Purpose: This study aimed to assess the efficacy of high-frequency mechanical vibration for dislodging Salmonella and Enterococcus faecium from processing surfaces under controlled environmental conditions.
Methods: Wheat flour was inoculated with Salmonella Enteritidis PT30 or E. faecium using a glass bead dry transfer method to achieve populations of 6.7 and 6.9 log CFU/g, respectively. After conditioning to an aw of 0.45 in an environmental chamber, the inoculated powder was applied to stainless steel coupons using an electrostatic powder coating gun. The coupons were then treated with two vibration modes and frequencies (28 and 40 kHz) using piezoelectric transducers, then plated on modified TSA or MRS media to enumerate Salmonella and E. faecium, respectively. Also, surfaces were analyzed via scanning electron microscopy.
Results: Populations of Salmonella and E. faecium in the inoculated wheat flour gradually decreased to 6.2 and 4.2 log CFU/g, respectively, after 10 d of conditioning at 45% RH. The electrostatic attachment method yielded significantly (P < 0.05) greater surface attachment for Salmonella (39.1 CFU/cm2) than E. faecium (1.2 CFU/cm2), with significant variations in cell density also observed across the replications. However, HFNA treatment was able to reduce Salmonella populations on the stainless steel coupons by ~69 and 66% at 28 and 40 kHz, respectively, which was confirmed with variable pressure electron microscopy.
Significance: The findings will contribute to understanding the physical characteristics of bacterial attachment to dry surfaces and the potential efficacy of high-frequency mechanical vibration for dry equipment decontamination.