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Escherichia coli is killed by 405 nm blue light due to its endogenous porphyrins induced by 5-aminolevulinic acid
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.ORCID iD: 0000-0002-5759-4861
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Antimicrobial phototherapy without the use of an exogenous photosensitizer has been suggested to be a complement to antibiotics.  A commonly accepted hypothesis is that bacteria are producing endogenous porphyrins that may act as photosensitizers. To our best knowledge there are no studies linking the production of singlet oxygen for naturally occurring porphyrins to the bacterial porphyrin content, and the photosensitivity of bacteria. In the present study, we determined the quantum yield of singlet oxygen for three porphyrins commonly detected in bacteria. Porphyrin content in E. coli was determined by HPLC-MS/MS before and after administration of 5-aminolaevulinic acid (5-ALA) to the cultivation broth. 5-aminolaevulinic acid is a porphyrin precursor and will induce high amounts of intracellular porphyrins. Cultures of E. coli grown with and without 5-ALA were illuminated with 405 nm light at different light doses. Relative to the amount, uroporphyrin demonstrated the highest quantum yield of singlet oxygen, followed by coproporphyrin and protoporphyrin IX. E. coli was analyzed for porphyrin content and only low amounts of coproporphyrin I, coproporphyrin III and protoporphyrin IX could be detected. In addition, E. coli showed no sensitivity for 405 nm light at the highest dose (172.8 J/cm2). However, when E. coli was grown in 5 mM 5-ALA for 48 h, the intracellular content of porphyrins increased remarkably. Uroporphyrin was the most abundant porphyrin with 48% of total porphyrin content. Addition of 5-ALA also made E. coli more sensitive for blue light. A light dose of 4.8 J/cm2 reduced viable E. coli with 3 log10 steps and at a light dose of 57.6 J/cm2 the killing efficiency was higher than the level to work as an disinfectant (>5 log10 steps). These results shows that E. coli is be killed by light due to its endogenously produced porphyrins and that uroporphyrin could play an important part in these mechanisms.  

National Category
Analytical Chemistry
Research subject
Analytical Chemistry
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URN: urn:nbn:se:su:diva-149379OAI: oai:DiVA.org:su-149379DiVA: diva2:1161253
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2017-12-04Bibliographically approved
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