Comparison with Streptococcus agalactiae Isolates from Humans Reveals Genotypic and Phenotypic Characteristics of Isolates from Companion Animal-origin

This study assessed whether Streptococcus agalactiae isolates from companion animals are different from isolates of human origin. Beta-hemolytic S. agalactiae were 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/genotyping. Twenty non-invasive isolates recovered from animals together with fifteen non-invasive isolates from adult humans were comparatively analyzed in this study. We found significant differences in virulence gene profile of bca-rib-lmb-cylE (40.0% vs. 93.3%) and possession of bac (30.0% vs. 0%) between animal-origin/human-origin non-invasive strains. We observed significant difference in the distribution of CC1 between the two non-invasive populations. There were significant differences in 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 different features, in terms of virulence gene profile, CC, and AMR genotype/phenotype, of non-invasive isolates of animal-origin compared to those of human-origin.