A 10 month old African American female presented to the emergency department with fever (101.9°F) and a two day history of left shoulder pain. Her mother reported guarding and refusal to move the left arm. There was no history of trauma and no other relevant past medical history. On examination, there was tenderness with gentle manipulation of left shoulder but no erythema or swelling were noted. She had full range of motion of elbow, wrist and finger joints with adequate sensation and pulses. Lab work showed a normal white blood cell count and increased ESR (52mm/hr, normal range: 0-20 mm/hr) and CRP (1.5 mg/dL, normal range: <1.00 mg/dL), suggestive of an infectious or inflammatory process. X-ray of the shoulder showed no bony abnormalities. Orthopedic surgery ordered an MRI which revealed a joint effusion concerning for septic arthritis. She underwent an aspiration with irrigation of the glenohumeral joint with drain placement and was subsequently started on clindamycin. The fluid was sent to the microbiology laboratory for Gram stain and bacterial culture. Multiple blood cultures were also collected.
The initial direct Gram stain from the fluid showed rare white blood cells and no organisms were identified. Two colonies of the organism grew on chocolate agar as small, grayish colonies after 48 hours incubation (Image 1). Upon subculture, the organism failed to grow on MacConkey agar (Image 2). Gram stain identified the isolate as gram negative bacilli, predominantly arranged in pairs (Image 3). The isolate was positive for oxidase and negative for catalase. MALDI-TOF MS identified the isolate as Kingella kingae. All blood cultures were negative.
Kingella kingae is a short, gram-negative bacilli that occur in pairs or short chains and require increased CO2 for optimum growth. K. kingae is the most common species responsible for human infections and is characterized as a fastidious gram negative rod of the HACEK group. K. kingae is a component of the normal flora in the oral cavity, throat, and upper respiratory tract of children and adults.
Bone and joint infections are the most common clinical manifestations of K. kingae infection in children and can present as bacteremia, septic arthritis, osteomyelitis and discitis. Children usually show symptoms including fever, swollen joints and decreased mobility with a recent preceding history of an upper respiratory tract infections or stomatitis with K. kingae gaining access to the bloodstream through damaged mucosa. In adults, those with poor dental hygiene, immunosuppression, or recent chemotherapy with mucositis are at risk for subacute bacterial endocarditis.
In the microbiology laboratory, K. kingae are facultative anaerobic gram negative bacilli that grow well on blood and chocolate agar plates after 48 hours. There is a small but distinct zone of beta-hemolysis on blood agar. Unlike enteric organisms, K. kingae does not grow on MacConkey agar. Biochemical tests for K. kingae show a negative catalase reaction, positive oxidase positive reaction and they are non-motile. K. kingae is negative for indole and urease reactions. Automated identification instruments and MALDI-TOF mass spectrometry are able to identify K. kingae.
Beta-lactamase testing should be performed on K. kingae isolates as production among members of the HACEK group is well known. If the isolate is beta-lactamase positive, this predicts resistance to ampicillin, penicillin and amoxicillin. In general, K. kingae is susceptible to 3rd generation cephalosporins (and combinations with beta-lactam inhibitors), macrolides, fluoroquinolones and trimethoprim-sulfamethoxazole.
In the case of our patient, pediatric infectious disease was consulted and her antibiotic therapy was changed to IV cefazolin. She was discharged home with PO cephalexin for 3 weeks. On return to clinic, she was healing well with no complications.
-Anu Abraham, MD, is a first year Anatomic and Clinical Pathology resident at the University of Mississippi Medical Center.
-Lisa Stempak, MD, is an Assistant Professor of Pathology at the University of Mississippi Medical Center in Jackson, MS. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. She is the Director of Clinical Pathology as well as the Microbiology and Serology Laboratories. Her interests include infectious disease histology, process and quality improvement and resident education.