Comparative Analysis of Streptococcus Agalactiae S03 and S07 Isolated From Schizothorax Prenanti With Different Antibiotic Resistance and Virulence

Abstract Streptococcus agalactiae (GBS), is an important Gram-positive pathogen of fish aquaculture worldwide. In this study, we performed a comparative analysis of GBS S03 and S07 isolated from Schizothorax prenanti and explored the association between phenotypic antibiotic resistance as well as virulence and the genomic characteristics. Antimicrobial sensitivity tests on 12 common antibiotics using the disc diffusion method revealed that the S03 showed resistance to seven antibiotics, while S07 showed sensitivity to the tested antibiotics. Pathogenicity analysis demonstrated greater virulence of S07 than S03. Then, the occurrence of antibiotic resistance and virulence genes was identified using whole-genome sequence (WGS) of S03 and S07. There were mefE , tetO , lnuB , lsaE , APH3' , and sat-4 resistance genes present only in S03 genome. And just S03 had gyrA and parC genes mutations. In addition to 51 virulence genes in both S03 and S07 genomes, S07 additionally carried virulence genes associated with invasion, such as SAN_1519 , rfbA and cylE genes. There was complete concordance between genotypic evidence and phenotypic characteristics. Virulence factors and phylogenetic analysis showed that S03 and human sources shared an extremely close evolutionary relationship. Our findings provide important proof for using WGS as an effective tool of phenotypic predictions of GBS.