Blue/violet laser inactivates methicillin-resistant Staphylococcus aureus by altering its transmembrane potential

Abstract

The resistance of methicillin-resistant Staphylococcus aureus to antibiotics presents serious clinical problems that prompted the need for finding alternative or combination therapies. One such therapy is irradiation with blue light. To determine the alterations in metabolic processes implicated in the observed antimicrobial effects of blue light, we investigated the changes in membrane potential and the presence of free-radical-producing photo-acceptor molecules. Bacterial cultures irradiated with one or two doses of 405nm laser light (each consisting of 121J/cm) were imaged with spectrally resolved laser-scanning microscopes to detect endogenous fluorescent species as well as the voltage sensitive dye 3,3'-Diethyloxacarbocyanine iodide. The endogenous fluorescence indicated the presence of photosensitizers (i.e., porphyrins, NADH, FAD) in the cells, while the exogenous signal allowed us to monitor rapid changes in transmembrane potential following treatment with light. The changes were drastic within the first 5min after irradiation with the first dose and continued slowly after the second irradiation. These results suggest that the early antimicrobial activity of blue light results from alteration of membrane integrity with a consequent decrease in membrane polarization and rapid alteration of vital cellular functions. The observation of an early antimicrobial activity of light is very encouraging, as it suggests that treatment does not necessarily have to be administered over a long period of time.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

“…The emission peaks in the chromatograms indicate the presence of endogenous porphyrins. Similar studies from other investigators suggested the presence of both porphyrins and flavins in A. actinomycetemcomitans (Cieplik et al, 2014; Fyrestam et al, 2015), porphyrins, flavin adenine dinucleotide (FAD), and nicotinamide adenine dinucleotide (NADH) in MRSA (Biener et al, 2017), porphyrins in P. gingivalis ( Fyrestam et al, 2015; Yoshida et al, 2017), porphyrins in S. cerevisiae (Fyrestam et al, 2015), and porphyrins (a mixture of coproporphyrin I, coproporphyrin III, and PpIX) in Helicobacter pylori (Battisti et al, 2017a; Battisti et al, 2017b) according to the spectroscopic or chromatographic analyses. Some other studies provided the evidence that the cytotoxicity of aBL to microbes is mediated by the aBL-induced production of ROS (Cieplik et al, 2014; Galbis-Martinez et al, 2012; O’Donoghue et al, 2016; Ramakrishnan et al, 2016; Yoshida et al, 2017).…”

“…Increased nucleic acid release was also observed from the measurement of spectrophotometer, with up to 50 % increase in DNA concentration into the extracellular media in the case of both microbes. The above results are endorsed by the work of Biener et al, in which the authors suggested that the inactivation of bacteria by using aBL is due to the aBL-induced marked changes in the transmembrane potential, such as alterations in membrane integrity or disabling ion pumps that made the membrane more permeable to ions (Biener et al, 2017). …”

“…Evidences were reported that aBL inactivation of microbes was attributed to ROS-induced cell membrane damage (Biener et al, 2017; McKenzie et al, 2016), inactivation of virulence factors (Fila et al, 2016), DNA-oxidation (Kim and Yuk, 2017; Yoshida et al, 2017), genetic changes (Adair and Drum, 2016; Kim and Yuk, 2017; Yang et al, 2017), etc. However, some other studies showed that only slight damage to membrane integrity after aBL inactivation (Kim and Yuk, 2017).…”

“…Biener et al demonstrated in their work that two applications of aBL were more effective in inactivating MRSA than a single application with the equivalent exposure (Biener et al, 2017). Two groups of MRSA cultures on agar plates were exposed to a single exposure of 405-nm aBL at 121 J/cm 2 and to two exposures of aBL from the same light source at 60.5 J/cm 2 for each exposure with 30 min between, and approximately 1.05- and 1.71-log 10 inactivation of MRSA CFU were observed, respectively.…”

Healing Effects of Photobiomodulation on Diabetic Wounds

“…These phorphyrins absorb the photon energy, become excited, and jump to the triplet state. They then release the extra energy and pass it onto molecular oxygen creating ROS, which interact with numerous macromolecules within the cell causing cellular damage and leading to cell death [38].…”