Inactivation of microorganisms by low-frequency high-power ultrasound: 1. Effect of growth phase and capsule properties of the bacteria

Gao, Shengpu; Lewis, Gillian; Ashokkumar, Muthupandian; Hémar, Yacine

doi:10.1016/j.ultsonch.2013.06.006

Cited by 196 publications

(118 citation statements)

References 60 publications

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“…Our findings and those of Al Bsoul et al might be due to various effects on the medium through which these mechanisms offset each other. We also observed that the Gram-negative bacterium E. coli was more sensitive to ultrasound treatment than the Gram-positive bacterium S. aureus (Table 1), a finding that was in accordance with previously published studies (37)(38)(39)(40). According to the literature, this result might be due to the thicker and more tightly adherent layer of peptidoglycan in Gram-positive cells (41).…”

Section: Enumeration Of Surviving Cells By Plate Counts (Cultivability)supporting

confidence: 92%

Evaluation of Ultrasound-Induced Damage to Escherichia coli and Staphylococcus aureus by Flow Cytometry and Transmission Electron Microscopy

Ahn

Liu

et al. 2016

Appl Environ Microbiol

148

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bAs a nonthermal sterilization technique, ultrasound has attracted great interest in the field of food preservation. In this study, flow cytometry and transmission electron microscopy were employed to investigate ultrasound-induced damage to Escherichia coli and Staphylococcus aureus. For flow cytometry studies, single staining with propidium iodide (PI) or carboxyfluorescein diacetate (cFDA) revealed that ultrasound treatment caused cell death by compromising membrane integrity, inactivating intracellular esterases, and inhibiting metabolic performance. The results showed that ultrasound damage was independent of initial bacterial concentrations, while the mechanism of cellular damage differed according to the bacterial species. For the Gram-negative bacterium E. coli, ultrasound worked first on the outer membrane rather than the cytoplasmic membrane. Based on the double-staining results, we inferred that ultrasound treatment might be an all-or-nothing process: cells ruptured and disintegrated by ultrasound cannot be revived, which can be considered an advantage of ultrasound over other nonthermal techniques. Transmission electron microscopy studies revealed that the mechanism of ultrasound-induced damage was multitarget inactivation, involving the cell wall, cytoplasmic membrane, and inner structure. Understanding of the irreversible antibacterial action of ultrasound has great significance for its further utilization in the food industry. With increasing demands for safe, nutritious, and minimally processed products, ultrasound has attracted great interest as an alternative nonthermal technology for microbial inactivation in food preservation (1, 2). Since the 1960s, many studies have been conducted to investigate the bactericidal effects and mechanisms of ultrasound (3-5). At present, acoustic cavitation is most widely accepted as the mechanism of sterilization by highpower ultrasound (frequencies between 18 kHz and 100 kHz). The formation, growth, and collapse of cavitation bubbles in liquid media cause mechanical effects (microstreaming, high shear force, shock waves) and sonochemical reactions (free radicals, hydrogen peroxide), eventually resulting in the impairment or disruption of bacterial cells (6-8). The inhibitory effects of ultrasound on microbial cells are multifactorial, including pore formation, cell wall thinning, cell membrane disruption, release of cytoplasm contents, and damage to DNA structure (9, 10). However, there is still no consensus about the primary effect of ultrasound that causes cell death. Most researchers have argued that the primary target of ultrasound is the cytoplasmic membrane, which consists of lipoprotein layers (11, 12). Ananta et al., on the other hand, suggested that ultrasound-induced cell death might not be related to cytoplasmic membrane damage (13).There have been numerous studies on the antimicrobial efficacy of ultrasound in the food industry, which have been reviewed by Awad et al. Unfortunately, in order to determine the impact of ultrasound treatment, most of...

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Section: Enumeration Of Surviving Cells By Plate Counts (Cultivability)supporting

confidence: 92%

Evaluation of Ultrasound-Induced Damage to Escherichia coli and Staphylococcus aureus by Flow Cytometry and Transmission Electron Microscopy

Ahn

Liu

et al. 2016

Appl Environ Microbiol

148

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“…Gao et al have confirmed that the inactivation of microorganisms is due to shear forces generated by collapse of cavitation bubbles [39,40]. Given this background and our own experimental results, we consider that physical effects are responsible for algae disruption under ultrasonication in the present study.…”

Section: Physical Effectsmentioning

confidence: 59%

Effect of sonication frequency on the disruption of algae

Kurokawa

King

et al. 2016

Ultrasonics Sonochemistry

105

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In this study, the efficiency of ultrasonic disruption of Chaetoceros gracilis, Chaetoceros calcitrans, and Nannochloropsis sp. was investigated by applying ultrasonic waves of 0.02, 0.4, 1.0, 2.2, 3.3, and 4.3 MHz to algal suspensions. The results showed that reduction in the number of algae was frequency dependent and that the highest efficiency was achieved at 2.2, 3.3, and 4.3 MHz for C. gracilis, C. calcitrans, and Nannochloropsis sp., respectively. A review of the literature suggested that cavitation, rather than direct effects of ultrasonication, are required for ultrasonic algae disruption, and that chemical effects are likely not the main mechanism for algal cell disruption. The mechanical resonance frequencies estimated by a shell model, taking into account elastic properties, demonstrated that suitable disruption frequencies for each alga were associated with the cell's mechanical properties. Taken together, we consider here that physical effects of ultrasonication were responsible for algae disruption. HighlightsThe disruption of algae is frequency dependent and algae specific.The resonance frequencies of algae are calculated using elastic modulus measures.Cavitation bubbles are necessary for the algae disruption process.Chemical effects are not the main mechanism for algal cell disruption.Suitable disruption frequencies are associated with the cell's mechanical properties.

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“…It has been observed that ultrasound was more effective in destroying the gram negative bacteria (Enterobacter aerogenes) than gram positive bacteria (Staphylococcus spp). The latter is not much affected due to the resistance from the capsules [12]. The use of ultrasound by itself may not be effective in destroying all the microbes in food.…”

Section: Discussionmentioning

confidence: 99%

Thermosonication as an Upcoming Technology in the Dairy Industry: An Overview

Ghosh¹

2017

J Adv Dairy Res

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Ultrasound waves are longitudinal sound waves of frequency of 20 kHz or more. As low amplitude ultrasonic waves do not significantly modify the material under examination, they can be used to analyse the material. However, high amplitude ultrasonic waves can be used to process food as they have the capacity to alter the food material by cavitation. Nowadays ultrasound processing is increasingly being used in the dairy industry. The use of high amplitude ultrasound by itself may not be effective in in bringing about the desired processing effects. Hence, it can be coupled with pressure or heat or both to get the desired results. Thermosonication involves the simultaneous use of low frequency ultrasound waves (20 kHz) along with heat; and the both together have some synergistic effect. When heat and ultrasound is used together, the process temperature is considerably reduced compared to the conventional heating process, making it a green and economical technology as less energy is consumed; this in turn makes it a cost-efficient process. If thermosonication is seen to bring about the desired effects in milk, then it can be used as a commercial method to treat and homogenize milk in the future.

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Inactivation of microorganisms by low-frequency high-power ultrasound: 1. Effect of growth phase and capsule properties of the bacteria

Cited by 196 publications

References 60 publications

Evaluation of Ultrasound-Induced Damage to Escherichia coli and Staphylococcus aureus by Flow Cytometry and Transmission Electron Microscopy

Evaluation of Ultrasound-Induced Damage to Escherichia coli and Staphylococcus aureus by Flow Cytometry and Transmission Electron Microscopy

Effect of sonication frequency on the disruption of algae

Thermosonication as an Upcoming Technology in the Dairy Industry: An Overview

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