Bacterial resistance to ultrasonic waves under pressure at nonlethal (manosonication) and lethal (manothermosonication) temperatures.

The decimal reduction times of Streptococcus faecium, Listeria monocytogenes, Salmonella enteritidis, and Aeromonas hydrophila corresponding to heat treatment at 62 degrees C were 7.1, 0.34, 0.024, and 0.0096 min, and those corresponding to manosonication treatment (40 degrees C, 200 kPa, 117 microm) were 4.0, 1.5, 0.86, and 0.90 min, respectively. The manosonication decimal reduction times of the four species investigated decreased sixfold when the amplitude was increased from 62 to 150 microm and fivefold when the relative pressure was raised from 0 to 400 kPa. In L. monocytogenes, S. enteritidis, and A. hydrophila, the lethal effect of manothermosonication was the result of the addition of the lethal effects of heat and manosonication, whereas in S. faecium it was a synergistic effect.