# CRISPR1-mediated virulence and erythromycin resistance stabilization drives regional dominance of Streptococcus agalactiae ST10 in China

## TL;DR

This study finds that the CRISPR1 system helps a specific strain of Streptococcus agalactiae dominate in China by stabilizing virulence and antibiotic resistance.

## Contribution

The study identifies CRISPR1 as a novel factor contributing to the regional dominance of ST10 Streptococcus agalactiae in China.

## Key findings

- ST10 was the most common sequence type in both invasive and colonizing isolates from Shanxi, China.
- CRISPR1 was strongly associated with key virulence genes and stable erythromycin resistance in ST10 strains.
- CRISPR1 may enhance ST10 fitness by stabilizing virulence and resistance traits and limiting plasmid acquisition.

## Abstract

Streptococcus agalactiae (Group B Streptococcus, GBS) is a major pathogen of neonatal infections worldwide, with significant geographical variation in its prevalent sequence types (STs). In Shanxi, China, ST10 has emerged as the dominant lineage in perinatal infections, yet the mechanisms underlying its regional dominance remain unclear. This study aimed to investigate the molecular epidemiological basis for the predominance of ST10 in this region.

We analyzed 55 clinical Streptococcus agalactiae isolates (21 invasive, 34 colonizing) collected from a hospital in Shanxi, China. Multilocus sequence typing (MLST) was performed to determine sequence types. Virulence genes and the CRISPR1 (clustered regularly interspaced short palindromic repeats, CRISPR) system were detected by polymerase chain reaction (PCR). Statistical analyses were conducted to assess associations between ST10, CRISPR1, and virulence gene carriage.

ST10 accounted for 50.9% (28/55) of all isolates, predominating in both invasive (13/21, 61.9%) and colonizing (15/34, 44.1%) groups. Invasive ST10 strains universally carried the virulence genes cylE, hylB, scpB, and bca (100%) and exhibited complete erythromycin resistance mediated by ermB (100%). The CRISPR1 system was highly prevalent in ST10 isolates (26/28, 92.9%), and its presence was significantly associated with the virulence genes cylE (69.8% vs 25.0%; P=0.014) and hylB (62.8% vs 16.7%; P=0.012).

The findings delineate a "high-virulence/controlled-resistance" phenotype in the locally dominant ST10, characterized by a conserved virulence gene, stable chromosomal ermB resistance, and a high prevalence of CRISPR1. This suggests CRISPR1 may contribute to the fitness of the ST10 lineage by stabilizing chromosomal virulence and resistance determinants while potentially restricting plasmid acquisition. This study establishes CRISPR1 as a potential key driver of ST10 adaptation and a possible predictive marker for monitoring high-risk clones, providing a rationale for regionally tailored prophylaxis strategies.