Effects of a pulsed light‐induced stress on E nterococcus faecalis

Aims Pulsed light ( PL ) technology is a surface decontamination process that can be used on food, packaging or water. PL efficiency may be limited by its low degree of penetration or because of a shadow effect. In these cases, surviving bacteria will be able to perceive PL as a stress. Such a stress was mimicked using low transmitted energy conditions, and its effects were investigated on the highly environmental adaptable bacterium E nterococcus faecalis V 583. Methods and Results In these laboratory conditions, a complete decontamination of the artificially inoculated medium was performed using energy doses as low as 1·8 J cm −2 , while a treatment of 0·5, 1 and 1·2 J cm −2 led to a 2·2, 6 and 7‐log 10  CFU ml −1 reduction in the initial bacterial population, respectively. Application of a 0·5 J cm −2 pretreatment allowed the bacteria to resist more efficiently a 1·2 J cm −2 subsequent PL dose. This 0·5 J cm −2 treatment increased the bacterial mutation frequency and affected the abundance of 19 proteins as revealed by a global proteome analysis. Conclusions E nterococcus faecalis is able to adapt to a PL treatment, providing a molecular response to low‐energy PL dose, leading to enhanced resistance to a subsequent treatment and increasing the mutation frequency. Significance and Impact of the Study This study gives further insights on E nt. faecalis capacities to adapt and to resist to stress.