The relationship between inactivation and morphological damage of Salmonella enterica treated by high hydrostatic pressure

- HHP can be applied to inactivate S. enterica.
- HHP can induce morphological changes in internal and external structures of bacterial cell.
- Observations of S. enterica cell morphological damage by TEM and SEM.
- HHP also causes membrane protein degradation by SDS-PAGE analysis.

The effects of high hydrostatic pressure (HHP) treatments on Salmonella enterica cells were investigated using viability counting, scanning and transmission electron microscopy, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), in order to determine the optimal inactivation conditions and to further understand the mechanisms underlying the inactivation of microorganisms under HHP. The results showed that 350-MPa treatment for 5 min could considerably inactivate S. enterica, with increased uptake of propidium iodide (PI) and the number of viable bacteria decreasing from 109 CFU/mL to no viable bacteria. Damage to the cell wall, cell membrane, and cytoplasmic components by HHP treatments was observed on scanning and transmission electron microscopy images. The SDS-PAGE results showed that the protein bands differed between HHP-untreated and HHP-treated S. enterica, in that HHP decreased the protein content and caused partial protein degradation. Therefore, our results indicate that HHP can be used to inactivate S. enterica, via morphological changes in the internal and external cellular structures, as well as through membrane damage, cell wall rupture, and membrane protein degradation.