[DBS seminar series] "Understanding bacterial inactivation with cavitation at the single cell level"

by Dr Žiga Pandur (Faculty of Mechanical Engineering)

Thursday 14 Dec 2023, 14:00 → 15:30 Europe/Ljubljana

Seminar room of physics (106) (IJS)

Cavitation, a sudden decrease in pressure that triggers the formation of vapor and gas bubbles in a liquid medium, can cause many important industrial problems, such as material loss, noise and vibrations in hydraulic machinery. On the other hand, due to the extreme conditions during growth and collapse of vapor bubbles, cavitation can be a potentially useful phenomenon. for surface cleaning, chemical enhancement and wastewater treatment (i.e. bacterial eradication and virus inactivation). Despite extensive research in recent years, there is still a large gap between understanding the mechanisms that contribute to the effects of cavitation and its application. Although engineers have already commercialized devices that use cavitation, we are still not able to answer the fundamental questions, such as how bubbles increase chemical activity disinfect, clean, and how they affect bacterial cells.

In this work we have investigated the effects of cavitation on simple cell model systems–and compared it with other known chemical, physical and mechanical stress factors. We showed that the fragile but compliant structure of the lipid bilayer is effectively destroyed by acoustic or hydrodynamic cavitation. We have investigated how different modifications of the cell wall of Gram-negative bacteria (Escherichia coli) affect cell stability during sonication and found that peptidoglycan layer modifications significantly increase susceptibility to sonolysis. To investigate the interaction between individual cavitation bubble and bacterial cell, we have developed a new method to generate single micrometer size cavitation bubble. The combination of optical tweezers and high-voltage discharge allowed us to generate cavitation microbubbles precisely in space and time. At the center of the imploding microbubble, the cells get detached, followed by the area of damaged cells. The results indicate that only the cells in the immediate vicinity of the collapsing bubble were affected. The numerical model of bubble collapse allowed us to determine the threshold values of hydrodynamic forces and wall shear stress for cell detachment and cell death.

Quantifying mechanical stability response of bacteria to high-frequency perturbations reveals the mechanisms behind the cleaning effects of cavitation, and also provides a unique tool to characterize the high-frequency mechanical stress response of different biological materials. Our work contributes to a better understanding of the effects of cavitation on bacterial cells and promotes further development of cavitation applications to remove or eradicate bacteria.

Abstract_Žiga Pandur 2023.docx

flyer_ziga_pandur.pdf