Dysgonomonas capnocytophagoides Bacteremia in a Patient With Stage IV Colon Adenocarcinoma

Dysgonomonas capnocytophagoides bacteremia is a rare clinical entity described in only five case reports. Difficulties in the identification and intrinsic multidrug resistance (MDR) of the organism make diagnosis and treatment challenging. We present a case of D. capnocytophagoides bacteremia which highlights the diagnostic and treatment challenges posed by this organism. The case also contributes to the nascent understanding of the clinical profile of patients with D. capnocytophagoides infection and the antimicrobial susceptibility of the organism. A 56-year-old male with advanced colon adenocarcinoma on palliative fluorouracil, leucovorin, and irinotecan (FOLFIRI) presented with abdominal pain. He had been discharged recently following an ICU admission for neutropenic fever with diarrhea and polymicrobial bacteremia resulting in sepsis. Diarrhea resolved during hospitalization. Mediport was retained, surveillance blood cultures remained negative, and he completed 14 days of levofloxacin. Upon readmission for abdominal pain, vital signs were normal and neutropenia had resolved. A Gram-negative rod grew from blood cultures drawn peripherally and from the port with no differential time-to-positivity. Multiple testing platforms were used in an attempt to identify the organism, to include the VERIGENE® Gram-negative blood culture test, matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, VITEK ® 2 GN ID, and the Thermo Scientific™ RapID™ NH System (Thermo Scientific, Waltham, MA). Test results from all platforms were either inconclusive or contradictory in their identification of the organism, making the determination of appropriate treatment difficult. Given inconsistent results on multiple testing platforms, the isolate was sent for whole genome sequencing (WGS). Additional workup performed during the hospitalization included a diagnostic paracentesis without evidence of spontaneous bacterial peritonitis, transesophageal echocardiogram without evidence of infective endocarditis, and dental evaluation without evidence of the infectious source. Abdominal CT showed nonspecific terminal ileitis. He was treated for presumed HACEK bacteremia and was transitioned from piperacillin-tazobactam to ceftriaxone to complete a two-week course at hospital discharge. He also received a seven-day course of doxycycline for concomitant, mild lower extremity cellulitis which resolved during hospitalization. Ultimately, antimicrobial susceptibility testing which resulted following discharge was not consistent with the HACEK organism. Testing demonstrated resistance to multiple antimicrobials including ceftriaxone, as well as susceptibility to trimethoprim-sulfamethoxazole (TMP/SMX). WGS ultimately identified the organism as D. capnocytophagoides. Despite ceftriaxone resistance, he reported feeling well at follow-up with negative surveillance blood cultures. This patient shares several features with the few patients previously identified with D. capnocytophagoides bacteremia, including malignancy, recent neutropenia, and presumed gastrointestinal source. As in the small number of prior reported cases, the organism was difficult to identify leading to delay in diagnosis and treatment. The case demonstrates the importance of critical thinking in the face of contradictory test results. Additionally, based on susceptibility profiles described in prior literature, we suspect doxycycline treated his bacteremia.