What is it about?
Ruminococcus gnavus is an anaerobic gram-positive bacterium that normally inhabits the human gastrointestinal tract. Although it is a common component of the gut microbiota, its role as a human pathogen remains poorly understood, and clinical data on R. gnavus infections are scarce. In this retrospective study conducted at a tertiary care hospital in Japan between 2016 and 2022, we identified 16 cases of R. gnavus infection — 13 cases of bacteremia and 3 cases of intra-abdominal infection. The cases represented 0.3% of all blood culture-positive cases during the study period. The median patient age was 75 years, and the most common underlying conditions were immunosuppression and solid tumors (seven cases each), and a history of gastrointestinal surgery (five cases). Twelve of the 16 cases had an intra-abdominal infection source, and 13 patients presented with gastrointestinal complications including bowel perforation, intra-abdominal abscesses, and peritonitis. Multiple pathogens were detected in six cases, with co-isolated organisms typically being of intestinal origin. Three patients died. Antimicrobial susceptibility testing on eight isolates showed low MICs for penicillin, ampicillin-sulbactam, piperacillin-tazobactam, and metronidazole.
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Why is it important?
Prior to this study, R. gnavus infections had been reported only as individual case reports or small case series. This study provides the largest single-institution case series of R. gnavus infections to date, offering a clearer picture of the typical patient profile, clinical presentation, and antibiotic susceptibility. The identification of R. gnavus has become more feasible with MALDI-TOF mass spectrometry, suggesting that cases may have previously been missed or misidentified. Clinicians should consider R. gnavus as a potential pathogen in patients with immunosuppression, solid tumors, or gastrointestinal disease who present with anaerobic bacteremia or intra-abdominal infection.
Perspectives
When R. gnavus is detected in blood cultures or intra-abdominal specimens, clinicians should actively assess for an underlying gastrointestinal source, as bowel perforation and abscess are common findings. The frequent co-detection of other intestinal pathogens also means that treatment regimens should provide broader anaerobic coverage rather than targeting R. gnavus alone. Penicillin-based agents and metronidazole appear effective against most strains, but further data on antimicrobial susceptibility — particularly for clindamycin and moxifloxacin, which showed variable MICs — are needed. Continued updates to MALDI-TOF mass spectrometry databases will be important for reducing underdiagnosis of this emerging pathogen.
Dr Naoki Watanabe
Hirosaki University
Read the Original
This page is a summary of: Clinical and microbiological characteristics of Ruminococcus gnavus bacteremia and intra-abdominal infection, Anaerobe, February 2024, Elsevier,
DOI: 10.1016/j.anaerobe.2024.102818.
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