Genomic and pathogenic investigations of serotype 7 population derived from a human patient and pigs.

is one of the important emerging zoonotic pathogens. Serotype 2 is most prevalent in patients worldwide. In the present study, we first isolated one serotype 7 strain GX69 from the blood culture of a patient with septicemia complicated with pneumonia in China. In order to deepen the understanding of serotype 7 population characteristics, we investigated the phylogenetic structure, genomic features, and virulence of serotype 7 population, including 35 strains and 79 genomes. Significant diversities were revealed in serotype 7 population, which were clustered into 22 sequence types (STs), five minimum core genome (MCG) groups, and six lineages. Lineages 1, 3a, and 6 were mainly constituted by genomes from Asia. Genomes of Lineages 2, 3b, and 5a were mainly from Northern America. Most of genomes from Europe (41/48) were clustered into Lineage 5b. In addition to strain GX69, 13 of 21 serotype 7 representative strains were classified as virulent strains using the C57BL/6 mouse model. Virulence-associated genes preferentially present in highly pathogenic serotype 2 strains were not suitable as virulence indicators for serotype 7 strains. Integrative mobilizable elements were widespread and may play a critical role in disseminating antibiotic resistance genes of serotype 7 strains. Our study confirmed serotype 7 is a non-negligible pathotype and deepened the understanding of the population structure of serotype 7, which provided valuable information for the improved surveillance of this serotype.