Infrared laser effects at fluences used for treatment of dentin hypersensitivity on DNA repair in Escherichia coli and plasmids

Low-intensity infrared lasers are proposed in clinical protocols based on biostimulative effects, yet dosimetry is inaccurate and their effects on DNA at therapeutic doses are controversial. The aim of this work was to evaluate the effects of low-intensity infrared laser on survival and induction of filamentation of Escherichia coli cells, and induction of DNA lesions in bacterial plasmids. E. coli cultures were exposed to laser (808 nm, 100 mW, 40 and 60 J/cm2) to study bacterial survival and filamentation. Also, bacterial plasmids were exposed to laser to study DNA lesions by electrophoretic profile and action of DNA repair enzymes. Data indicate low-intensity infrared laser has no effect on survival of E. coli wild type and exonuclease III, but decreases the survival of formamidopyrimidine DNA glycosylase/MutM protein and endonuclease III deficient cells in stationary growth phase, induces bacterial filamentation, does not alter the electrophoretic profile of plasmids in agarose gels and does not alter the electrophoretic profile of plasmids incubated with endonuclease III, formamidopyrimidine DNA glycosylase/MutM protein and exonuclease III. Our findings show that low-intensity laser exposure causes DNA lesions at sub-lethal level and induces cellular mechanisms involved in repair of oxidative lesions in DNA. Studies about laser dosimetry and safety strategies are necessary for professionals and patients exposed to low-intensity lasers at therapeutic doses.