Bacterial inactivation by infrared lasers

Abstract Infrared radiation is the most easily non-ionizing radiation found in nature and is used in healthcare areas to promote biological effects. Lasers are artificial infrared radiation sources that, for biomedical applications, are classified as low-, medium- and high-power lasers according to the power output. There are many beneficial bacteria in the body. However, bacteria also cause infectious processes in local biological tissues and systemic infections, which are responsible for many deaths worldwide, mainly those that are multi-drug resistant. Lasers have been proposed to inactivate bacteria, and such an approach can be efficient against non- and multi-drug-resistant bacteria since the mechanisms involved in laser-induced bacterial inactivation do not cause resistance. This review summarizes studies on bacterial inactivation by low-, medium- and high-power infrared lasers. Studies were accessed via MEDLINE/Pubmed and Google Scholar using headings and keywords, and those on effects induced by infrared lasers on bacteria were cited in the accessed studies. Results from these studies suggest that low-, medium- and high-power infrared lasers can be effective for bacterial inactivation by photochemical and photothermal mechanisms. The photochemical mechanism could be involved in bacterial inactivation caused by low- and medium-power infrared lasers and by those high-power infrared lasers at the lowest fluences or energies, and the photothermal mechanism could be involved in bacterial inactivation caused by high-power infrared lasers at the highest fluences or energies.