Synergistic Effects Between Chitooligosaccharide–Epigallocatechin Gallate Conjugate and Nisin on Inhibition of Seafood-Associated Vibrio spp., Aeromonas spp., and Shewanella spp.

Ready-to-cook Asian moon scallop (RAM) may harbor seafood-associated spoilage and opportunistic pathogenic bacteria, leading to quality deterioration and food safety concerns. This study investigated the microbiological diversity, virulence-associated phenotypes, and antibacterial activity of chitooligosaccharide–epigallocatechin gallate conjugate (CEGC) combined with nisin against seafood-associated bacteria isolated from RAM. A total of 102 bacterial isolates were subjected to identification by MALDI-TOF/MS, with Vibrio, Aeromonas, and Shewanella as the predominant genera. Several isolates exhibited proteolytic and hemolytic activities, indicating spoilage potential and virulence-associated traits. Multivariate analysis showed that bacterial isolates differed widely in their antimicrobial susceptibility and virulence-associated phenotypes. Checkerboard assays demonstrated synergistic effects between CEGC and nisin against Vibrio parahaemolyticus and Vibrio fluvialis (FICI = 0.50). The additive effects were observed for the remaining strains, except an indifferent effect (FICI = 1.06) was found for A. hydrophila. The combined treatment markedly inhibited bacterial growth and biofilm formation, achieving approximately 95% biofilm reduction in V. parahaemolyticus. Confocal laser scanning microscopy and scanning electron microscopy revealed severe membrane disruption, increased permeability, cellular deformation, and collapse of biofilm architecture. Furthermore, CEGC–nisin effectively suppressed V. parahaemolyticus growth in cold-stored RAM. These findings demonstrate that CEGC combined with nisin is a promising natural antimicrobial strategy for improving seafood safety and reducing microbial spoilage in ready-to-cook seafood products.