Pasteurella multocida Bacteremia with Associated Knee Arthroplasty Infection in an 80-Year-Old Caucasian Man

Objectives: To identify the gram-negative rods grown from blood cultures and a right-knee fluid aspirate from an 80-year-old caucasian man who had undergone a total right knee arthroplastic procedure 6 years ago, and to assess the genetic similarity between the 2 isolates. Methods: We used 3 different approaches: biochemical testing, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and 16S ribosomal RNA (rRNA) gene sequencing. Results: The 3 methods identified the gram-negative rods as Pasteurella multocida; 16S rRNA gene sequencing further identified the organisms as P. multocida subsp. septica. Conclusion: A concordant identification of P. multocida was observed using biochemical testing, mass spectrometry, and 16S rRNA gene sequencing. Only 16S rRNA sequencing was able to determine the subspecies of P. multocida and to determine the genetic relatedness of the 2 isolates.