Different Aspects of Using Ultrasound to Combat Microorganisms

Abstract

Growing resistance of microorganisms to antibiotics due to their widespread use has led to multiple bacterial infections posing a serious threat to health and human life. Low-frequency ultrasound is one of physical methods for inactivation of pathogenic microbial cells. Application of ultrasound is safe, demonstrates good tissue penetration without significant attenuation of energy, and does not induce microbial resistance. Bactericidal effect of ultrasound is based on acoustic cavitation-the growth and collapse of microbubbles in a liquid medium, resulting in shock waves, shear forces, and microjets which cause irreversible damage and inactivation of microorganisms. The present review combines and analyzes literature data on in vitro and in vivo studies and summarizes works demonstrating the ability of ultrasound, alone or in combination with other methods, to combat pathogenic microorganisms. The results of various studies presented in this review show that low-frequency ultrasound has a noticeable antimicrobial effect on planktonic cells of microorganisms and biofilms. Ultrasound synergistically enhances the effectiveness of other antibacterial agents and activates molecules called sonosensitizers, resulting in the formation of compounds toxic to microbial cells. Ultrasound can also promote local release of antimicrobial drugs from liposomes, as well as from medical implants.

Antimicrobial Effect of Phytochemicals from Edible Plants

“…Conventional methods of microbial inactivation and food decontamination include thermal processing, sanitization, water washing, drying, freezing, refrigeration, irradiation, modified atmosphere packaging (MAP), and the addition of antimicrobial agents, disinfectants, or salts. Irradiation, heat, high pressure, magnetic or electrical fields, and ultrasound are microbial inactivation methods that do not induce microbial resistance [16,57,294,295]. Water washing and sanitization reduce bacterial load with limited success, and disinfectants might cause genotoxicity and carcinogenicity.…”

“…Moreover, US may promote more uniform dispersion of a sensitizer in the growth medium. Generally, US is the transmittance of physical pressure (in longitudinal and transverse waves) through a medium at frequencies of more than 20 kHz, which is above the human hearing range [16,314]. US is already extensively applied in medicine and biology; it is now reaching the field of waterborne and foodborne disease prevention.…”

“…The factors that affect the efficacy of US on microbial decontamination are the US amplitude, exposure duration, treatment temperature, traits of the food, and the volume being processed [16,[314][315][316]. In a recent study by , the influence of US on 50 and 100 µM curcumin-mediated PDT treated by blue light (70 J cm −2 ) against E. coli and S. aureus in freshly squeezed orange juice was investigated and analyzed [183].…”

“…The main hypothesis suggests that the energy release is due to the collapsing microbubbles, which lead to the sonolysis of water and/or sensitizer molecules. In this way, the resulting radicals react with oxygen to form ROS [16]. As in the case of classical photodynamic therapy, sonoluminescence may cause either the type I process, leading to the formation of secondary radicals, or the type II process, in which mainly singlet oxygen eradicates the pathogenic cells.…”

“…The use of photodynamic therapy presents a promising possibility to improve the antimicrobial activity of phytochemicals, since many of them are photosensitizers (PSs). Although many aspects of PSs were covered by numerous reviews [11][12][13][14][15][16], edible plants and their PSs were not seriously considered as sources of new drugs and preservatives. They in fact deserve special attention, because actively cultivated edible plants are already available which are rich in useful phytochemicals.…”