Pasteurella multocida infection — apparent failure of ampicillin treatment

Pasteurella multocida is a common oropharyngeal commensal in many animals and is particularly common in cats (70 to 90% carriage) and dogs (50 to 66% carriage). Human infections are frequent and are usually associated with animal exposure. The majority are soft tissue infections that typically follow animal bites or scratches. Non-bite animal exposures leading to P. multocida infections are much less common but are associated with infections such as pneumonia, septic arthritis, osteomyelitis, endocarditis, and meningitis. Traditionally, penicillin has been regarded as the antibiotic of choice for suspected or confirmed P. multocida infections, with ampicillin being a recognized alternative. Treatment failures with erythromycin are well documented, as are rare cases of human infection with penicillin-resistant strains. To our knowledge, treatment failure with ampicillin has not been described previously. We report two cases of P. multocida infection, one demonstrating clinical failure with ampicillin, the other successful treatment with a third-generation cephalosporin.