Photoinactivation of bacteriophage MS2, Tulane virus and Vibrio parahaemolyticus in oysters by microencapsulated rose bengal

Bivalve molluscan shellfish such as oysters are important vectors for the transmission of foodborne pathogens including both viruses and bacteria. Photoinactivation provides a cold-sterilization option against the contamination as excited photosensitizers could transfer electronic energy to oxygen molecules producing reactive oxygen species such as singlet oxygen, leading to oxidative damage and death of the pathogens. However, the efficacy of photoinactivation is very often compromised by the presence of food matrix due to the nonselective reactions of short-lived singlet oxygen with organic matter other than the target pathogens. In order to address this issue, we encapsulated a food-grade photosensitizer rose bengal (RB) in alginate microbeads. An extra coating of chitosan effectively prevented the release of RB from the microbeads in seawater, and more importantly, enhanced the selectivity of the photoinactivation via the electrostatic interactions between cationic chitosan and anionic charge of the virus particles (bacteriophage MS2 and Tulane virus) and the Gram-negative bacteria Vibrio parahaemolyticus (V. parahaemolyticus). The treatment of oysters with microencapsulated RB resulted in significantly higher reductions of MS2 phage, Tulane virus and V. parahaemolyticus than free RB and non-RB carrying microbeads (P<0.05) tested with both in vitro and in vivo experimental set-ups. This study demonstrated a new strategy in delivering comprehensively formulated biochemical sanitizers in bivalve shellfish through their natural filter-feeding activity and thereby enhancing the mitigation efficiency of foodborne pathogen contamination.

Automated summary

Bivalve molluscan shellfish such as oysters play an important role in the transmission of foodborne pathogens. Photoinactivation is a potential method for cold sterilization, but its effectiveness is often compromised by the presence of food matrix. To address this issue, the study encapsulated a food-grade photosensitizer, rose bengal (RB), in alginate microbeads and coated them with chitosan to enhance the selectivity of photoinactivation. The treatment of oysters with microencapsulated RB resulted in significantly higher reductions of pathogens compared to free RB and non-RB carrying microbeads, demonstrating a new strategy for delivering biochemical sanitizers in bivalve shellfish to mitigate foodborne pathogen contamination.