Abstract:
Objective To understand the serotype distribution and genomic characteristics of clinical Streptococcus agalactiae strains, and provide evidence for the prevention and treatment of S. agalactiae infection.
Methods A total of 177 clinical strains of S. agalactiae, collected in our laboratory between 2016 and 2023, were used for serotype identification with multiplex polymerase chain reaction (PCR), sequence type (ST) identification was conducted using PCR, and 26 strains were randomly selected from each serotype for high-throughput genome sequencing. The genomic data were used for serotype verification, ST typing, phylogenetic analysis, and the prediction of virulence and resistance genes.
Results PCR identified six serotypes (Ⅰa, Ⅰb, Ⅱ, Ⅲ, Ⅳ, and Ⅴ), with Ⅰb, Ⅴ, and Ⅲ types accounting for 90.40%. Genomic typing of 26 strains revealed 7 serotypes (1 untyped), some strains had inconsistent typing results with PCR. In the 177 strains, 23 STs and 8 clonal complexes were detected. The 26 sequenced strains were classified into 13 distinct STs. Phylogenetic analysis showed that serotype Ⅰb strains exhibited greater genetic conservation. A total of 54 virulence genes were predicted, which are associated with functions such as adhesion and exotoxin production. The strains carried 16 antimicrobial resistance genes, with mreA and Saga_mprF constituting core genetic determinants of basal resistance. Many strains carried tetracycline resistance gene tetM and macrolide resistance gene ermB.
Conclusion This study analyzed the predominant serotypes (types Ⅰb, Ⅴ, and Ⅲ), STs and genomic characteristics of S. agalactiae, and revealed the distribution patterns of its virulence and resistance genes. It is essential to strengthen the surveillance for S. agalactiae serotype distribution and drug resistance, improve typing methodologies in the future to provide evidence for vaccine development and infection prevention strategies and reduce the disease burden associated with S. agalactiae infection.
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