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Glaesserella parasuis is a commensal bacterial organism found in the upper respiratory tract of healthy pigs and the etiological agent of Glässer's disease, which causes severe economic losses in the swine industry. This study aimed to better understand the epidemiological characteristics of this opportunistic pathogen. We investigated the prevalence and distribution of sequence types (STs), serovars, antimicrobial resistance genes (ARGs), and potential virulence factors (VFs) in 764 G . parasuis isolates collected from diseased and healthy pigs from 19 countries, including China. Multilocus sequence typing showed a high degree of variation with 334 STs, of which 93 were not previously recognized. Phylogenetic analysis revealed two major clades distinguished by isolation year, source, country, and serovar. The dominant serovars of G. parasuis were serovars 4 (19.50%), 7 (15.97%), 5/12 (13.87%), and 13 (12.30%). Serovar 7 gradually became one of the dominant serovars in G. parasuis with more VFs and fewer ARGs. Serovars 4 and 5/12 were the most frequent serovars in diseased pigs, whereas serovars 2, 8, and 11 were predominant in healthy pigs. Serovars 7 and 13 possessed more VFs than the other serovars. This study provides novel insights into the global prevalence and epidemiology of G. parasuis and valuable clues for further investigation into the pathogenicity of G. parasuis , which will facilitate the development of effective vaccines.IMPORTANCE Glaesserella parasuis is a clinically important gram-negative opportunistic pathogen, which causes serious financial losses in swine industry on a global scale. No vaccine is known that provides cross-protection against all 15 serovars; furthermore, the correlation between serovar and virulence is largely unknown. This study provides a large number of sequenced strains in 19 countries and compares the genomic diversity of G. parasuis between diseased and healthy pigs. We found a slight change in the dominant serovar of G. parasuis in the world, with serovar 7 gradually emerging as one of the predominant serovars. The observed higher average number of VFs in this particular serovar strain challenges the previously held notion that serovar 7 is non-virulent, indicating a more complex virulence landscape than previously understood. Our analysis indicating that six ARGs [ tet (B), sul2 , aph(3')-Ia , aph (6)-Id , bla ROB-1 , and aph(3'')-Ib ] are likely to be transmitted horizontally in their entirety. By analyzing VFs, we provided an improved understanding of the virulence of G. parasuis , and these key findings suggest that vaccine development will be challenging.

Integrative conjugative elements (ICEs) are important carriers for disseminating resistance genes. We have previously reported a novel element ICE Hpa1 carrying seven antibiotic resistance genes, which could be self-transmissible relying on the novel T4SS. To identify novel ICE Hpa1 variants from 211 strains and novel T4SS encoded in ICE Hpa1 , and to explore the relationships in these ICEs, four complete sequences of ICEs were identified by WGS analysis and antimicrobial susceptibility testing was determined by broth microdilution. In addition, a comparative analysis of these ICEs was conducted with bioinformatic tools, and the transfer abilities of these ICEs were confirmed by conjugation. Four ICE Hpa1 variants ICE Gpa1818 , ICE Gpa1808 , ICE Gpa1807 , and ICE Gpa1815 with different resistance gene profiles were characterized, and their hosts showed different resistance spectrums. All ICEs shared the same backbone and were inserted into the tRNA Leu site, and all resistance regions were inserted into the same target site between the accessory and integration regions. This study analyzed complete sequences of ICEs from the ICE Hpa1 family and identified novel T4SS and insertion element IS Gpa2 . Diverse resistance genes extensively exist in these ICEs, serving as a reservoir for resistance genes and facilitating their dissemination., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sun, Zhang, Miao, Zhai, Pan, Yuan, Yan, Wu and Hu.)

What Is Already Known on This Topic?: Streptococcus suis ( S. suis ) is a zoonotic pathogen causing disease in humans and animals, and the emergence of its increased resistance to antimicrobial agents has become a significant challenge in many countries., What Is Added by This Report?: Using whole genome sequencing data to accurately predict antimicrobial resistance determinants, it was found that the prevalence of antimicrobial resistance genes was higher in the pig isolates of S. suis than in the human isolates and that the prevalence of these genes varied with serotype., What Are the Implications for Public Health Practice?: The data regarding S. suis antimicrobial resistance will help guide rational drug use in the clinic to better protect the health of humans and animals., Competing Interests: No conflicts of interest., (Copyright and License information: Editorial Office of CCDCW, Chinese Center for Disease Control and Prevention 2021.)