.

Although P multocida can cause serious disease in a variety of animals, this review focuses on human infections. Commonly found in oral or nasal secretions of many animals, including lions, tigers, and buffalo, P multocida has been reported in as many as 90% of cats and 50% of dogs. Not surprisingly, human infections generally occur after cat or dog bites, or cat scratches or licks. No food or waterborne illness has been reported. Human-to-human transmission has been reported horizontally via contaminated blood products or from colonized humans via nasopharyngeal secretions, feces, …