Low-frequency ultrasound bactericidal capacity study in intermittent ultrasonication process

The low-frequency ultrasound (f = 26.5 kHz) was found to have a bactericidal effect upon the main representatives of bacterial flora: Staphylococcus, Proteus, E-coli and Pseudomanas aeruginosa. However, ultrasound suppresses bacterial flora during a comparatively long ultrasonication time ranging from 18 to 27 min. It was found that the determinant factor ensuring the bactericidal effect of low-frequency ultrasound is cavitation. To reduce the required ultrasonication time, while maintaining the high bactericidal effect, Bauman Moscow State Technical University (BMSTU) has developed a new ultrasonic treatment method designed for infected wounds and patented in the RF [8]. When implementing this method, it is proposed to intensify the cavitational effect of ultrasound through complementary physical and chemical factors: low-concentration antiseptic agents, excessive external static pressure, and optimum temperature of ultrasonicated solution. The proposed intensification of ultrasonic effect was found to reduce the sterilization time of bacterial suspensions from 5 to 7.2 times, while keeping the maximum required ultrasonication time within 5 min. The article considers further potential reduction of cavitational exposure time for tissues on the basis of earlier found aftereffect of ultrasound. This aftereffect means that a pre-sonicated solution has higher bactericidal properties than non-sonicated solutions and preserves its bactericidal capacity for specific time [11]. The article demonstrates the efficacy of the continuous ultrasonication process replacement by the intermittent process, which follows the cycle: ultrasonication – pause – ultrasonication. Experiments proved that, with optimum temporal relationship between the periods of ultrasonic exposure and rest, the complete sterilization end-time of bacterial suspensions can be reduced still more by 20…30%. Thus, the proposed intermittent ultrasonication process is an effective instrument of reducing the cavitational exposure of an organism, while maintaining its high bactericidal effect no worse than that of the continuous ultrasonication process. The research findings were successfully tested in the Traumatology department of N.N. Burdenko Main Military Clinical Hospital during the trial of the proposed method for ultrasonic treatment of infected wounds.