Cavitation in the environment is the main reason for the destructive effect of ultrasound on microorganisms. If the formation of bubbles was suppressed by increasing the external pressure, then the destructive effect on protozoa decreased. The almost instantaneous rupture of objects in the ultrasound field was caused by air bubbles or carbon dioxide in plant cells trapped inside these organisms.
This shows that large pressure differences arising during cavitation lead to rupture of cell membranes and whole small organisms. The effect of ultrasound on various types of fungi has been studied many times. So, ultrasound is successfully used in phytopathology. On sugar beet seeds infected naturally with Phoma betae, Cercospora beticola, Alternaria sp. or Fusarium sp., it was possible to destroy these fungi and bacteria much better by short-term irradiation with ultrasound in water than it has been possible to do with etching. Irradiation of seeds with ultrasound during etching significantly enhances the effect of a fungicidal or bactericidal substance. The reason, apparently, is that sound vibrations increase the rate of diffusion of water and substances dissolved in it through the membranes of plant cells,which achieves a faster action on fungi and bacteria.
Ultrasound also has a negative effect on individual cells of higher organisms. When irradiating red blood cells (erythrocytes), the following was observed: they lost their original shape and stretched; in this case, their discoloration occurred (as a result of hemolysis). With further irradiation, they finally burst and disintegrated into many separate small balls.
Already in 1928, it was established that luminous bacteria are destroyed by ultrasound. In subsequent years, a large number of works were published on the effect of ultrasonic waves on bacteria and viruses. At the same time, it turned out that the results could be very diverse: on the one hand, there was an increased agglutination, loss of virulence or complete death of bacteria, on the other hand, the opposite effect was also noted - an increase in the number of viable individuals. The latter occurs especially often after short-term irradiation and can be explained by the fact that during short-term irradiation, first of all, mechanical separation of accumulations of bacterial cells occurs, due to which each individual cell gives rise to a new colony.
It was found that typhoid rods are completely killed by ultrasound with a frequency of 4.6 MHz, while staphylococci and streptococci are damaged only partially. When bacteria die, their dissolution occurs simultaneously, i.e., the destruction of morphological structures, so that after the action of ultrasound, not only the number of colonies in a given culture decreases, but the counting of the number of individuals reveals a decrease in the morphologically preserved forms of bacteria. When irradiated with ultrasound at a frequency of 960 kHz, bacteria with a size of 20–75 µm are destroyed much faster and more completely than bacteria with a size of 8–12 µm [23].
At the Moscow Central Scientific Research Institute of Traumatology and Orthopedics named after V. I. NN Priorov conducted research [24] on the effect of low-frequency ultrasonic cavitation on the vital activity of various strains of staphylococcus. In experiments in vitro, the following results were obtained. The sonication was carried out at a temperature of 32 ° C using an ultrasonic disintegrator from MSE (Great Britain) with the following technical parameters: power 150 W, vibration frequency 20 kHz, amplitude 55 μm. The exposure time was 1, 2, 5 "7, 10 minutes. For each exposure, separate vials with 5 ml of microorganism suspension containing 2500 microbial bodies in 1 ml of liquid were used. The research results showed thatthat the ability of microorganisms to multiply when sowing them on solid nutrient media immediately after ultrasonic treatment is not only not weakened, but with some sonication exposures (1-3 min) it even slightly increases. At the same time, when staphylococcus was sonicated for 5, 7, and 10 minutes, the changes in the number of grown colonies on the agar surface in Petri dishes were insignificant and almost did not differ from the control. The effect of ultrasound on microorganisms may appear not immediately, but after a while, necessary for the development of metabolic disorders in the cells, therefore, the inoculation of staphylococcus on solid nutrient media was studied 24, 36, and 48 hours after ultrasonic treatment. Before plating on Petri dishes, the sonicated staphylococcus strains were cultured in test tubes with broth in a thermostat at 37 ° C. Was found,that in 24 and 36 hours after ultrasonic treatment, the number of grown colonies of staphylococci in comparison with the control decreases, the seeding rate of staphylococcus is inversely proportional to the time of sounding of microorganisms. After 7-10 minutes of sonication, the seeding either did not give any growth, or single colonies not typical for staphylococcus grew on Petri dishes. After 48 hours, the inhibitory effect of ultrasound was more pronounced and manifested itself in a further decrease in the seeding of microorganisms at all exposures. After 7-10 minutes of sonication, the seeding either did not give any growth, or single colonies not typical for staphylococcus grew on Petri dishes. After 48 hours, the inhibitory effect of ultrasound was more pronounced and manifested itself in a further decrease in the seeding of microorganisms at all exposures. After 7-10 minutes of sonication, the seeding either did not give any growth, or single colonies not typical for staphylococcus grew on Petri dishes. After 48 hours, the inhibitory effect of ultrasound was more pronounced and manifested itself in a further decrease in the seeding of microorganisms at all exposures.
A study of the sensitivity of sounded microorganisms to the action of certain antibiotics and antiseptics showed that in 8 out of 13 drugs used, the minimum inhibitory concentration after ultrasonic treatment of staphylococcus decreased 2-4 times. This indicates the advisability of the combined use of low-frequency ultrasonic vibrations and antibacterial solutions for a more effective impact on the microbial cell [7, 10].
The destructive effect of ultrasonic waves depends on the concentration of the bacterial suspension. In a too thick and, therefore, very viscous suspension, no destruction of bacteria is observed, but only heating can be noted. Different strains of the same bacterial species may have completely different attitudes towards ultrasound irradiation [11].
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Thus, we can conclude that the effect of ultrasound on biomaterial in general and microorganisms, in particular, depends on many environmental factors and on the state of living matter, and in reality it is rather difficult to predict.
Experiments on ultrasonic cleaning of titanium intraosseous dental implants in various working solutions were carried out at the department of SSTU.
Cleaning of products is the more efficient, the closer they are to the emitting surface of the emitter. With distance from the emitter, the intensity of ultrasonic vibrations changes along an idealized curve. The best result was obtained at an intensity of 16 W / cm2 in tap and industrial water at 50 + 5 ° C with a sulfanol concentration of 0.25% with a sonication time of 5-10 minutes (Fig. 2.1). The sonicated products were at a distance of no more than 10 mm from the radiating surface.
Figure: 2.1. Graph of the dependence of the contamination of products on the sounding time at an vibration intensity of 16 W / cm2
Thus, according to the experiments, an increase in intensity from 0.4 to 16 W / cm2 gives an improvement in the quality of cleaning (Fig. 2.2), but 100% sterilization of products is not achieved in any mode.
Figure: 2.2. A graph of the dependence of the sterilizing effect of ultrasound on the intensity of ultrasound.
