Optimizing MALDI-TOF Mass Spectrometry for the Identification of Bacillus cereus: The Impact of Sporulation and Cultivation Time

Bacillus cereus is a significant foodborne pathogen that presents a critical challenge in food safety due to its ability to form resistant spores and produce various toxins. The potential for severe food poisoning makes rapid and accurate identification of this pathogen essential. Conventional microbiological methods for B. cereus identification rely on morphological characteristics and biochemical tests, requiring extensive time and labor. However, even automated biochemical systems like VITEK2, while providing reliable results, still require up to 16 h for analysis and complex sample preparation procedures. MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight) mass spectrometry utilizes laser-induced ionization of bacterial proteins and subsequent time-of-flight analysis to generate unique mass spectral patterns. This established analytical technique for bacterial identification offers exceptional speed and simplicity through direct protein profiling. In this study, we optimized MALDI-TOF analysis conditions for B. cereus identification by examining various cultivation times. Our results demonstrated complete species-level identification accuracy with MALDI-TOF scores ≥ 2.0 with 12-h cultures, matching the reliability of VITEK2 while significantly reducing processing time. The identification rates decreased significantly from 100% at 12 h to 73.3% at 24 h and 50% at 48 h of incubation, correlating directly with increased spore formation. Detailed analysis at 4-h intervals revealed that high identification rates (93.3%) were maintained during 16 h of cultivation before declining significantly. This study establishes MALDI-TOF as a reliable and efficient tool for rapid B. cereus identification, representing a significant advancement in food safety diagnostics with potential time savings of more than 50% compared to conventional methods.