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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
Identifiers
URN: urn:nbn:se:su:diva-149379OAI: oai:DiVA.org:su-149379DiVA, id: diva2:1161253
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Porphyrins and heme in microorganisms: Porphyrin content and its relation to phototherapy and antimicrobial treatments in vivo and in vitro
Open this publication in new window or tab >>Porphyrins and heme in microorganisms: Porphyrin content and its relation to phototherapy and antimicrobial treatments in vivo and in vitro
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the greatest threats to human health is increasing antimicrobial resistance among pathogens, and finding alternatives for treatment of bacterial infections is of highest importance together with a more controlled use of antibiotics. Porphyrins and heme have both been shown to be a promising class of compounds for inactivation of bacteria; porphyrins by their excellent properties to act as a photosensitizer, and heme by its importance as an iron source during a bacterial infection in vertebrates.

This thesis describes the development of analytical methods for the identification and determination of porphyrins and heme using liquid chromatography coupled to tandem mass spectrometry. Subsequently, these developed methods were applied to bacterial samples to investigate different culture conditions and additives effect to the intracellular porphyrin and heme composition. Singlet oxygen production of three naturally occurring porphyrins have been determined together with the photosensitivity for blue light and the porphyrin content in E. coli. Toothbrushes equipped with a LED, emitting light with a wavelength of 450 nm, were used in an eight week randomized clinical trial to investigate any positive periodontal effect of blue light.

Porphyrin and heme content in Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis were highly affected by the different cultivation conditions. The culture age of A. actinomycetemcomitans affected the porphyrin profile, while only small changes were observed for P. gingivalis during growth. A large change of the porphyrin profile could be observed when the bacteria were passaged onto a new growth medium. Additional porphyrins were detected and the total porphyrin content increased up to 28 times. These findings highlight the need for more standardized cultivation procedures when performing in vitro experiments.

Heme content in Escherichia coli was affected when different additives related to biosynthesis of heme were added to the growth medium. The uptake of heme could be reduced with 52% when a compound that chemically looks similar to heme was added to the growth medium. Since heme acquisition is important for many pathogens, this could be a promising target for antimicrobial drugs.

E. coli showed no sensitivity for 405 nm light using light doses up to 172.8 J/cm2 and only low concentrations of porphyrins could be quantified. By adding a porphyrin precursor to E. coli the intracellular concentration of porphyrins increased remarkably and a light dose of 57.6 J/cm2 reduced the bacterial number with > 5 log10 steps. This shows that E. coli can be killed due to their endogenous porphyrins.

In the clinical study we could see a weak trend that the 450 nm LED toothbrush possessed a phototherapeutic effect for three clinical indices. All indices were decreased in the intervention group, but there were no statistically significant difference compared to the control group. However, four inflammation markers were significantly decreased in the intervention group while only one decreased significantly in the control group.

In conclusion, this thesis has shown that porphyrins and heme are produced endogenously in microorganisms and that the porphyrin profiles vary depending on culture conditions and different additives. Furthermore, porphyrins may be used as endogenous photosensitizers to inactivate bacteria, but more research is necessary to determine if there is a specific porphyrin that contributes more to the photosensitivity.

Place, publisher, year, edition, pages
Stockholm: Department of environmental science and analytical chemistry, Stockholm university, 2017
Keyword
Porphyrins, heme, phototherapy, antimicrobial resistance, singlet oxygen, photosensitizer, bacteria, HPLC-MS/MS, oral bacteria, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Escherichia coli
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:su:diva-149405 (URN)978-91-7797-079-8 (ISBN)978-91-7797-080-4 (ISBN)
Public defence
2018-01-19, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2017-12-21 Created: 2017-11-30 Last updated: 2017-12-20Bibliographically approved

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