Photo Quiz: a Sticky Foe

PHOTO QUIZ

A 27-year-old female of Filipino origin, who had entered the country 2 years before and not travelled abroad, was admitted to the Emergency Department suffering from a 3-day fever and pain in the right knee. Previous relevant medical history included myasthenia gravis, for which she was being treated with azathioprine and prednisone.

Physical examination revealed functional impairment, limiting dorsal knee flexion as well as joint swelling with no further significant findings. Knee X-ray did not show any abnormalities. Blood tests showed increased levels of C-reactive protein of 146 mg/liter (0 to 0.5 mg/liter), procalcitonin of 22.30 ng/mL (0 to 0.5 ng/mL), and severe leukopenia of 500 leucocytes/μL ([3.90 to 10.20] × 10³/μL).

Two sets of blood cultures were collected and an arthrocentesis was performed. The Gram stain of the synovial fluid revealed Gram-negative bacilli with a prominent capsule. The patient was diagnosed with septic arthritis and empirically treated with ceftriaxone (2 g every 24 h). Blood cultures were also positive, showing Gram-negative bacilli in the Gram stain.

Twenty-four hours later, a rod-shaped bacterium grew in the blood and chocolate agar cultures of both the synovial fluid and the blood cultures. The colonies presented a mucous phenotype and generated a viscous string when stretching with inoculation loop (Fig. 1). They were both identified through matrix-assisted laser desorption ionization–time of flight spectroscopy and were tested for antibiotic susceptibility.

FIG 1.

Mucoid colony isolated from synovial fluid.