We want to thank everyone who stopped by our booth at IDSA and participated in our Guess The Unknown Contest. Below is the correct answer.

Question: A 36 y/o male presents with a week history of fever, associated with a 12 pound weight loss, night sweats, and nonproductive cough.  PEx unremarkable; CT chest revealed necrotizing mediastinal lymphadenopathy and left lower lobe bronchiectasis.  Biopsy of the mediastinal nodes revealed well formed granulomas.  Special stains for acid fast and fungi, gram stain, and routine culture was negative.

Past history:

  • Recurrent MRSA skin abscesses for many years
  • One episode of community acquired pneumonia – no organism
  • identified; defervesced on trimethoprim/sulfamethoxazole
  • Colitis with granulomas on biopsy – diagnosed several years ago



  • WBC 11.7K with 74 segs, 6 bands, 18 lymphs, 2 monos
  • Platelet ct 225K; creatinine 1.4; AST 45, Alkaline phosphatase 200

Clinical Course: The patient was empirically begun on vancomycin and ciprofloxacin for five days without clinical improvement and was switched to meropenem.  Over the next week the fever curve decreased and by the second week of therapy the patient was afebrile.  Meropenem was continued for fourteen days.

One month after being discharged from the hospital the patient noted pain in his left neck with a tender mass. A CT scan of the neck showed multiple necrotizing lymph nodes and a lymph node biopsy revealed well formed granulomas.  Gram stain and special stains were negative but after 7 days, a gram negative rod was identified on BYCE agar.

Name the organism.



Granulibacter bethesdensis is a GNR that has been identified exclusively in patients with Chronic Granulomatous Disease (CGD).  First isolated in 2003, this organism has been identified in the USA, Panama, and Spain. The organism may have active and latent phases, similar to tuberculosis, causing relapsing and recurrent infections.   G. bethesdensis may present with fever, weight loss, and necrotizing lymphadenitis.  Patients are typically ill for weeks to months, in stark contrast to the more acute presentation of S. aureus lymphadenitis in CGD patients. 

The organism can be cultivated on a variety of media such as Middlebrook, BYCE, and fungal, but may take 1-3 weeks before identification can be made.

A clue to the diagnosis and specifically in the case presented is the extensive resistance of G. bethesdensis to penicillins, most cephalosporins, and quinolones.  If the GNR identified had been Serratia, we would have anticipated that the patient would have defervesced with quinolone therapy.  Trimethoprim/sulfamethoxazole (sxt), aminoglycosides, doxycycline, and ceftriaxone show activity in vitro.

The patient presented had recurrent Staphylococcal abscesses and a culture negative pneumonia which responded to SXT.  While this may have been a G. bethesdensis infection, it was more likely a nocardial disease, consistent with one of the more common pathogens experienced by CGD patients.


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