Clinical Outcomes and Molecular Characteristics of <i>Bacteroides fragilis</i> Infections

<i>Bacteroides fragilis</i> is the most common opportunistic anaerobic pathogen. In the absence of appropriate antimicrobial therapy, mortality rates associated with <i>B. fragilis</i> group infections can reach as high as 50%. Therefore, we aimed to elucidate the clinical characteristics and outcomes of <i>B. fragilis</i> infections and the molecular genetic characteristics of <i>B. fragilis</i> isolates. Forty <i>B. fragilis</i> clinical isolates were collected at Hanyang University Hospital between January 2022 and December 2023. Antimicrobial susceptibility was tested using the agar dilution method. Whole-genome sequencing was conducted using the Illumina platform (Illumina, San Diego, CA, USA). Various multilocus sequence types of <i>B. fragilis</i> were identified, including ST149 (N=4), ST11 (N=4), ST1 (N=3), ST21 (N=2), and ST157 (N=1). The insertion sequence (IS) IS<i>1187</i>, located upstream of <i>cfiA</i>, was associated with high-level carbapenem resistance in the ST157 isolate. <i>B. fragilis</i> toxin genes (bft ) were identified in 30% of isolates. The most common comorbidities were diabetes mellitus (26.5%) and non-metastatic cancer (23.5%). Five patients (14.7%) died within 30 days, and two (5.9%) deaths were directly attributable to <i>B. fragilis</i> infection. The emergence of high-level MIC carbapenem-resistant <i>B. fragilis</i> ST157 has led to caution in the presence of <i>B. fragilis</i> infections.