Thermal Injury and Recovery of Bacillus cereus

Area of Science:

• Microbiology
• Food Safety
• Bacterial Physiology

Background:

• Assessing thermal injury in foodborne pathogens is crucial for food safety.
• Bacillus cereus is a common cause of foodborne illness, and its viability after heat treatment needs careful monitoring.

Purpose of the Study:

• To develop a system for measuring thermal injury in Bacillus cereus B4ac.
• To investigate the conditions affecting the viability and recovery of heat-stressed Bacillus cereus cells.

Main Methods:

• Vegetative Bacillus cereus cells were heated and then assessed for sensitivity to pH and NaCl.
• Differential plating on Plate Count Agar (PCA) versus PCA with 2.5% NaCl was used to detect injury.
• Recovery potential was tested using various media formulations, including those with specific inhibitors of protein, DNA, or RNA synthesis.

Main Results:

• Heat-treated Bacillus cereus cells (47°C, 5 min) exhibited decreased viability at pH < 6.3 or > 7.3, and with ≥ 2% NaCl.
• Injury detection was effective using differential plating, while standard enumeration methods (polymyxin B, phenol red) remained unaffected.
• Partial recovery occurred in peptone, Brain Heart Infusion broth, amino acid mixtures, or glucose, particularly when combined with protein or DNA synthesis inhibitors (chloramphenicol, nalidixic acid).
• Optimal recovery temperatures ranged from 20°C to 37°C.
• Recovery was inhibited by RNA synthesis inhibitors (rifampicin) and specific buffer conditions.

Conclusions:

• A reliable method for detecting thermal injury in Bacillus cereus was established.
• Heat-stressed Bacillus cereus cells exhibit specific sensitivities that can be leveraged for detection.
• Cellular repair mechanisms, including protein and DNA synthesis, are vital for recovery from thermal injury, while RNA synthesis appears less critical for this process.