Dual-species biofilms formation of Vibrio parahaemolyticus and Shewanella putrefaciens and their tolerance to photodynamic inactivation

Bacteria frequently coexist in complex mixed-species biofilms, and the interspecies interactions highly determine their structure and sensitivity to external stress. Using a dual-species biofilms formed by the pathogen V. parahaemolyticus and spoilage S. putrefaciens, this study characterized the dynamic formation process, spatial structure arrangement, cell viability and EPS components of the biofilms, as well as investigated their response to the curcumin-mediated blue light-emitting diode (LED) photodynamic inactivation (PDI). Results showed that V. parahaemolyticus and S. putrefaciens cooperatively interacted with each other in the dual-species biofilms. Consequently, such relationship increased the cell viability, EPS content and biomass of the biofilms compared to the corresponding mono-species biofilms. Meanwhile, V. parahaemolyticus and S. putrefaciens constructed an intermixed spatial arrangement, which facilitated the communities to fully communicate and hence reinforce their cooperation. On this basis, the dual-species biofilms presented lower sensitivity to PDI than mono-species biofilms, supported by that their biomass and cell viability were maximally reduced by <35%, while those of the mono-species biofilms were eradicated by >80% after the PDI treatment. As a result, this study deepens our understanding of the interactions between food-borne pathogens and spoilage bacteria and their sensitivity to PDI, which is helpful for developing effective strategies to control the mixed-species biofilms.