title: The effects of 405 nm light on bacterial membrane integrity determined by salt and bile tolerance assays, leakage of UV-absorbing material and SYTOX green labelling.
abstract: Bacterial inactivation by 405 nm light is accredited to the photoexcitation of intracellular porphyrin molecules resulting in energy transfer and the generation of reactive oxygen species that impart cellular oxidative damage. The specific mechanism of cellular damage, however, is not fully understood. Previous work has suggested that destruction of nucleic acids may be responsible for inactivation; however, microscopic imaging has suggested membrane damage as a major constituent of cellular inactivation. This study investigates the membrane integrity of Escherichia coli and Staphylococcus aureus exposed to 405 nm light. Results indicated membrane damage to both species, with loss of salt and bile tolerance by S. aureus and E. coli, respectively, consistent with reduced membrane integrity. Increased nucleic acid release was also demonstrated in 405 nm light-exposed cells, with up to 50 % increase in DNA concentration into the extracellular media in the case of both organisms. SYTOX green fluorometric analysis, however, demonstrated contradictory results between the two test species. With E. coli, increasing permeation of SYTOX green was observed following increased exposure, with >500 % increase in fluorescence, whereas no increase was observed with S. aureus. Overall, this study has provided good evidence that 405 nm light exposure causes loss of bacterial membrane integrity in E. coli, but the results with S. aureus are more difficult to explain. Further work is required to gain greater understanding of the inactivation mechanism in different bacterial species, as there are likely to be other targets within the cell that are also impaired by the oxidative damage from photo-generated reactive oxygen species.
authors: Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, 204 George Street, Glasgow, Scotland G1 1XW, UK.
authors: Karen
authors: K
authors: McKenzie
authors: Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, 204 George Street, Glasgow, Scotland G1 1XW, UK.|Department of Biomedical Engineering, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow, Scotland G4 0NW, UK.
authors: Michelle
authors: M
authors: Maclean
authors: Department of Biomedical Engineering, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow, Scotland G4 0NW, UK.
authors: M Helen
authors: MH
authors: Grant
authors: Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, 204 George Street, Glasgow, Scotland G1 1XW, UK.|Department of Biomedical Engineering, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow, Scotland G4 0NW, UK.
authors: Praveen
authors: P
authors: Ramakrishnan
authors: Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, 204 George Street, Glasgow, Scotland G1 1XW, UK.
authors: Scott J
authors: SJ
authors: MacGregor
authors: Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, 204 George Street, Glasgow, Scotland G1 1XW, UK.
authors: John G
authors: JG
authors: Anderson
mesh_terms: D001647:Bile Acids and Salts / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*; D004926:Escherichia coli / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects*; D005456:Fluorescent Dyes / Q000737:chemistry; D008027:Light; D009930:Organic Chemicals / Q000737:chemistry; D010084:Oxidation-Reduction; D012965:Sodium Chloride / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects*
chemical_list: D001647:Bile Acids and Salts; D005456:Fluorescent Dyes; D009930:Organic Chemicals; C402795:SYTOX Green; D012965:Sodium Chloride