The effects of violet and blue light irradiation on ESKAPE pathogens and human cells in presence of cell culture media

The potential role of violet-blue light to preventing hospital acquired infections: a systematic review

Healthcare-associated infections (HAIs) are a major challenge in modern healthcare, leading to increased mortality, financial burden and negative societal impact. The World Health Organization (WHO) and others have highlighted the alarming rise in HAIs, exacerbated by antimicrobial resistance (AMR), which further complicates treatment. The efficacy of violet-blue light (VBL) technology (approximately 405–420 nm) in inactivating various pathogens and its safety for human exposure have been extensively studied. This study analyses the scientific literature on the use of VBL as a disinfection method in health care settings, with cost and safety implications. It discusses VBL in comparison to other disinfection methods, the implications of its use, and its potential in reducing HAIs due to its ability to be used in occupied environments. While UV technology is more effective at bacterial inactivation, the continuous application of VBL compensates for this difference. UV and VBL technologies have a positive environmental impact, eliminating the need for consumables and reducing waste. Safety concerns are very limited for VBL compared to UV when properly used. The literature highlights that implementing VBL can be a significant step in continuous environmental disinfection in both healthcare and domestic settings. VBL is safe for occupants and offers a feasible, green method for combating environmental contamination and potentially reducing HAIs.

Decontamination of patient bathroom surfaces with 405 nm violet-blue light irradiation in a real-life setting

BACKGROUND

Irradiation with violet-blue light (VBL), in the spectrum of 405-450 nm, has been reported to be effective against pathogenic bacteria.

AIM

To investigate whether VBL irradiation could reduce the level of surface contamination at seven shared patient bathrooms in two wards at a hospital in Sweden.

METHODS

Repeated sampling of five separate surfaces (door handle, tap water handle, floor, toilet seat, and toilet armrest) was performed in the bathrooms where 405 nm light-emitting diode spotlights had been installed. A prospective study with a cross-over design was carried out, which included two study periods, first with the spotlights either switched on or off and a second study period with the opposite spotlight status.

FINDINGS

In total, 665 surface samples were collected during the study (133 samples per surface). Bacterial growth was found in 84% of all samples. The most common findings were coagulase-negative staphylococci and Bacillus spp. The median number of colony-forming units (cfu)/cm2 was 15 (interquartile range: 5-40) for all surfaces. In our main outcome, mean cfu/cm2 of all surfaces in a bathroom, no difference was observed with or without VBL. Clean surfaces (<5 cfu/cm2) were more commonly observed in bathrooms with VBL, also when controlling for confounding factors. No difference was observed in the number of heavily contaminated surfaces.

CONCLUSION

This study did not safely demonstrate an additive effect on bacterial surface levels when adding VBL to routine cleaning in shared patient bathrooms.

Exploration of the Graphene Quantum Dots-Blue Light Combination: A Promising Treatment against Bacterial Infection

Graphene Quantum Dots (GQDs) have shown the potential for antimicrobial photodynamic treatment, due to their particular physicochemical properties. Here, we investigated the activity of three differently functionalized GQDs-Blue Luminescent GQDs (L-GQDs), Aminated GQDs (NH2-GQDs), and Carboxylated GQDs (COOH-GQDs)-against E. coli. GQDs were administrated to bacterial suspensions that were treated with blue light. Antibacterial activity was evaluated by measuring colony forming units (CFUs) and metabolic activities, as well as reactive oxygen species stimulation (ROS). GQD cytotoxicity was then assessed on human colorectal adenocarcinoma cells (Caco-2), before setting in an in vitro infection model. Each GQD exhibits antibacterial activity inducing ROS and impairing bacterial metabolism without significantly affecting cell morphology. GQD activity was dependent on time of exposure to blue light. Finally, GQDs were able to reduce E. coli burden in infected Caco-2 cells, acting not only in the extracellular milieu but perturbating the eukaryotic cell membrane, enhancing antibiotic internalization. Our findings demonstrate that GQDs combined with blue light stimulation, due to photodynamic properties, have a promising antibacterial activity against E. coli. Nevertheless, we explored their action mechanism and toxicity on epithelial cells, fixing and standardizing these infection models.

Natural Phytochemical and Visible Light at Different Wavelengths Show Synergistic Antibacterial Activity against Staphylococcus aureus

As the risk of antibiotic-resistant bacteria increases, interest in non-antibiotic treatment is also increasing. Among the methods used in non-antibiotic therapy, natural antibiotics such as essential oils have disadvantages such as low efficiency. In the case of phototherapy, the light used for antibacterial activities has low penetration into the human body because of its short wavelength, making it of low medical utility. To solve this problem, this study aimed to determine conditions for enhancing the antibacterial activity of natural phytochemicals and visible light. Four natural phytochemical extracts that showed high antibacterial properties in previous studies were analyzed. Synergistic effects on antibacterial activity and cytotoxicity were determined when natural phytochemical extracts and visible light were simultaneously used. As a result, it was confirmed that the antibacterial activity increased by four times when Sanguisorba officinalis L. was irradiated with 465 nm for 10 min and 520 nm for 40 min, and Uncaria gambir Roxb. was irradiated with 465 nm for 10 min and 520 nm for 60 min compared to when Sanguisorba officinalis L. and Uncaria gambir Roxb. were used alone. The synergistic effect on antibacterial activity was independent of the absorption peak of the natural phytochemical extracts. In addition, in the case of natural phytochemical extracts with improved antibacterial activity, it was confirmed that the improvement of antibacterial activity was increased in inverse proportion to the light irradiation wavelength and in proportion to the light irradiation time. The antibacterial activity was enhanced regardless of antibiotic resistance. In the case of cytotoxicity, it was confirmed that there was no toxicity to A549 cells when treated with 465 nm, the shortest wavelength among the natural phytochemical extracts. These results show how to replace blue light, which has been underutilized due to its low transmittance and cytotoxicity. They also demonstrate the high medical potential of using natural phytochemical and visible light as a combination therapy.

Photodegradable by Yellow-Orange Light degFusionRed Optogenetic Module with Autocatalytically Formed Chromophore

Optogenetic systems driven by yellow-orange light are required for the simultaneous regulation of several cellular processes. We have engineered the red fluorescent protein FusionRed into a 26 kDa monomeric optogenetic module, called degFusionRed. Unlike other fluorescent protein-based optogenetic domains, which exhibit light-induced self-inactivation by generating reactive oxygen species, degFusionRed undergoes proteasomal degradation upon illumination with 567 nm light. Similarly to the parent protein, degFusionRed has minimal absorbance at 450 nm and above 650 nm, making it spectrally compatible with blue and near-infrared-light-controlled optogenetic tools. The autocatalytically formed chromophore provides degFusionRed with an additional advantage over most optogenetic tools that require the binding of the exogenous chromophores, the amount of which varies in different cells. The degFusionRed efficiently performed in the engineered light-controlled transcription factor and in the targeted photodegradation of the protein of interest, demonstrating its versatility as the optogenetic module of choice for spectral multiplexed interrogation of various cellular processes.

Inhibitory effect of 405 nm laser light on bacterial biofilm in urethral stent

The clinical use of urethral stents is usually complicated by various adverse effects, including dysuria, fever, and urinary tract infection (UTI). Biofilms (formed by bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) adhering to the stent cause UTIs in stented patients (approximately 11%). The undesirable consequences of antibiotics use include bacterial resistance, weight gain, and type 1 diabetes, which occur when antibiotics are used for a long time. We aimed to assess the efficacy of a new optical treatment with a 405 nm laser to inhibit bacterial growth in a urethral stent in vitro. The urethral stent was grown in S. aureus broth media for three days to induce biofilm formation under dynamic conditions. Various irradiation times with the 405 nm laser light were tested (5, 10, and 15 min). The efficacy of the optical treatment on biofilms was evaluated quantitatively and qualitatively. The production of reactive oxygen species helped eliminate the biofilm over the urethral stent after 405 nm irradiation. The inhibition rate corresponded to a 2.2 log reduction of colony-forming units/mL of bacteria after 0.3 W/cm² of irradiation for 10 min. The treated stent showed a significant reduction in biofilm formation compared with the untreated stent, as demonstrated by SYTO 9 and propidium iodide staining. MTT assays using the CCD-986sk cell line revealed no toxicity after 10 min of irradiation. We conclude that optical treatment with 405 nm laser light inhibits bacterial growth in urethral stents with no or minimal toxicity.

Structural modification of the Pseudomonas aeruginosa alkylquinoline cell-cell communication signal, HHQ, leads to benzofuranoquinolines with anti-virulence behaviour in ESKAPE pathogens

Microbial populations have evolved intricate networks of negotiation and communication through which they can coexist in natural and host ecosystems. The nature of these systems can be complex and they are, for the most part, poorly understood at the polymicrobial level. The Pseudomonas Quinolone Signal (PQS) and its precursor 4-hydroxy-2-heptylquinoline (HHQ) are signal molecules produced by the important nosocomial pathogen Pseudomonas aeruginosa . They are known to modulate the behaviour of co-colonizing bacterial and fungal pathogens such as Bacillus atropheaus, Candida albicans and Aspergillus fumigatus. While the structural basis for alkyl-quinolone signalling within P. aeruginosa has been studied extensively, less is known about how structural derivatives of these molecules can influence multicellular behaviour and population-level decision-making in other co-colonizing organisms. In this study, we investigated a suite of small molecules derived initially from the HHQ framework, for anti-virulence activity against ESKAPE pathogens, at the species and strain levels. Somewhat surprisingly, with appropriate substitution, loss of the alkyl chain (present in HHQ and PQS) did not result in a loss of activity, presenting a more easily accessible synthetic framework for investigation. Virulence profiling uncovered significant levels of inter-strain variation among the responses of clinical and environmental isolates to small-molecule challenge. While several lead compounds were identified in this study, further work is needed to appreciate the extent of strain-level tolerance to small-molecule anti-infectives among pathogenic organisms.

Exploring the Multifunctionality of Mechanochemically Synthesized γ-Alumina with Incorporated Selected Metal Oxide Species

γ-Alumina with incorporated metal oxide species (including Fe, Cu, Zn, Bi, and Ga) was synthesized by liquid-assisted grinding-mechanochemical synthesis, applying boehmite as the alumina precursor and suitable metal salts. Various contents of metal elements (5 wt.%, 10 wt.%, and 20 wt.%) were used to tune the composition of the resulting hybrid materials. The different milling time was tested to find the most suitable procedure that allowed the preparation of porous alumina incorporated with selected metal oxide species. The block copolymer, Pluronic P123, was used as a pore-generating agent. Commercial γ-alumina (S_BET = 96 m²·g^-1), and the sample fabricated after two hours of initial grinding of boehmite (S_BET = 266 m²·g^-1), were used as references. Analysis of another sample of γ-alumina prepared within 3 h of one-pot milling revealed a higher surface area (S_BET = 320 m²·g^-1) that did not increase with a further increase in the milling time. So, three hours of grinding time were set as optimal for this material. The synthesized samples were characterized by low-temperature N₂ sorption, TGA/DTG, XRD, TEM, EDX, elemental mapping, and XRF techniques. The higher loading of metal oxide into the alumina structure was confirmed by the higher intensity of the XRF peaks. Samples synthesized with the lowest metal oxide content (5 wt.%) were tested for selective catalytic reduction of NO with NH₃ (NH₃-SCR). Among all tested samples, besides pristine Al₂O₃ and alumina incorporated with gallium oxide, the increase in reaction temperature accelerated the NO conversion. The highest NO conversion rate was observed for Fe₂O₃-incorporated alumina (70%) at 450 °C and CuO-incorporated alumina (71%) at 300 °C. The CO₂ capture was also studied for synthesized samples and the sample of alumina with incorporated Bi₂O₃ (10 wt.%) gave the best result (1.16 mmol·g^-1) at 25 °C, while alumina alone could adsorb only 0.85 mmol·g^-1 of CO₂. Furthermore, the synthesized samples were tested for antimicrobial properties and found to be quite active against Gram-negative bacteria, P. aeruginosa (PA). The measured Minimum Inhibitory Concentration (MIC) values for the alumina samples with incorporated Fe, Cu, and Bi oxide (10 wt.%) were found to be 4 µg·mL^-1, while 8 µg·mL^-1 was obtained for pure alumina.

Direct dentin bleaching: Would it be possible?

This study aims to evaluate in vitro the effect of violet LED when applied directly to dentin tissue pigmented by different substances. We analyzed the chromatic alteration, the bleaching effect and the temperature variation. Hence, 60 bovine dentin tissue discs were divided into five groups: NNatural Pigmentation; T-Black Tea; C-Soluble Coffee; W-Red Wine; B-Equine Blood. Individualized pigmentation protocols were performed and all groups reached the same chromatic change value. Subsequently, we simultaneously performed a bleaching session and measured temperature variation using a K-type thermocouple device. Data on chromatic change (∆E, ∆E00, ∆a, ∆b and ∆L), whitening effect (WID) and temperature variation were subjected to one-way Anova and Tukey's post-test at a 5% significance level. The C group showed the most relevant chromatic change values, similar to the N group, responding positively to the treatment. However, the B group differed from the control group, which showed difficulty to respond to the treatment. Regarding the whitening index, only the W group showed lower results than the others. The B group showed the greatest temperature changes. We conclude that the violet LED offered chromatic change, which generated a bleaching effect. Pigmentations with red wine and blood showed the greatest difficulty to respond to treatment, also promoting a higher temperature rise in teeth pigmented with blood.

Efficacy of violet-blue light to inactive microbial growth

The increase in health care-associated infections and antibiotic resistance has led to a growing interest in the search for innovative technologies to solve these problems. In recent years, the interest of the scientific community has focused on violet-blue light at 405 nm (VBL405). This study aimed to assess the VBL405 efficiency in reducing microbial growth on surfaces and air. This descriptive study run between July and October 2020. Petri dishes were contaminated with P. aeruginosa, E. coli, S. aureus, S. typhimurium, K. pneumoniae and were placed at 2 and 3 m from a LED light source having a wavelength peak at 405 nm and an irradiance respectively of 967 and 497 µW/cm². Simultaneously, the air in the room was sampled for 5 days with two air samplers (SAS) before and after the exposition to the VBL405 source. The highest microbial reduction was reached 2 m directly under the light source: S. typhimurium (2.93 log₁₀), K. pneumoniae (2.30 log₁₀), S. aureus (3.98 log₁₀), E. coli (3.83 log₁₀), P. aeruginosa (3.86 log₁₀). At a distance of 3 m from the light source, the greatest reduction was observed for S. aureus (3.49 log₁₀), and P. aeruginosa (3.80 log₁₀). An average percent microbial reduction of about 70% was found in the sampled air after 12 h of exposure to VBL405. VBL405 has proven to contrast microbial growth on the plates. Implementing this technology in the environment to provide continuous disinfection and to control microbial presence, even in the presence of people, may be an innovative solution.

Violet-blue Light Induces "Natural" Photodynamic Plasma Disinfection with Endogenous Sensitizers

Naturally, endogenous porphyrins can provide sensitized disinfection power, and to photobiologists' delight, violet-blue light has potential virtues. But progress is needed before violet-blue light treatment can used for microbe treatment of blood samples, and yet safeguard against plasma protein photooxidation. A report by Maclean et al. in this issue of Photochemistry & Photobiology on microbe reduction of blood samples showing negligible competing protein photooxidation may bring that goal a step closer.