Purpose: These studies examined the activity of the AMPs hepcidin and nisin against V. vulnificus, V. parahaemolyticus and V. cholerae with and without the application of chemical or physical stressors in vitro and in live oysters.
Methods: In vitro bacterial growth inhibition by hepcidin and nisin with and without EDTA or cold shock was evaluated in microtiter plates and in culture flasks, respectively. Population changes were measured using plate counts and/or optical density. The effectiveness of nisin with and without cold shock and/or EDTA was also tested against V. vulnificus in live oysters. These studies evaluated reductions in both the natural bacterial populations as well as populations in a previously established oyster infection model.
Results: In vitro growth of V. vulnificus was inhibited by hepcidin at various inocula (103-105 CFU/ml), but only at higher hepcidin concentrations (50, 75 and 100 µM). Exposure to nisin alone or in conjunction with EDTA had no effect on in vitro growth or survival of any Vibrio spp evaluated. However, concomitant cold shock, EDTA and nisin exposure resulted in significant (P ≤ 0.035) reductions in culture concentrations for all three Vibrio spp. Natural populations of V. vulnificus in oysters also showed in a reduction (but not significant) of about 1.0 log CFU/ml in response to the synergistic effect of cold shock, EDTA and nisin.
Significance: Results from these studies support the potential application of a hurdle-type postharvest processing treatment for oysters.