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

Sophie Arbefeville, MD; Anthony Harris, BS; Steven Dittes, MD; Patricia Ferrieri, MD


Lab Med. 2016;47(3):241-245. 

In This Article

Case Report

The patient was an 80-year-old Caucasian man who arrived at the emergency department (ED) of Fairview Southdale, Minneapolis, MN, via the Emergency Medical Service (EMS) for evaluation of leg weakness. In the early morning hours, while attempting to rise from bed to use the bathroom, the patient discovered that his legs were weak and he was unable to stand. Later that morning, the patient had a similar episode of leg weakness, prompting the EMS to bring him to the ED for evaluation. The patient complained of shortness of breath, bilateral leg weakness, and right knee pain for the past 2 weeks, intermittent fever for the past week, and decreased fluids and food intake on the day of admission. His past medical history was relevant: he had undergone a right total-knee arthroplastic procedure 6 years ago; mitral and tricuspid valve repair 10 months before admission; and atrial fibrillation, for which he was taking generic warfarin sodium (Coumadin; Bristol-Myers Squibb).

On physical examination, the patient appeared to be in moderate distress and was slightly diaphoretic. His vital signs were as follows: blood pressure, 82/72 mmHg; pulse rate, 129 beats per minute; oral temperature, 39 °C; respiratory rate, 21 breaths per minute; and oxygen saturation, 97% when breathing room air. His entire lower extremities showed intact skin, as well as palpable pulses with intact motor and sensory neurologic functioning on examination. There was a well-healed midline incision on the anterior right knee, with trace effusion and no erythema or warmth. Tenderness was noted laterally along the right knee, superiorly in the suprapatellar pouch, and medially. The range of motion of the right knee and right hip was limited, passively and actively. Examination of the left leg revealed intact neurovascular status, with full range of motion and no tenderness. The lymphatic examination results were negative.

The chemistry panel results were significant for a C-reactive protein (CRP) level of 206.0 mg per L (0–8.0 mg/L); lactic acid, 4.0 mmol per L (0.4 to 2.0 mmol/L); and creatinine, 1.81 mg per dL (0.94 mg/dL from previous admission). Urinalysis results showed 30 mg per dL of protein, 2 white blood cells, 12 red blood cells, a few bacteria, mucus present, and a few amorphous crystals. The complete blood count yielded a leukocyte count of 8.6 × 10e9 per L (4.0–11.0 × 10e9/L), red blood cell count of 4.74, hemoglobin of 11.0 g per dL (13.3 to 17.7 g/dL), and platelet count of 143 × 10e9 per L (150–450 × 10e9/L). The international normalized ratio (INR) was 3.60 (0.86–1.14).

Two sets of blood culture were obtained. The patient's chest x-ray for the patient showed clear lungs with no apparent pleural effusion. X-rays of the right knee were performed, and it was reported that right total-knee arthroplasty had been performed on the patient (Image 1). The patient was treated with piperacillin/tazobactam and vancomycin and sent to the intensive care unit (ICU) for sepsis management. The Department of Orthopedics was consulted, and right knee joint aspiration was performed the following day.

Image 1.

X-Ray of the right knee of the patient, an 80-year-old Caucasian man. Previously, the patient had undergone right total-knee arthroplasty; his results revealed no obvious radiolucencies or joint effusion.

Both sets of blood cultures were flagged as having bacterial growth after 1 day of incubation. On Gram staining, we observed pleomorphic gram-negative organisms with ovoid short bacilli (coccobacilli) and short chains (Image 2A) also, small gray colonies grew on 5% sheep's blood and chocolate agars, but no growth was observed on MacConkey agar. The isolate was referred to the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) instrument for identification; the result was P. multocida.

Image 2.

Gram staining of specimens from our patient, an 80-year-old Caucasian man. A, Blood culture gram-negative coccobacilli (oil, original magnification ×1000). B, Right-knee fluid aspirate; arrows point to gram-negative coccobacilli (oil, original magnification ×1000).

The fluid aspirate from the right knee appeared purulent, and Gram staining showed moderate gram-negative coccobacilli and many polymorphonuclear leukocytes (Image 2B). The fluid was plated directly onto a blood agar plate and a chocolate agar plate, as well as into a thioglycollate broth. From the broth only, on the second day of incubation, P. multocida was also isolated. Both isolates were catalase, oxidase, indole positive, and reduced nitrate to nitrite, consistent with the identification of P. multocida.

The isolates were susceptible to ampicillin, ceftriaxone, levofloxacin, penicillin, and trimethoprim/sulfamethoxazole. In addition, pure colonies from the blood and fluid culture were processed independently for nucleic acid extraction and sequencing. The 16S rRNA gene region was amplified by polymerase chain reaction (PCR) and sequenced using an Applied Biosystems 3130 Genetic Analyzer (Life Technologies). We analyzed the forward and reverse sequences produced, using Sequencher v4.8 software (Gene Codes Corporation), and a final sequence was generated. We performed searches on the final sequences for both isolates within the GenBank database using the BLAST algorithm, and P. multocida was the best sequence match, at 100% (AY299314.1), for both isolates. The sequences were then compared against the Ribosomal Database Projects database; again, P. multocida contained the highest similarity score, at 0.986/1.000 (RDPII S000389472/GenBank: AF225205). Both databases also showed that the isolates were most closely related to P. multocida subsp. septica. Further, to determine the similarity between both isolates, their sequences were aligned to one another using the National Center for Biotechnology Information (NCBI) nucleotide BLAST function.

This alignment showed that both sequences were a 100% match.

After further investigation, we discovered that the patient owned a Pomeranian dog that nipped at his legs periodically. However, the patient did not recall having any actual infected wounds or any major skin breakdown.

The patient received a resection of his right total-knee arthroplasty and placement of an antibiotic spacer with tobramycin. His echocardiogram result was negative for vegetations. He was treated with intravenous (IV) ceftriaxone for 6 weeks. After the completion of his antibiotic course the patient underwent a revision of his right total knee arthroplasty with no complication.