Pasteurella multocida bacteremia in a patient with septic arthritis

Pasteurella multocida is a common commensal microorganism found in the nasopharynx of domestic and wild animals. Humans acquire P multocida infection primarily through contact with animals or their mucous secretions. P multocida is infrequently encountered in clinical settings, and it is considered as a zoonotic pathogen. In this study, we present an interesting case of septic arthritis and bacteremia caused by P multocida in a 62-year-old patient. The patient was treated with surgical procedures and antibiotic therapy, which made significant improvement. This case study highlights the importance of P multocida in causing zoonotic infection in humans.


Introduction
The members of the genus Pasteurella belonging to the family Pasteurellaceae are small, nonmotile, non-sporeforming, gram-negative microorganisms [1] .While being common commensals found in the nasopharynx of domestic and wild animals, Pasteurella can cause a variety of diseases such as hemorrhagic septicemia in cattle, atrophic rhinitis in pigs, and fowl cholera in birds [ 2 , 3 ].Pasteurellosis is used as a bacterial infection caused by Pasteurella .There are at least 30 different Pasteurella species ( https://lpsn.dsmz.de/genus/pasteurella), and Pasteurella multocida is the most common cause of human pasteurellosis because of its association with the pharyngeal flora of domestic pets [4] .P multocida is a zoonotic agent, and its transmission to humans often occurs through a bite or scratch from cats and dogs or contact with their mucous secretions [5] .However, unusual cases of vertical transmission from infected mother to neonate were also reported [6] .Every year approximately 20%-50% of 1-2 million people in the United States, who are bitten or scratched by dogs and cats, are infected by P multocida [7] .While this bacterium is often known to be associated with skin and soft tissue infections, P multocida also causes a wide range of infectious diseases in humans, includ-ing bacteremia, urinary tract infections, meningitis, endocarditis, pneumonia, brain abscess, conjunctivitis and epiglottitis, but the number of reported cases are small [ 1 , 8 ].Breen and colleagues had seen only 23 patients diagnosed with P multocida infection in a major teaching hospital laboratory over a 10-year period in Australia [9] .The majority of them (73.9%, 17 of 23) had wound infections following animal bites, 3 cases had respiratory infections, and there were one case of neonatal meningitis and associated maternal vaginal carriage of P multocida [9] .In this study, we present an interesting case of an isolated P multocida in blood, synovial fluid, synovial tissue and prosthesis from a patient who had symptoms of right knee septic arthritis.

Case presentation
A 62-year-old patient with a history of cirrhosis with esophageal varices, gastroesophageal reflux disease, hyperlipidemia and right knee arthroplasty (5 years ago) presented to the emergency room with acute onset of right knee pain.The patient stated that the swollen knee occurred over a week, and the patient was unable to bear weight on the right knee due to pain.Generalized weakness and low-grade fever developed over the last 2 days.Upon admission, the patient was febrile (38.3°C), but vitally stable.Physical examination revealed that the joint was warm to touch.Large joint effusion and decreased range of motion of the right knee were also noted on the physical examination.The X-ray showed the right total knee arthroplasty in a satisfactory alignment, and no osseous lesions were found ( Fig. 1 ).Laboratory studies conducted at the time of admission revealed an elevated leukocytes in blood; the patient's white blood cell count was 14,000 per microliter with a neutrophilic predominance of 87%.Synovial fluid aspirate from the right knee had 115,000 white blood cells per microliter and neutrophils accounted for 86%.The patient was diagnosed with prosthetic joint infectious arthritis and was started empirically on ceftriaxone (2 g intravenously once) and vancomycin (1.5 g intravenously once).The next day, the patient underwent surgical debridement and washout procedures with a polyethylene liner exchange.After the surgery, the patient was placed on cefepime (2 g intravenously every 12 hours) and vancomycin (1.5 g intravenously every 12 hours) for 3 days.Synovial fluid, synovial tissue, blood and polyethylene liner were submitted to our clinical microbiology laboratory for bacterial culture.After 24 hours of incubation at 35°C in 5% CO 2 , there were grayish and nonhemolytic colonies on the nonselective blood and chocolate agar plates, which were planted from all submitted different specimen types.However, no growth was seen on the selective Columbia CNA and MacConkey agar plates.Small gram-negative coccobacilli were observed on the microscopic examination of a gram-stained smear ( Fig. 2 ).The bacterial isolate was finally identified as P multocida by the MALDI-TOF system.Since its vancomycin resistance is common [8] , vancomycin was discontinued, and the patient continued with cefepime (2 g intravenously every 12 hours) for additional 3 days.The patient was eventually discharged and did well on the one-month follow-up visit.

Discussion
P multocida was first discovered in 1878 and later named when this bacterium was found to be responsible for fowl disease in 1880 [2] .Since then, P multocida has been commonly found in domestic pets such as cats and dogs, but it is infrequently encountered in humans.P multocida infections in clinical settings often involve softtissue sites after animal bites or scratches.However, it can cause invasive diseases in immunocompromised patients or patients with chronic diseases [ 1 , 8 ].Raffi and colleagues reported 13 cases of bacteremia caused by P multocida in a French general hospital during a 12-year period.The mortality rate was 31% and the majority (77%) of the patients had cirrhosis [10] .It is interesting that we had a rare case of P multocida bacteremia and septic arthritis in a patient with cirrhosis who had a unilateral total knee arthroplasty 5 years ago.Infection is one of serious complications of total joint arthroplasty [11] .While P multocida is an uncommon cause in prosthetic joint infections, other microorganisms such as Staphylococcus aureus , coagulase-negative staphylococci and Streptococcus species are widely responsible [12] .
A vast majority of P multocida infection in humans is directly associated with a bite and/or scratch from dogs or cats.In the study, our patient lived with a dog and denied any bite or scratch from the dog.However, P multocida infection occasionally has been reported after exposure to cats or dogs in the absence of injury.Christenson et al. presented a case of fulminant P multocida sepsis in a renal transplant patient due to the cat's licking on the venous stasis ulcers on the patient's legs [13] .In 23 cases of P multocida meningitis in infants, 6 had known exposure without physical injury to dogs only, 4 to cats only, and 3 to both [14] .Honnorat and colleges retrospectively reviewed and identified 6 P multocida infected patients among 4686 cases of prosthetic joint infection over 20 years from 1993 to 2013 in southern France [15] .Among these, 2 cases had cat scratches, dog licking on surgical wound in few days before the beginning of symptoms was found in 2 cases, and an exposure with cats or dogs in 2 cases [15] .The finding in our patient was in line with these reports that a close contact with dogs and/or cats can pose a risk for P multocida infection.Taken together, our case study underscores the important role of a zoonotic pathogen P multocida in causing infectious diseases in humans.

Fig. 1 .
Fig. 1.The preoperative radiograph showed the right total knee replacement with the prosthetic components.

Fig. 2 .
Fig.2.Grayish and non-hemolytic colonies of Pasteurella multocida were observed on sheep blood agar, and microscopic examination of a gram-stained smear revealed small gramnegative coccobacilli at 1000 x magnification.