Near-infrared LEDS provide persistent and increasing protection against E. faecalis

In a previous study, we have shown that non-coherent light-emitting diodes (LEDs) are able to significantly decrease Enterococcus faecalis viability, in vitro. In particular, the concurrent treatment for 5 min with sodium hypochlorite (NaOCl) 1.0% and LED permitted to obtain the total inactivation of the culture. The primary outcome of this study was to verify if the photoinactivation was only temporary or stable over 1 week. The secondary outcome was to verify if using a minor concentration of NaOCl together with LED irradiation, it was possible to reach the total inactivation of the culture. Bacterial suspensions were subjected to different protocols. NaOCl samples were treated with 0.5% sodium hypochlorite for 5 min; LED 5 were subjected to 880-nm LED irradiation for 5 min and LED+NaOCl were contemporary subjected to LED irradiation and 0.5% sodium hypochlorite for 5 min. Then the colony forming units per milliliter (CFU/mL) were analyzed and recorded at 5 min, 24 h, 48 h and 1 week. The data were submitted to ANOVA and LSD post hoc tests at a level of significance of 0.05. Live dead assay and fluorescent microscope observations were also performed for all group at all timing points. The results showed that the 3 protocol treatments were able to decrease significantly the bacterial count respect controls, however, after 5 min, 24 h and 48 h the most effective reduction was measured for NaOCl and NaOCl+LED 5. In the first 48 h LED 5 alone reduced significantly the bacterial count respect controls, but it was higher respect the other tested groups. On the contrary, after 1 week we found an interesting result: samples treated with LED were characterized by a decrement of bacterial count, independently from the addition of sodium hypochlorite. Samples treated with NaOCl alone were characterized by a mild increment of bacterial count, although results were still significant respect C+. The secondary outcome was not confirmed: a concentration of NaOCl 0.5% together with LED irradiation did not permit to reach the total inactivation of the culture.