Diagnostic challenges within the Bacillus cereus-group: finding the beast without teeth

Area of Science:

• Microbiology
• Genomics
• Bacterial Pathogenesis

Background:

• The Bacillus cereus group encompasses diverse species, ranging from harmless contaminants to the virulent Bacillus anthracis.
• Standard diagnostic methods often struggle to differentiate closely related species within this group.

Purpose of the Study:

• To evaluate the accuracy of various identification methods for Bacillus cereus group isolates.
• To highlight discrepancies between standard and advanced techniques in species delineation.

Main Methods:

• Whole genome sequencing (WGS) for precise genetic analysis.
• Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) with standard and alternative databases.
• Biochemical phenotyping and diagnostic PCR.

Main Results:

• WGS identified Bacillus anthracis strains lacking typical virulence plasmids, alongside other species like B. paranthracis, B. cereus sensu stricto, and B. thuringiensis.
• Conflicting species identification results were observed across different methods, including MALDI-TOF MS, biochemical tests, and PCR.
• One isolate represented a novel species, Bacillus basilensis sp. nov.

Conclusions:

• Standard microbiological diagnostics face significant challenges in accurately identifying Bacillus cereus group species, particularly avirulent Bacillus anthracis.
• WGS and advanced MALDI-TOF MS databases provide superior accuracy but are not yet routine clinical tools.
• Discrepancies underscore the need for improved diagnostic strategies for this complex bacterial group.