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Forum Blue light as an antimicrobial intervention?

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1. Nick Waterfield Staff Warwick Medical School

   #1 16:55, Tue 12 Apr 2016

   Hi AMR people

   Photo-activation of "killer" compounds is one use for light therapy but it also seems light alone can act as an antimicrobial (see abstract below). My model Pathogen Photorhabdus produces blue light as bioluminesence (and has an orange/yellow/red pigment(s) - as protection?). I suspect it may be using its 425nm light emission to give it an advantage against competing bacteria in the corpse of the insect it has killed (and is eating). 

   I would be interested in designing a blue LED based system for testing this. Any ideas on a rig we could make for this from the Physics/Engineering folk? I attached an experiment I did a couple of years ago that suggested the colony formation of Photorhabdus itself can also be inhibited by blue (and white) light. 

   Idea thoughts would be welcome.

   Crazy/vague ideas such as:

   (1) Could catherters/bandages be made of optical material through which you shine strong blue light to prevent biofilm formation for example?

   (2) Shine strong blue light through dialysis blood if infection occurs?

   (3) Implant blue light emitting devices to reduce infections in vivo (bladder, colon?)

   (4) Blue lasers as a way to clean ulcerations?

   You get the idea....

   Curr Pharm Des. 2015;21(16):2109-21.
   Harnessing the power of light to treat staphylococcal infections focusing on MRSA.
   Agrawal T, Avci P, Gupta GK, Rineh A, Lakshmanan S, Batwala V, Tegos GP, Hamblin MR1.
   Abstract: Methicillin-resistant Staphylococcus aureus (MRSA) has become the most important drug-resistant microbial pathogen in countries throughout the world. Morbidity and mortality due to MRSA infections continue to increase despite efforts to improve infection control measures and to develop new antibiotics. Therefore alternative antimicrobial strategies that do not give rise to development of resistance are urgently required. A group of therapeutic interventions has been developed in the field of photomedicine with the common theme that they rely on electromagnetic radiation with wavelengths between 200 and 1000 nm broadly called "light". These techniques all use simple absorption of photons by specific chromophores to deliver the killing blow to microbial cells while leaving the surrounding host mammalian cells relatively unharmed. Photodynamic inactivation uses dyes called photosensitizers (PS) that bind specifically to MRSA cells and not host cells, and generate reactive oxygen species including singlet oxygen and singlet oxygen upon illumination. Sophisticated molecular strategies to target the PS to MRSA cells have been designed. Ultraviolet C radiation can damage microbial DNA without unduly harming host DNA. Blue light can excite endogenous porphyrins and flavins in MRSA cells that are not present in host cells. Near-infrared lasers can interfere with microbial membrane potentials without raising the temperature of the tissue. Taken together these innovative approaches towards harnessing the power of light suggest that the ongoing threat of MRSA may eventually be defeated.

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   • PDF document effect_of_light.pdf
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2. Marco Polin Staff Physics

   #2 17:31, Tue 12 Apr 2016

   If you want to monitor the growth of the colonies, I have downstairs a little rig which two MSc students have put together this a.y. to study bacterial swarming at the ~mm level (working with me and Munehiro). The field of view is quite large. Don't remember how much but it should be at least 5cm. I haven't characterised the resolution, but it should be better than 0.5mm.

   The setup is based on a DSLR camera and it can take 1Mb pics at regular intervals until it fills the SD card, so thousands of images. This would allow you to follow colony growth in time. The students were using it with a white LED ring, but i have a homemade IR LED ring which we could try. We also have a high-intensity blue LED which should be straightforward to combine with the rest.

   Marco

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3. Munehiro Asally Staff Life Sciences

   #3 18:04, Tue 12 Apr 2016 (edited 18:05, Tue 12 Apr 2016)

   I used this LED (£40) to make a "blue room" for my bacteria. We observe blue-light sensitve biofilm formation and pigment formations, which we are currently working on (on the side, though).  The spectra of the LED is probably broad and it won't give you any precise spectra around 425nm, but maybe good enough for developing ideas. You are more than welcome to use my LED if interested. 

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4. Nick Waterfield Staff Warwick Medical School

   #4 10:37, Wed 13 Apr 2016

   Both

   Thanks for the info and your ideas. I think there could be some good scope for a collaboration on several points.

   (1) I think it would be very interesting to look at how antibiotic sensitive and resistant bacteria respond both in growth rate (division) and (for those that can) motility when bathed in blue light vs dark. It would also be interesting to check for synagistic effects of blue light with known antibiotics.

   
   (2) How does Photorhabdus itself responds to blue light? It is possible that it may use its own blue light emission as a quorum sensing single to syncronize bacterial developmental states across the highly heterogeneic environment of an infected insect in the soil. Given its life cycle it has to co-ordinate its virulence vs symbiotic state with a replicating symbiotic nematode in an infected insect. Chemical gradients may not be consistent enough, so it may have adapted to using light signals. If a bacteria has naturally evolved to produce and sense its own light signals (and simulateously communicating with the nematode partner) it would be a first and of wide general interest I feel.

   
   The enzymes of the Photorhabdus lux reaction in theory produce 490nm blue/green light accroding to the liturature (in E.coli), however I know some bacteria also make lumazines which can modulate the wavelength. This may be happening in Photorhabdus but I can't find an good reference where anyone has actually measured the wavelength directly. Anyway my previous work has shown that while the bacteria make the light during planktonic growth, that they also switch to strong production when forming a biofilm (attached) as highlighted by use of a biofilm deficient mutant. We dont know what quorum sensing signal they use to regulate light (if indeed there is one) but it is not a AHL as far as we can tell.

   Nick

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   • PDF document photorhabdus_lux_in_biofilms.pdf
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