Effects of NaCl, glucose, and their combinations on biofilm formation on black tiger shrimp (Penaeus monodon) surfaces by Vibrio parahaemolyticus

The aim of this study was to evaluate the promotive and/or inhibitory effects of NaCl, glucose, their combinations on biofilm formation and quorum sensing (QS) autoinducer-2 (AI-2) production on black tiger shrimp surfaces, using three strains of Vibrio parahaemolyticus. Initially, six different NaCl concentrations (0.5, 1, 2, 3, 4, and 5%) were evaluated for a maximum biofilm formation (∼6.3 log CFU/cm2) at 30 °C. Inhibitory effects of glucose at six different levels (0.005, 0.01, 0.015, 0.02, 0.025, and 0.05%) were then investigated using the NaCl level previously found for a maximal biofilm formation. V. parahaemolyticus formed the best biofilm at 2% NaCl and the least biofilm at 5% NaCl, regardless of vibrio strain. In combination of 2% NaCl and glucose at different levels, the largest biofilm was observed at 0.015%, with the least biofilm seen at 0.05%, regardless of vibrio strain. Addition of salt and glucose more than the optimal level (2% salt and 0.015% glucose at 2% salt) inducted a stepwise inhibition of vibrio growth and biofilm formation in a continuous matter. In the visual evaluation, similar results were observed for vibrio growth, biofilm formation, live/dead cell detection, and quorum sensing.