Antimicrobial susceptibility of Bacteroides fragilis group organisms in Hong Kong, 2020–2021

Abstract

<h3>Objectives</h3><p>This retrospective study analyzed the susceptibility levels of <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/bacteroides-fragilis" title="Learn more about Bacteroides fragilis from ScienceDirect's AI-generated Topic Pages">Bacteroides fragilis</a> group (BFG) in a hospital-based laboratory where <a href="https://www.sciencedirect.com/topics/immunology-and-microbiology/disk-diffusion" title="Learn more about disk diffusion test from ScienceDirect's AI-generated Topic Pages">disk diffusion test</a> (DDT) was routinely performed. Isolates non-susceptible to <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/imipenem" title="Learn more about imipenem from ScienceDirect's AI-generated Topic Pages">imipenem</a> and <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/metronidazole" title="Learn more about metronidazole from ScienceDirect's AI-generated Topic Pages">metronidazole</a> by DDT were further investigated using a gradient method.</p><h3>Methods</h3><p>The DDT and MIC susceptibility data of <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/clindamycin" title="Learn more about clindamycin from ScienceDirect's AI-generated Topic Pages">clindamycin</a>, <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/metronidazole" title="Learn more about metronidazole from ScienceDirect's AI-generated Topic Pages">metronidazole</a>, <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/moxifloxacin" title="Learn more about moxifloxacin from ScienceDirect's AI-generated Topic Pages">moxifloxacin</a> and <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/imipenem" title="Learn more about imipenem from ScienceDirect's AI-generated Topic Pages">imipenem</a> obtained on <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/brucella" title="Learn more about Brucella from ScienceDirect's AI-generated Topic Pages">Brucella</a> blood agar for 1264 non-duplicated isolates during 2020–2021 were analyzed. Species identification was obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry and <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/rna-16s" title="Learn more about 16S rRNA from ScienceDirect's AI-generated Topic Pages">16S rRNA</a> sequencing. Interpretative agreement of DDT results using the 2015 <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/antibiogram" title="Learn more about EUCAST from ScienceDirect's AI-generated Topic Pages">EUCAST</a> tentative and 2021 CA-SFM breakpoints was compared against MIC as the reference.</p><h3>Results</h3><p>The dataset included 604 <em>B. fragilis</em> (483 division I, 121 division II isolates), 415 non-<em>fragilis Bacteroides</em>, 177 <em>Phocaeicola</em> and 68 <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/parabacteroides" title="Learn more about Parabacteroides from ScienceDirect's AI-generated Topic Pages">Parabacteroides</a>. Susceptibility rates for <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/clindamycin" title="Learn more about clindamycin from ScienceDirect's AI-generated Topic Pages">clindamycin</a> (22.1–62.1%) and <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/moxifloxacin" title="Learn more about moxifloxacin from ScienceDirect's AI-generated Topic Pages">moxifloxacin</a> (59.9–80.9%) were low and many had no <a href="https://www.sciencedirect.com/topics/immunology-and-microbiology/zone-of-inhibition" title="Learn more about inhibition zones from ScienceDirect's AI-generated Topic Pages">inhibition zones</a>. At the <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/antibiogram" title="Learn more about EUCAST from ScienceDirect's AI-generated Topic Pages">EUCAST</a> and CA-SFM breakpoints, 83.0 and 89.4% were imipenem-susceptible, and 89.6% and 97.4 were metronidazole-susceptible. MIC testing confirmed 11.4% and 2.8% isolates as imipenem-non-susceptible and metronidazole-resistant, respectively. Significant numbers of false-susceptibility and/or false-resistance results were observed at the CA-SFM breakpoint but not the EUCAST breakpoint. Higher rates of imipenem and/or metronidazole resistance were detected in <em>B. fragilis</em> division II, <em>B. caccae, B. ovatus, B. salyersiae, B. stercoris</em> and <em>Parabacteroides</em>. Co-resistance to imipenem and metronidazole was detected in 3 <em>B. fragilis</em> division II isolates.</p><h3>Conclusions</h3><p>The data demonstrated emerging BFG resistance to several important anti-anaerobic antibiotics and highlights the importance of anaerobic susceptibility testing in clinical laboratories to guide therapy.</p>