Kinetics and Mechanism of Bacterial Inactivation by Ultrasound Waves and Sonoprotective Effect of Milk Components

Abstract

Inactivation of Escherichia coli and Listeria monocytogenes were investigated in buffer and milk upon treatment with ultrasound waves (USW). In addition, sonoprotective effect of milk components and ultrasound-induced changes in bacterial cells were investigated using scanning electron microscopy (SEM). Bacterial cells were added to phosphate buffer, whole milk, skim milk, or simulated milk ultrafiltrate (SMUF). To determine the sonoprotective effect of milk components, lactose (5%), casein (3%), or β lactoglobulin (0.3%) was added to SMUF. Samples were sonicated with 24 kHz pulse USW while maintaining the system temperature between 30 to 35 °C. Aliquots were drawn at set times during sonication and bacteria were enumerated by surface plating appropriate dilutions on selective and nonselective media plates. Escherichia coli exhibited significantly higher D values in whole (2.43 min) and skim milk (2.41 min) than phosphate buffer (2.19 min). Listeria monocytogenes also showed higher D values in whole (9.31 min) and skim milk (8.61 min) compared to phosphate buffer (7.63 min). Data suggest that milk exerts a sonoprotective effect on these bacteria. Escherichia coli exhibited a log-linear inactivation kinetics followed by tailing whereas L. monocytogenes showed 1st-order kinetics throughout. Among the milk components tested, presence of lactose in SMUF resulted in significantly higher D values than SMUF for both organisms suggesting that lactose was exerting a protective effect on bacteria. SEM images showed that USW caused mechanical damage to the cell wall and cell membrane of bacteria leading to their inactivation.

High Intensity Ultrasound for Salmonella Enteritidis Inactivation in Culture and Liquid Whole Eggs

“…This suggests the protective effect of food components in the LWE samples. The sonoprotective phenomena of foods (such as milk) on bacteria in comparison to buffers have been previously reported (Gera & Doores, 2011;Wrigley & Llorca, 1992;Zenker, Heinz, & Knorr, 2003). Fat content present in milk was earlier shown to reduce bacterial inactivation efficacy of ultrasound compared to fat-free milk (Bermudez-Aguirre & Barbosa-Cánovas, 2008).…”

Engineered biomaterial and biophysical stimulation as combinatorial strategies to address prosthetic infection by pathogenic bacteria

“…Thus, the shock waves and free radicals are believed to contribute majorly toward the antimicrobial effect of ultrasound. 62 However, this effect is largely known to be dependent on the frequency of ultrasound applied. Both the low frequency (<100 kHz) and high frequency ultrasound are known to generate microcavitation.…”

“…Another side effect of the collapse of acoustic cavitation is the development of localized high temperatures that leads to the generation of free radicals. Thus, the shock waves and free radicals are believed to contribute majorly toward the antimicrobial effect of ultrasound . However, this effect is largely known to be dependent on the frequency of ultrasound applied.…”

Escherichia coli Wild Type Cells Disruption by Low Intensity Ultrasound for Bacterial Disinfection

“…The samples were collected in sterilised 500 ml Polyethylene bottles in order to avoid any contamination [13]. The samples were stored at ±4°C during the sampling event in the College Mawar Wastewater Treatment Plant UiTM Shah Alam and continuously stored at ±4°C, including the transportation time <0.5 h, until processing in the lab, within 12 h [14,15].…”