Epidemiological and comparative genomic analysis of pathogenic Glaesserella parasuis from livestock agriculture in Shandong, China

<i>Glaesserella parasuis</i> (<i>G. parasuis</i>) is the causative agent of Glässer's disease, posing a significant economic threat to the livestock agriculture. The present study aimed to investigate the prevalence of <i>G. parasuis</i> in six regions of Shandong Province, China, from June 2023 to November 2024, and to analyze the whole genome of <i>G. parasuis</i> isolates using whole genome sequencing (WGS). This study conducted a comprehensive analysis of the isolates, encompassing antibiotic resistance profiling, virulence gene detection, multilocus sequence typing (MLST), prophage detection, and pan-genome analysis. The prevalence of <i>G. parasuis</i> ranged from 10.8 to 26.5% across different cities in Shandong Province, exhibiting significant seasonal variation (<i>p</i> < 0.01). Among the 45 isolates, serovar 4 accounted for the highest proportion (40%). Antibiotic resistance testing revealed that 55.6% of isolates demonstrated multidrug-resistance (MDR). WGS analysis revealed that 18 distinct sequence types (STs) were identified across the 45 isolates, including 13 newly discovered STs. Notably, all isolates possessed complete prophage sequences. Pan-genome and phylogenetic analysis of 145 <i>G. parasuis</i> strains indicated that <i>G. parasuis</i> possesses an open pan-genome with genetic diversity. In summary, these data enhance our understanding of the molecular characteristics and epidemiological risks of <i>G. parasuis</i> in Shandong Province, China, particularly regarding livestock agriculture.