Synergistic effect of low power ultrasonication on antimicrobial activity of melittin against Listeria monocytogenes

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 ultrasound is expected to have no adverse effect on food texture. Experiments were conducted for deactivation of pure culture of L. monocytogenes using a model system of 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 W. However, at a higher power level of 60 W, a dramatic decrease in cell density was observed which implied cell lysis. At low AMP concentration, low power ultrasonication did 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.