Ultrasound processing of liquid system(s) and its antimicrobial mechanism of action

Abstract

Ultrasound creates cavitation phenomena, resulting in the formation of several free radicals, namely OH˙ and H˙, due to the breakdown of the H2O molecule. These radicals affect the cellular integrity of the bacteria, causing the inactivation of several processes, and thus it is important to unravel the mechanism of action of this technology. This research looks into the application and mechanism of action of ultrasound technology as a means of disinfection by acoustic cavitation. Sterile water and synthetic waste water were inoculated with different mutants of Escherichia coli K12 strains containing deletions in genes affecting specific functional properties of E. coli. These were: dnak soxR, soxS, oxyR, rpoS, gadA/gadB, gadC and yneL. Escherichia coli K-12 DoxyR appeared to be more resistant to the treatment together with gadW, gadX, gabT and gabD, whereas the mutant K-12 DdnaK was more sensitive with c. 2.5 log (CFU per ml) reduction in comparison to their isogenic wildtype E. coli K-12. This indicates that the dnaK gene participates in general stress response and more specifically to hyperosmotic stress. The other E. coli deleted genes tested (soxS, rpoS, gadB, gadC, yneL) did not appear to be involved in protection of microbial cells against ultrasound.