(563a) Synergistic Effect of Low Power Ultrasonication and Antimicrobial Peptide Action in Deactivation of  Listeria Monocytogenes

Ultrasound is a relatively new method of food sterilization. Low intensity ultrasound can form transient pores in cell membranes due to shock waves generated by collapse of bubbles that are formed by cavitation. In conventional sterilization using ultrasound, the threshold of power needed for deactivation of microorganisms by thinning and rupture of cell membranes is very high. As a result, conventional ultrasonic sterilization may not be cost effective and may also result in loss of texture of food product. Since antimicrobial peptides kill bacteria by pore formation in cell membranes, transient pores formed by low power ultrasonication should result in enhancement of antimicrobial activity. Because of its relatively gentle action (low intensity), low frequency ultrasound is expected to have no adverse effect on food texture. Experiments were conducted for deactivation of L. monocytogenes using a naturally occurring antimicrobial peptide (AMP) melittin in the absence as well as in the presence of ultrasonication. In the absence of AMP melittin, ultrasonication has very small effect on cell density upto a power level of 40. However, at a higher power level of 60, we observed a dramatic decrease in cell density which implies cell lysis. At low AMP concentration, low power ultrasonication does not improve the antimicrobial activity. At high AMP concentrations, however, AMP was found to completely inactivate L. monocytogenes. The synergistic effect of AMP with ultrasonication was found to be the maximum at AMP concentration of 0.78 μg/ml of melittin. A dramatic decrease in 2 orders of magnitude in cell density was observed for ultrasonication in the presence of 0.78 μg/ml of melittin compared to either ultrasonication alone or AMP action alone. This clearly demonstrates synergistic effect of ultrasonication and AMP for pore formation in cell membrane. A mathematical model was developed to describe the formation of transient pores in cell membranes as a result of cavitation and its effect on pore formation and rupture of cell membrane due to antimicrobial peptide insertion to explain this synergy.