Pasteurella multocida is a bacterial microorganism primarily found in cats and dogs. Human disease, most commonly in the form of localized skin and soft tissue infection, occurs after close contact with animal hosts. Respiratory tract infections and bacteremia, particularly in immunocompromised individuals, may also occur. The diagnosis mandates a thorough clinical workup and isolation of the organism from adequate patients samples through microbiological methods.
Pasteurella multocida belongs to the normal microbial flora of the oral cavity of various animals, but is most abundant in cats and dogs, as studies estimate that up to 90% of cats and 50% of dogs harbor this pathogen in their mouths [1] [2]. Hence, this gram-negative anaerobic coccobacillus is principally encountered in general practice as a causative agent of cellulitis and soft-tissue infections developing as a result of close animal contact (a scratch or a bite) [1] [2] [3] [4]. Signs and symptoms - erythema, hyperemia, and discharge (often purulent) from the wound being typical findings, appear shortly after contact [4]. Proximal lymphadenitis is a frequent finding, while fever is reported in about 20% of cases [5] [6]. Main complications include the formation of abscesses and dissemination of the infection into the skeletal system (septic arthritis and osteomyelitis) [4] [6]. In addition to skin infections, Pasteurella multocida is also able to colonize the human respiratory tract, presumably after being in contact with carrier animals as well [4] [6]. Several reports have described the wide range of respiratory infections (from rhinosinusitis to pneumonia and abscess formation) that are seen in elderly patients suffering from chronic lung disorders or immunosuppression [3] [4] [6]. Furthermore, bacteremia and systemic infections may ensue as a complication of pneumonia and respiratory spread, particularly in patients with hepatic disease (cirrhosis), diabetes mellitus, chronic kidney disease and malignant diseases [3] [6]. Rare reports have documented endocarditis, central nervous system (CNS) infection, and intraabdominal infections by P. multocida [5].
The diagnosis of P. multocida infection should be made early on, as this bacterial pathogen is highly susceptible to antimicrobial therapy, but also because more severe forms may be life-threatening [5] [6] [7]. One of the most important parts of the workup is a thoroughly obtained patient history that will confirm recent or previous close animal contact [7]. Additionally, physicians must inquire about the presence of underlying diseases and comorbidities that could serve as risk factors for respiratory and systemic infections by P. multocida, whereas a complete physical examination is also important in identifying the site of infection. Once a presumptive diagnosis of a bacterial etiology is made, microbiological studies are necessary to determine the exact pathogen. Depending on the site, appropriate patients samples (sputum, exudate from the skin, synovial fluid, or blood) should be obtained. Cultivation of P. multocida on standard media is a convenient method for its detection, but it is frequently masked by other structurally similar pathogens that could be present in nonsterile specimens (for example, haemophilus influenzae and francisella tularensis, the causative agents of whooping cough and tularemia, respectively) [2] [5] [6] [7]. Furthermore, skin and soft-tissue infections are often polymicrobial [6]. Still, the presence of large buttery colonies on blood agars consisting of gram-negative coccobacilli, developing after only one night of incubation, should be sufficient to make the diagnosis [6]. Molecular methods, such as polymerase chain reaction (PCR), can be used for more detailed analysis of P. multocida [2].