[Plasmid characteristics and genome tracing analysis of a bacterial dysentery outbreak in Shandong Province, originating from <i>Shigella sonnei</i> producing extended spectrum β-lactamase].

<b>Objective:</b> To investigate the drug resistance gene characteristics, plasmid characteristics and genome tracing of <i>Shigella sonnei</i> causing a bacillary dysentery outbreak in Shandong Province. <b>Methods:</b> Sixty-five <i>Shigella sonnei</i> strains isolated from a 2021 outbreak in a county of Shandong Province were analyzed using antimicrobial susceptibility testing, whole genome sequencing (WGS), characterization of resistance and virulence genes, plasmid profiling, core genome multilocus sequence typing (cgMLST), and single nucleotide polymorphism (SNP) analysis. <b>Results:</b> All isolates had the same resistance phenotype and genotypes and were multidrug-resistant ESBL-producing <i>Shigella sonnei</i>, carrying important virulence genes. Plasmid analysis revealed a conserved genetic arrangement, <i>pil</i>(<i>M</i>/<i>N</i>/<i>O2</i>/<i>P</i>)-tra(<i>F</i>/<i>H</i>/<i>J</i>/<i>K</i>/<i>N</i>/<i>O</i>/<i>P</i>/<i>Q</i>)-IS<i>Ecp1</i>-<i>bla</i>_CTX-M-14-Tn<i>903</i>-<i>yub</i>(<i>J</i>/<i>I</i>/<i>F</i>/<i>G</i>/<i>E</i>/<i>D</i>), and shared across strains from diverse regions and bacterial species. The cgMLST and SNP analyses demonstrated concordant clustering, with all 65 outbreak-related strains forming a single cluster alongside human-derived strains from Guangxi. <b>Conclusion:</b> The ESBL-producing <i>Shigella sonnei</i> responsible for the outbreak shares a homologous relationship with Guangxi human-derived strains, and the detected resistance plasmids and virulence genes underscore the need to strengthen drug resistance surveillance and genome tracing.