Genetic Diversity of Streptococcus agalactiae from Multiple Host Species in China

Streptococcus agalactiae is a serious zoonotic pathogen that causes disease in humans and other animals worldwide. Due to the increasing prevalence of S. agalactiae, as well as the transmission risk of S. agalactiae from animals to human, it was important to identify the serotype diversity and molecular typing population structure of S. agalactiae isolated from human, bovine, rabbit, and fish. Capsular polysaccharide serotypes (CPS), multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE) technologies were used to compare the genetic diversity of 56 S. agalactiae isolates from human, rabbit, bovine, and fish sources in China. We found that two serotypes (Ia, III) existed, with serotype Ia being the most common (85.7%). The 56 isolates were assigned to nine sequence types (STs) and seven clonal complexes (CCs) using MLST. The most common ST was ST891 (35.7%). The ST19 and ST103 were found in two different isolates, while the remaining STs were found in one isolate. A total of 18 PFGE clusters were identified, however, only cluster P was found in both human and bovine isolates. Our findings suggest that serotypes, STs and PFGE, had no obvious correlation with particular host species. However, the similarity of genotypes of S. agalactiae isolated from different host species, speculating cross-infection possibility between them at genetic level.