# From Gut Commensal to Opportunistic Pathogen: A Narrative Review of Butyricimonas Infections in Humans

## TL;DR

This review summarizes rare Butyricimonas infections in humans, focusing on risk factors, symptoms, treatments, and outcomes.

## Contribution

Compiles and analyzes all reported cases of Butyricimonas infections to guide clinical recognition and management.

## Key findings

- Most cases occurred in older males with malignancy as a common predisposing factor.
- Carbapenems and metronidazole showed high in vitro susceptibility against Butyricimonas isolates.
- Overall mortality was 16.7%, with 8.3% of deaths directly attributed to the infection.

## Abstract

Background/Objectives: Butyricimonas species constitute a genus of Gram-negative, anaerobic bacteria that are part of the human gut microbiota. Infections caused by these organisms are extremely rare in clinical practice. While uncommon in the general population, their occurrence is higher among immunocompromised individuals or patients with significant underlying health conditions. This review aims to compile and analyze all reported cases of human Butyricimonas infections, focusing on epidemiology, microbiological characteristics, antimicrobial resistance patterns, treatment strategies, and associated mortality. Methods: This review was conducted using data retrieved from the PubMed/MEDLINE and Scopus databases. Results: A total of 14 publications described Butyricimonas infections affecting 14 patients. The mean age of those affected was 66.46 years, and 10 (71.4%) were male. The most frequently reported predisposing factor was a history of malignancy, observed in almost one-third of cases (30.8%). Clinically, fever, organ dysfunction, and shock were the most common presentations (fivecases), followed by sepsis and the need for ICU in fourpatients. In vitro studies indicated that the isolates were generally susceptible to carbapenems and metronidazole, with only high resistance levels observed to penicillin. Among the antimicrobial therapies used, carbapenems were the most commonly administered (50%), followed by piperacillin/tazobactam (41.7%) and metronidazole (33.3%). The overall mortality rate across the cohort was 16.7%, with infection-attributable deaths representing 8.3% of cases. Conclusions: Given the potential of Butyricimonas species to cause severe infections, clinicians should consider this organism in patients presenting with unexplained bacteremia or intra-abdominal infections, particularly in the setting of mucosal disruption or immune dysfunction.