Ruminococcus Gnavus Infection Detected in Ascites Fluid in a Patient with Cirrhosis

Ruminococcus gnavus (R. gnavus) is a gram-positive, anaerobic diplococcus that does not form spores and significantly influences human gut microbiota composition. Its presence in ascitic fluid is exceedingly rare and typically associated with compromised intestinal barriers.

We present a unique case of R. gnavus detected in ascitic fluid from a patient diagnosed with multiple myeloma and liver cirrhosis. Ascitic fluid was subjected to bacterial culture, Gram and Swiss staining, and identification by Bruker mass spectrometry. Antibiotic susceptibility tests were conducted to evaluate resistance patterns.

R. gnavus was identified in the patient's ascitic fluid through bacterial culture and Bruker mass spectrometry. Consistent results were obtained using the Vitek 2 Compact system and two MALDI-TOF MS methods, with a Bruker score of 2.17 and a Vitek MS confidence level of 99.9%, confirming the presence of R. gnavus, which is extremely rare in ascitic fluid. Antibiotic susceptibility testing showed resistance to penicillin, ceftriaxone, vancomycin, linezolid, clindamycin, ciprofloxacin, and levofloxacin.

Disruption of the natural intestinal mucosal barrier can lead to translocation of R. gnavus. In patients with liver cirrhosis, the bacterial load of R. gnavus is also significantly increased. Additionally, patients with multiple myeloma may promote the dominance of R. gnavus through regulation of the gut-brain axis. The combined effect of these factors may explain the presence of this rare bacterium in the ascitic fluid of our patient.