Abstract
Semiconductor laser devices are readily available and practical radiation sources providing wavelength tenability and high monochromaticity. Low-intensity red and near-infrared lasers are considered safe for use in clinical applications. However, adverse effects can occur via free radical generation, and the biological effects of these lasers from unusually high fluences or high doses have not yet been evaluated. Here, we evaluated the survival, filamentation induction and morphology of Escherichia coli cells deficient in repair of oxidative DNA lesions when exposed to low-intensity red and infrared lasers at unusually high fluences. Cultures of wild-type (AB1157), endonuclease III-deficient (JW1625-1), and endonuclease IV-deficient (JW2146-1) E. coli, in exponential and stationary growth phases, were exposed to red and infrared lasers (0, 250, 500, and 1000 J/cm2) to evaluate their survival rates, filamentation phenotype induction and cell morphologies. The results showed that low-intensity red and infrared lasers at high fluences are lethal, induce a filamentation phenotype, and alter the morphology of the E. coli cells. Low-intensity red and infrared lasers have potential to induce adverse effects on cells, whether used at unusually high fluences, or at high doses. Hence, there is a need to reinforce the importance of accurate dosimetry in therapeutic protocols.
Highlights
Low-intensity lasers are lightweight, available sources of monochromatic non-ionizing radiation [1]
The results showed that low-intensity red and infrared lasers at high fluences are lethal, induce a filamentation phenotype, and alter the morphology of the E. coli cells
The survival rates of stationary cultures of the same E. coli strains were evaluated to verify whether the lowintensity red and infrared laser effects are dependent on the physiological conditions of the cells (Table 3)
Summary
Low-intensity lasers are lightweight, available sources of monochromatic non-ionizing radiation [1]. After absorption of laser radiation energy at low fluences by such photoacceptors, transduction processes are responsible for activating intracellular signaling pathways, thereby amplifying the primary photosignal [4]. It is possible that photobiological side-effects occur when the antioxidant systems are not capable of protecting the cells against free radical attack. This situation can occur when antioxidant systems are not functioning, or when inadequate exposure to low-intensity lasers at high doses arises. An intracellular imbalance between oxidant and antioxidant contents means that free radicals might occur in cells exposed to low-intensity lasers when high doses are used. Sub-lethal DNA damage has been reported after exposure to lowintensity red and infrared lasers in eukaryotic [5,6,7] and prokaryotic cells [8,9]
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