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

The <i>Bacillus cereus</i> group (<i>B. cereus</i> 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 <i>Bacillus cereus</i> sensu stricto (<i>B. cereus</i> s.s.), <i>Bacillus anthracis</i> (<i>B. anthracis</i>), <i>Bacillus thuringiensis</i> (<i>B. thuringensis</i>), <i>Bacillus mycoides</i> (<i>B. mycoides</i>), <i>Bacillus toyonensis</i> (<i>B. toyonensis</i>), <i>Bacillus wiedmannii</i> (<i>B. wiedmannii</i>) and <i>Bacillus weihenstephanensis</i> (<i>B. weihenstephanensis</i>). 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 <i>B. anthracis</i> from other members of the <i>B. cereus</i> group and allowed the separation of several additional species based on distinct spectral signatures. A further discrimination step permitted differentiation between <i>B. cereus</i> sensu stricto and <i>B. thuringiensis</i>, with minimal overlap. These findings demonstrate that FTIR spectroscopy represents a promising and rapid tool for species-level discrimination within the <i>B. cereus</i> 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.