# Genetic diversity and virulence of Bacillus cereus group isolates from bloodstream infections

## TL;DR

This study explores the genetic diversity and virulence of Bacillus cereus strains causing bloodstream infections in Japanese hospitals, revealing multiple infection sources and distinct virulence profiles.

## Contribution

The study provides new insights into the genetic and virulence characteristics of B. cereus isolates from bloodstream infections in Japan.

## Key findings

- Core-genome SNP analysis revealed significant genetic diversity among isolates, indicating multiple independent infection sources.
- PanC clades III and IV were predominant, with distinct virulence gene profiles including hbl operon and cereulide synthetase genes.
- One isolate had a rare capsule gene operon, and 50% of catheter-related isolates showed biofilm formation ability.

## Abstract

Bacillus cereus catheter-related bloodstream infections (CRBSIs) are an increasing concern in Japanese hospitals. Although their clinical characteristics have been explored, the genetic relationships and virulence profiles of B. cereus isolates from CRBSIs remain understudied. Here, using advanced genomic techniques, we investigated the genetic diversity, phylogenetic relationships, and virulence profiles of B. cereus isolates from patients with bloodstream infections. We analyzed 28 B. cereus group strains isolated from blood samples at the University of Tokyo Hospital between 2005 and 2017 using whole-genome sequencing, core-genome single-nucleotide polymorphism (SNP) typing, and virulence gene profiling. Core-genome SNP analysis revealed significant genetic diversity among the isolates, suggesting multiple independent sources of infection. The isolates predominantly belonged to panC clades III and IV, with distinct virulence gene profiles. All panC clade III isolates contained hbl operon genes, whereas four isolates from clade IV harbored cereulide synthetase genes (cesABCD). One isolate possessed a capsule gene operon (capBCADE), a rare finding among clinical B. cereus strains. Biofilm formation ability was observed in 50% of catheter-related isolates, although this ability was not significantly different from that of the noncatheter-related isolates.

This study provides novel insights into the genetic diversity and virulence potential of B. cereus strains causing bloodstream infections in a Japanese hospital setting. These findings suggest diverse infection pathways and highlight the importance of continuous molecular epidemiological surveillance for effective infection control.