Isolation and identification of two highly virulent Glaesserella parasuis serovar 7 strains in China

Glaesserella parasuis (G. parasuis), the etiological agent of Glässer' s disease, is a gram-negative bacterium and a common commensal in the upper respiratory tract of pigs, which can lead to fibrinous polyserositis, meningitis and polyarthritis. In this study, two highly virulent G. parasuis strains belongs to serovar 7, which is normally considered as an avirulent serovar of G. parasuis, were isolated from diseased pigs in China, named as vHPS7 and aHPS7. Animal experiments revealed that vHPS7 and aHPS7 were highly virulent and could lead the death of mice as that of Nagasaki. Cell adhesion and invasion assays showed that the ability of adhesion and invasion of these two serovar 7 isolates is significantly higher than that of non-virulent serovar 7 strains. To further investigate the phylogenic evolution of G. parasuis, a pan-genome analysis was performed and we found that the G. parasuis strains have high variable "open" pan-genome, especially, these two serovar 7 isolates belongs to different clade with classic virulent strains. In addition, the virulence factors of these isolates were predicted in VFDB and we found these two isolates have a similar profile with standard virulent serovar 5 strains rather than non-virulent serotype 7 isolates. Our data indicating that the "non-virulent" serovar 7 of G. parasuis is becoming a potential risk, and these genomic characterization and potential virulence factors will provide ways to further understand the mechanisms underlying pathogenicity of G. parasuis.