# Discrimination of Bacteria Belonging to Bacillus cereus Group at Species Level by Fourier Transform Infrared Spectroscopy

## TL;DR

This study shows that FTIR spectroscopy can quickly and accurately tell apart closely related bacteria in the Bacillus cereus group.

## Contribution

The paper introduces FTIR spectroscopy as a novel rapid method for species-level discrimination within the Bacillus cereus group.

## Key findings

- FTIR spectroscopy successfully distinguished B. anthracis from other species in the B. cereus group.
- The method also separated B. cereus sensu stricto from B. thuringiensis with minimal overlap.
- The results suggest FTIR could complement molecular methods in food safety and veterinary microbiology.

## Abstract

The Bacillus cereus group (B. cereus group) comprises several closely related species that share high genetic similarity but display markedly different phenotypic traits and pathogenic potential. Reliable and rapid discrimination at the species level remains challenging using conventional microbiological and molecular methods. In this study, Fourier Transform Infrared (FTIR) spectroscopy was evaluated as a rapid phenotypic approach to differentiate seven members of the Bacillus cereus sensu stricto (B. cereus s.s.), Bacillus anthracis (B. anthracis), Bacillus thuringiensis (B. thuringensis), Bacillus mycoides (B. mycoides), Bacillus toyonensis (B. toyonensis), Bacillus wiedmannii (B. wiedmannii) and Bacillus weihenstephanensis (B. weihenstephanensis). A collection of 190 isolates previously characterized by whole genome sequencing was analyzed using the IR Biotyper system. Spectral data were processed through multivariate analyses, including principal component analysis and linear discriminant analysis, following a hierarchical classification strategy. FTIR spectroscopy enabled clear discrimination of B. anthracis from other members of the B. cereus group and allowed the separation of several additional species based on distinct spectral signatures. A further discrimination step permitted differentiation between B. cereus sensu stricto and B. thuringiensis, with minimal overlap. These findings demonstrate that FTIR spectroscopy represents a promising and rapid tool for species-level discrimination within the B. cereus group. While the results should be considered preliminary for species represented by a limited number of isolates, this approach shows strong potential as a complementary method to molecular techniques in routine diagnostics in food safety and veterinary microbiology.