A 35 year old healthy man presented with a puncture wound of the left hand. He was bit by his neighbor’s dog. Fluid expressed from the wound was sent to the microbiology laboratory with the following gram stain and colony morphology.
Bacterial colonies, as shown above, grew on sheep blood and chocolate agars. No growth was present on CNA or MacConkey agars which in combination with the gram stain indicated a type of fastidious gram negative bacteria. Additionally, the bacterial colonies were oxidase positive, catalase positive and indole positive. These findings were consistent with Pasteurella species and confirmed to be P. multocida by mass spectrometry.
Pasteurella species are nonmotile, gram-negative, facultative anaerobic coccobacilli or rods. P. multocida is the most common species involved in human disease. P. multocida is part of the normal oropharyngeal flora in multiple animals including cats, dogs, cattle, horses, rodents and other animals. This bacteria has been reported in up to 70-90% cats and 40-60% of dogs. Humans who have frequent exposure to animals may also harbor P. multocida as part of their normal flora.
Pasteurella are opportunistic pathogens that require mechanical disruption of host barriers. The vast majority of P. multicida related diseases are wound infections and/or cellulitis as a result of a cat bite or scratch. Transmission of Pasteurella also occurs in partially healing wound or regions of poor skin integrity that are licked by a cat or dog. Pasteurella infections may be complicated by septic arthritis and osteomyelitis if wounds are deep and inoculate the underlying soft tissue. Patients who are immunocompromised may develop bacteremia with more widespread infections. The majority of Pasteurella species are susceptible to penicillin, cephalosporins and tetracycline. Our laboratory does not report antibiotic sensitivities for P. multocida for a few reasons: Pasteurella is rarely resistant to penicillin, and bite wounds are generally mixed infections.
-Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.