Journal
ULTRASONICS SONOCHEMISTRY
Volume 21, Issue 1, Pages 446-453Publisher
ELSEVIER
DOI: 10.1016/j.ultsonch.2013.06.006
Keywords
High-power ultrasound; Bacteria inactivation; Enterobacter aerogenes; Bacillus subtilis; Staphylococcus epidermidis; Bacterial capsule
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Funding
- New Zealand China Food Safety Scholarship
- New Zealand Ministry of Foreign Affair and Trade
- University of Auckland [3702372]
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The aim of this study was to determine the effects of high-intensity low-frequency (20 kHz) ultrasound treatment on the viability of bacteria suspension. More specifically, we have investigated the relationship between the deactivation efficiency and the physical (size, hydrophobicity) and biological (gram-status, growth phase) properties of the microbes. Enterobacter aerogenes, Bacillus subtilis, Staphylococcus epidermidis, S. epidermidis SK and Staphylococcus pseudintermedius were chosen for this study owing to their varying physical and biological properties. The survival ratio of the bacteria suspension was measured as a function of the ultrasound power (up to 13 W) for a constant sonication time of 20 min. Transmission electron microscopy was used to evaluate the ultrasound-induced damages to the microbes. Ultrasound treatment resulted in lethal damage to E. aerogenes and B. subtilis (up to 4.5-log reduction), whereas Staphylococcus spp. were not affected noticeably. Further, E. aerogenes suspensions were more sensitive to ultrasonication in exponential growth phase than when they were in stationary phase. The results of this study demonstrate that the main reason for bacterial resistance to ultrasonic deactivation is due to the properties of the bacterial capsule. Microbes with a thicker and soft capsule are highly resistant to ultrasonic deactivation process. (C) 2013 Published by Elsevier B.V.
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