Effects of a pulsed light-induced stress on Enterococcus 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 Enterococcus faecalis V583. 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: Enterococcus 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 Ent. faecalis capacities to adapt and to resist to stress.

Adaptation of Pseudomonas aeruginosa to a pulsed light-induced stress.

AIMS: Pulsed light (PL) technology is an efficient surface decontamination process. Used in low transmitted energy conditions, PL induces a stress that can be perceived by bacteria. The effect of such a PL stress was investigated on the highly environmental adaptable germ Pseudomonas aeruginosa PAO1. METHODS AND RESULTS: Pulses of transmitted energy (fluence) reaching 1·8Jcm(-2) can kill 10(9) bacteria. Application of a lower sublethal PL dose allowed the bacteria to resist and survive more efficiently to a subsequent dose of PL. This sublethal dose was not increasing the mutation frequency of Ps. aeruginosa, but altered the abundance of 15 proteins as revealed by a global proteome analysis, including stress-induced proteins, phage-related proteins, energy and carbon metabolisms, cell motility, and transcription and translation regulators. CONCLUSIONS: A response to a low-energy PL dose takes place in Ps. aeruginosa, reducing the energy conversion systems, while increasing transcription and translation processes to produce proteins involved in chaperone mechanisms and phage-related proteins, probably to protect the bacterium against a new PL-induced stress. SIGNIFICANCE AND IMPACT OF THE STUDY: Taken together, these results suggest that a low-energy PL dose is sufficient to provoke adaptation of Ps. aeruginosa, leading to enhancing its resistance to a subsequent lethal treatment.