Comparison of Streptococcus agalactiae Isolates from Humans and Companion Animals Reveals Genotypic and Phenotypic Differences.

This study assessed whether Streptococcus agalactiae isolates from companion animals differed from those of human origin. Beta-hemolytic S. agalactiae was collected from a veterinary laboratory center and a university hospital. Strains were identified using 16S rRNA amplicon sequencing and amplification of the species-specific dltS gene. We conducted virulence gene profiling, capsular genotyping, determination of clonal complex (CC), and antimicrobial resistance (AMR) phenotyping or genotyping. The 20 non-invasive isolates obtained from animals and 15 non-invasive isolates from adult humans were comparatively analyzed in this study. We found significant differences in the virulence gene profiles of bca-rib-lmb-cylE (40.0% vs. 93.3%) and the possession of bac (30.0% vs. 0%) between animal-origin and human-origin non-invasive strains. We observed a significant difference in the distribution of CC1 between the two non-invasive populations. There were significant differences in the prevalence of tetracycline resistance genotypes (60.0% vs. 20.0%) and absence of AMR genotypes (30.0% vs. 80.0%), and AMR rates of tetracycline (35.0% vs. 0%) and fluoroquinolone (20.0% vs. 66.7%) between the two non-invasive populations. These observations suggest that there were different features, in terms of virulence gene profile, CC, and AMR genotype/phenotype in the non-invasive isolates of animal origin compared to those of human origin.