Morphological Effects of Pulse Ultraviolet Light and Anolyte Treatment on Bacterial Cell Wall

Introduction: Pulse ultraviolet light (PUV) is effective to inactivate bacterial contaminated surfaces. Anolyte, the product of passing an electric current through a solution of sodium chloride, is currently being used in the food industry as a sanitizer and is equipment and environment friendly. There is little information about the cellular damage when the PUV treatment is combined with an anolyte wash.

Purpose: In this study PUV for 15 and 30 s, an anolyte wash with a 300 ppm residual chlorine for 3 min and a PUV treatment followed by the anolyte wash was used to determine the morphological effect on Salmonella, Listeria monocytogenes (LM) and Staphylococcus aureus (SA) cells suspended in buffer peptone water. Following the PUV treatment, the cells were harvested and fixed for TEM examination.

Methods: After the anolyte wash and PUV treatment/anolyte wash the anolyte was inactivated before harvesting and fixing for TEM examination.

Results: The TEM images showed disruption of the Salmonella’s outer cell membrane with some cytoplasm leakage after both the PUV and anolyte wash.  Increased cell wall damage and cytoplasm leakage was observed for the PUV/anolyte treated Salmonella cells. The LM and SA outer cell membrane showed less damage with no cytoplasm leakage after the PUV or anolyte treatment, but increased cell wall damage did occur after the combined treatment of PUV followed by the anolyte wash. 

Significance: These results indicate that the gram negative bacteria are more sensitive to the PUV and anolyte treatments than the gram positives.  However, the hurdle treatment (PUV followed by anolyte wash) is an effective way to inactivate the bacteria pathogens.