The antibacterial mechanism of ultrasound in combination with sodium hypochlorite in the control of Escherichia coli

In the present study, the action mechanism of ultrasound (US) combined with sodium hypochlorite (SH) against Escherichia coli was illustrated by different analysis, including reduction, particle size distribution, scanning electron microscopy (SEM), transmission electron microscopy (TEM), K+ leakage, confocal laser scanning microscopy (CLSM) and fluorescence spectroscopy of Escherichia coli. The results showed that ultrasound improved the antimicrobial effect of SH in control of E. coli. No significant difference was obtained in reduction of E. coli, CLSM analysis and K+ leakage between US + SH30 (US + 30 ppm SH) and SH50 (50 ppm SH) treatment. Smaller particle size was recorded in US and US + SH30 treatment. The changes of morphology and intracellular organization of E. coli cells as a result of these treatments were confirmed by SEM and TEM analyses. Fluorescence spectroscopy results indicated SH30, US + SH30 and SH50 treatment caused the burial of tyrosine residues and tryptophan residues as well as increase of hydrophobicity. Therefore, the mechanism of US + SH30 treatment against E. coli involved decreased particle size, damaged membrane and changes of intracellular organization and protein conformation.