Assessing the effect of different ultrasonic frequencies on bacterial viability using flow cytometry

Abstract

Aims: This research investigated the effect of sonication at frequencies of 20, 40 and 580 kHz and approximately the same acoustic intensity on the viability and declumping of two micro‐organisms (Escherichia coli and Klebsiella pneumonia). Methods and Results: Two analytical methods were employed; viable plate counts (CFU ml−1) and flow cytometry to identify and quantify both live/viable and dead bacteria in the bulk liquid. Flow cytometry results for E. coli and Kl. pneumonia indicated a high sensitivity to 20 and 40 kHz frequency with a continuous decrease in the viable cells and an increase in dead cells during experiments. In contrast, results using the higher frequency of 580 kHz indicate predominantly deagglomeration of bacterial clumps rather than cell membrane disruption (Joyce et al. 2003). Results indicate a good correlation between flow cytometry and viable plate count methodology. Conclusions: Sonication has two different effects on bacteria (i) inactivation and (ii) declumping; however, the scale of these effects is dependent on intensity and frequency. Flow cytometry provides a method to distinguish between and quantify the effects through the observation of two subpopulations: (i) live/viable and (ii) dead bacterial cells. Significance and Impact of the study: Treatment using power ultrasound has been shown to have a significant impact on microbial activity. This is the first time a study has compared the influence of a range of different frequencies, but at similar power settings on the survival of bacteria in phosphate buffer saline (PBS). This work is of importance for applications where ultrasound has been considered for use in industry as a means of disinfection including the treatment and pretreatment of water and also for the sterilization of liquid foods.

Combination of thermal and dual‐frequency sonication processes for optimum microbiological and antioxidant properties in cherry tomato

“…The maximum firmness was observed at 20/40 kHz, 40°C, and 2 min while the minimum value was observed at 20/60 kHz, 60°C, and 6 min. The losses of firmness of fruit during sonication have been reported by various authors and were attributed to tissue rupturing and cell wall degradation which lead to disturbances in the constituents of cell wall such as pectin methylesterase and polygalacturonates (Vicente, Saladié, Rose, & Labavitch, ; Vivek et al, ), and also due to the mechanical effects induced by pressure (Joyce, Al‐Hashimi, & Mason, ).…”

Inactivation of Planktonic Escherichia coli by Focused 2-MHz Ultrasound

“…At still lower power and frequencies of 0.5 – 0.8 MHz, ultrasound exposure did not inactivate the bacteria; coliform counts instead increased, apparently due to disaggregation of clusters by ultrasound exposure (Joyce et al . 2003; 2011). In other cases, the power requirements to achieve modest levels of inactivation can be extreme; e.g ., about 1.5 kW-hrs per liter treated (Drakapoulou et al .…”

Effect of sonication frequency on the disruption of algae

“…Inactivation of microorganisms by ultrasound was first reported in the 1920s [8], and the specific mechanism began to be reported in the 1960s [9]. The inactivation mechanism differs with different parameters, such as temperature, ultrasonic frequency, and acoustic power, and between microorganisms; the inactivation mechanisms for ultrasonic inactivation of Escherichia coli [10], Listeria monocytogenes [11] and Alicyclobacillus acidiphilus [12] have been reported.…”