Supporting data for<b> </b><b>Antimicrobial resistance in </b><b><i>Bacteroides fragilis</i></b><b> </b><b>group organisms</b>

Using MIC as a reference standard, the consistency of DDT interpretation at different standard breakpoints was compared. The antimicrobial susceptibility levels of BFG strains in Hong Kong were updated, showing a significant increase in resistance to imipenem and metronidazole, particularly among non-<i>fragilis Bacteroides</i> and <i>Parabacteroides</i> species.</p><p><br></p><p dir="ltr">To compare the detection capabilities of three susceptibility testing methods for metronidazole resistance determinants (<i>nim</i>) in BFG isolates using fastidious anaerobe agar with horse blood (FAA-HB) and brucella blood agar (BBA), a challenging collection of 40 clinical isolates (27 <i>nim</i>-positive and 13 <i>nim</i>-negative) was selected.

The FAA-HB DDT is a reliable method for detecting <i>nim</i> genes in BFG isolates.</p><p><br></p><p dir="ltr">To comprehensively evaluate the latest EUCAST DDT method, a challenging collection of 120 clinical BFG isolates was selected to compare DDT and agar dilution methods on FAA-HB against metronidazole, meropenem, and linezolid, and to assess the correlation between the DDT and related resistance genes. This method provides a rapid, convenient, and cost-effective alternative for key resistance monitoring of metronidazole, meropenem, and linezolid.</p><p><br></p><p dir="ltr">Next-generation sequencing of 120 clinical BFG isolates revealed diversity in taxonomy, genomes, and antimicrobial resistance, including associated mobile genetic elements, with a primary focus on resistance to metronidazole, meropenem, and linezolid. <i>nimL</i> as a novel metronidazole resistance determinant and predominant variant, carried by a putative transferable IME element.

Besides <i>cfiA</i>, <i>bla</i>_{<em>OXA-347</em>} may also contribute to carbapenem resistance carried by mobile genetic elements. Linezolid resistance caused by <i>cfr/cfr-like</i> genes is relatively rare in BFG strains. Phylogenetic and comparative genomic analyses support its transferability and highlight its potential presence in clinically relevant anaerobes via horizontal gene transfer.</p><p><br></p><p dir="ltr">In summary, we updated the prevalence of BFG clinical strains in Hong Kong, comprehensively evaluated the latest EUCAST DDT methodology, and confirmed its feasibility in clinical laboratories.

Furthermore, genomic analysis revealed potential resistance mechanisms and transmission pathways of BFG to key antibiotics.</p>