Lethal Photosensitization Research Articles

Power of Amplified Light Against Chromogenic Bacterial Stains - A Case Report

The treatment of black stains has always been a grey area for the dentists to deal with due to its recurrence. The more effective treatments in current literature are lactoferrin, diode laser, laser Nd:YAG and phototherapy. An attempt was made to remove the stain using low level laser therapy with the similar principle of lethal laser photosensitization and photodynamic therapy without the use of any dye. Our study showed a positive result with the reduction of black stains over a period of 1 year. Hence, the use of LLLT could be considered as one of the adjunct treatment modality for chromogenic bacterial stains. Keywords: Black stains, Biostimulation, Chromogenic bacterial stains, Diode laser, Low level laser therapy

The Antibacterial Activity of Hydroxyapatite-Tryptophan Complex with Gray Titania by Photocatalysis Using LED Diodes.

Peri-implantitis is an important biologic complication that can lead to implant failure. Proper treatment should effectively kill bacteria, not harm the implant surface, and promote regeneration. Recently, photocatalytic coating without antibiotics or external agents was proposed to be an alternative to antibiotic therapy. The aim of this study was to evaluate the photocatalytic antibacterial effect of a new titanium implant coating made from hydroxyapatite-tryptophan complex and gray titania, which was activated by two visible lights. Titanium alloy substrate was plasma sprayed with hydroxyapatite (80 wt%) and dititanium trioxide (20 wt%) and then pressed with tryptophan. Three bacteria related to peri-implantitis, Porphyromonas gingivalis, Tannerella forsythia, and Aggregatibacter actinomycetemcomitans, were used in this study. Six conditions were tested: (1) control group (only bacteria), (2) photocatalytic sample in darkness (bacteria and coated sample in darkness), (3) red laser for 15 minutes (bacteria irradiated with photoactivated disinfection [PAD] light, 650-nm wavelength), (4) broadband light-emitting diode (LED) for 15 minutes (bacteria irradiated with broadband LED, peak wavelength at 470 nm), (5) photocatalysis by red laser for 15 minutes (bacteria and coated sample irradiated with PAD light), and (6) photocatalysis by broadband LED for 15 minutes (bacteria and coated sample irradiated with broadband LED). After 15 minutes of irradiation, photocatalytic antibacterial effects were evaluated by total viable bacterial count, adenosine triphosphate (ATP) assay, and LIVE/DEAD assay. The number of all bacteria tested was significantly decreased by the photocatalytic effect of both visible light sources (P < .05). For P gingivalis, viable bacteria of lethal photosensitization groups were also significantly decreased (P < .05), especially when using the broadband LED. However, the coating material itself did not have antibacterial properties without light activation. There was no significant difference in ATP among groups (P > .05). LIVE/DEAD staining showed that red fluorescent bacterial cells were present in photocatalytic groups from the two light sources. Photoactivated hydroxyapatite-tryptophan complex and gray titania as a photocatalytic coating has antibacterial effects on bacteria associated with peri-implantitis.

Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus aureus Cells.

The photodynamic activity of Neutral Red and the new monobrominated Neutral Red was studied in suspensions of Staphylococcus aureus. The effect of mannitol and sodium azide in the presence of 25 μm photosensitizer on lethal photosensitization were investigated. The results of the mechanistic evaluation of Neutral Red showed that both mannitol and sodium azide produced a completed protective effect after irradiation without significant differences between them. The evaluation of monobrominated Neutral Red also showed a protective effect of microorganisms with the addition of mannitol. Although sodium azide produced a protective effect of the photoinactivation, it was incomplete and less than that exhibited by mannitol. The results indicate that the starting reagent, Neutral Red, is a producer of radical species, acting through a type I mechanism, whereas the halogenated derivative of Neutral Red produced reactive oxygen species and a contribution of singlet molecular oxygen cannot be discarded in the photoinactivation of Staphylococcus aureus cells. These results, analyzed together with the previously evaluated properties of the dyes, allow us to explain the differences observed in the photoinactivation of Staphylococcus aureus mediated by both azine photosensitizers.

5-aminolevulinic acid-mediated photodynamic therapy and its strain-dependent combined effect with antibiotics on Staphylococcus aureus biofilm.

Staphylococcus aureus (S. aureus) is hard to be eradicated, not only due to the emergence of antibiotic resistant strains but also because of its ability to form biofilm. Antibiotics are the major approach to treating biofilm infections, but their effects are unsatisfactory. One of the potential alternative treatments for controlling biofilm infections is photodynamic therapy (PDT), which requires the administration of photosensitizer, followed by light activation. 5-aminolevulinic acid (ALA), a natural photosensitizer prodrug, presents favorable characteristics, such as easy penetration and rapid clearance. These advantages enable ALA-based PDT (ALA-PDT) to be well-tolerated by patients and it can be repeatedly applied without cumulative toxicity or serious side effects. ALA-PDT has been proven to be an effective treatment for multidrug resistant pathogens; however, the study of its effect on S. aureus biofilm is limited. Here, we established our PDT system based on the utilization of ALA and a light-emitting diode, and we tested the effect of ALA-PDT on S. aureus biofilm as well as the combined effect of ALA-PDT and antibiotics on S. aureus biofilm. Our results showed that ALA-PDT has a strong antibacterial effect on S. aureus biofilm, which was confirmed by the confocal laser scanning microscope. We also found that lethal photosensitization occurred predominantly in the upper layer of the biofilm, while the residual live bacteria were located in the lower layer of the biofilm. In addition, the improved bactericidal effect was observed in the combined treatment group but in a strain-dependent manner. Our results suggest that ALA-PDT is a potential alternative approach for future clinical use to treat S. aureus biofilm-associated infections, and some patients may benefit from the combined treatment of ALA-PDT and antibiotics, but drug sensitivity testing should be performed in advance.

Light activated antimicrobial agents can inactivate oral malodour causing bacteria

Oral malodour is a common condition which affects a large proportion of the population, resulting in social, emotional and psychological stress. Certain oral bacteria form a coating called a biofilm on the tongue dorsum and degrade organic compounds releasing volatile sulfur compounds that are malodourous. Current chemical treatments for oral malodour such as mouthwashes containing chlorhexidine or essential oils, are not sufficiently effective at reducing the bacterial load on the tongue. One potential alternative to current chemical treatments for oral malodour is the use of light activated antimicrobial agents (LAAAs), which display no toxicity or antimicrobial activity in the dark, but when exposed to light of a specific wavelength produce reactive oxygen species which induce damage to target cells in a process known as photodynamic inactivation.This study aimed to determine whether oral malodour causing bacteria were susceptible to lethal photosensitization. Five bacterial species that are causative agents of oral malodour were highly sensitive to lethal photosensitization and were efficiently killed by methylene blue in conjunction with 665 nm laser light. Between 4.5–5 log10 reductions in the number of viable bacteria were achieved with 20 µM methylene blue and 14.53 J cm−2 laser light for Porphyromonas gingivalis, Prevotella intermedia, Peptostreptococcus anaerobius and Solobacterium moorei. The number of viable cells fell below the limit of detection in the case of Fusobacterium nucleatum.These findings demonstrate that methylene blue in combination with 665 nm laser light is effective at killing bacteria associated with oral malodour, suggesting photodynamic therapy could be a viable treatment option for oral malodour.

Lethal photosensitisation of Prevotellaceae under anaerobic conditions by their endogenous porphyrins

BackgroundOxygen is generally considered essential for lethal photosensitisation by photodynamic processes. The oral anaerobes, Prevotella intermedia and P. nigrescens are known to be photosensitive, but are also extremely sensitive to the cytotoxic effects of oxygen. MethodsThe Prevotellaceae were exposed to two 405nm light sources for different exposure times in an anaerobic chamber. Viable counts of the light exposed samples were compared to light-free controls to determine the proportion of bacteria killed. ResultsLethal photosensitivity was demonstrated against P. intermedia and P. nigrescens. The proportions of bacteria killed by either the light-emitting diode or laser pointer were similar at a given energy density (J/cm2). ConclusionsLethal photosensitivity was demonstrated in two species of Prevotella under anaerobic conditions.

Photodynamic Inactivation of Candida albicans with Imidazoacridinones: Influence of Irradiance, Photosensitizer Uptake and Reactive Oxygen Species Generation.

The increasing applicability of antifungal treatments, the limited range of available drug classes and the emergence of drug resistance in Candida spp. suggest the need for new treatment options. To explore the applicability of C. albicans photoinactivation, we examined nine structurally different imidazoacridinone derivatives as photosensitizing agents. The most effective derivatives showed a >104-fold reduction of viable cell numbers. The fungicidal action of the three most active compounds was compared at different radiant powers(3.5 to 63 mW/cm2), and this analysis indicated that 7 mW/cm2 was the most efficient. The intracellular accumulation of these compounds in fungal cells correlated with the fungicidal activity of all 9 derivatives. The lack of effect of verapamil, an inhibitor targeting Candida ABC efflux pumps, suggests that these imidazoacridinones are not substrates for ABC transporters. Thus, unlike azoles, a major class of antifungals used against Candida, ABC transporter-mediated resistance is unlikely. Electron paramagnetic resonance (EPR)-spin trapping data suggested that the fungicidal light-induced action of these derivatives might depend on the production of superoxide anion. The highest generation rate of superoxide anion was observed for 1330H, 1610H, and 1611. Singlet oxygen production was also detected upon the irradiation of imidazoacridinone derivatives with UV laser light, with a low to moderate yield, depending on the type of compound. Thus, imidazoacridinone derivatives examined in the present study might act via mixed type I/type II photodynamic mechanism. The presented data indicate lack of direct correlation between the structures of studied imidazoacridinones, cell killing ability, and ROS production. However, we showed for the first time that for imidazoacridinones not only intracellular accumulation is necessary prerequisite of lethal photosensitization of C. albicans, but also localization within particular cellular structures. Our findings present IA derivatives as efficient antifungal photosensitizers with a potential to be used in local treatment of Candida infection.

Synergic phototoxic effect of visible light or Gallium-Arsenide laser in the presence of different photo-sensitizers on Porphyromonas gingivalis and Fusobacterium nucleatum.

Background:According to the development of resistant strains of pathogenic bacteria following treatment with antimicrobial chemotherapeutic agents, alternative approaches such as lethal photosensitization are being used. The aim of this study was to evaluate the effect of visible light and laser beam radiation in conjugation with three different photosensitizers on the survival of two main periodontopathogenic bacteria including Porphyromonas gingivalis and Fusobacterium nucleatum in different exposure periods.Materials and Methods:In this in vitro prospective study, strains of P. gingivalis and F. nucleatum. were exposed to visible light at wavelengths of 440 nm and diode laser light, Gallium-Arsenide, at wavelength of 830 nm in the presence of a photosensitizer (erythrosine, curcuma, or hydrogen peroxide). They were exposed 1-5 min to each light. Each experiment was repeated 3 times for each strain of bacteria. Data were analyzed by two-ways ANOVA and least significant difference post-hoc tests. P < 0.05 was considered as significant. After 4 days the colonies were counted.Results:Viability of P. gingivalis was reduced 10% and 20% subsequent to exposure to visible light and diode laser, respectively. The values were 65% and 75% for F. nucleatum in a period of 5-min, respectively. Exposure to visible light or laser beam in conjugation with the photosensitizers suspension caused significant reduction in the number of P. gingivalis in duration of 5-min, suggesting a synergic phototoxic effect. However, the survival rate of F. nucleatum following the exposure to laser with hydrogen peroxide, erythrosine and rhizome of Curcuma longa (curcumin) after 5-min was 10%, 20% and 90% respectively.Conclusion:Within the limitations of this study, the synergic phototoxic effect of visible light in combination with each of the photosensitizers on P. gingivalis and F. nucleatum. However, the synergic phototoxic effect of laser exposure and hydrogen peroxide and curcumin as photosensitizers on F. nucleatum was not shown.

New azine compounds as photoantimicrobial agents against Staphylococcus aureus

Aggregation phenomena of Neutral Red and a new derivative monobrominated Neutral Red were examined in different buffer solutions as a function of dye concentration. The dyes were chemically and photochemically stable and the lipophilicity of the new bromo-compound was characterized by experimental and computer prediction data. In addition, the acid dissociation constant and the singlet molecular oxygen production were determined spectrophotometrically yielding values of 1.16 and 3.14 for Neutral Red and the monobrominated derivative, respectively.The effect of photosensitizer concentration, visible irradiation time and cellular density on lethal photosensitization against Staphylococcus aureus were investigated. The improved physicochemical and photophysical properties of monobrominated Neutral Red were accompanied by a significant increase in the photoantimicrobial action, in conventional-sensitive and -resistant isolates.Based on these results, the dyes exhibited favorable properties; therefore, the new derivative compound could be a promising sensitizer with applications in the photoinactivation of S. aureus.

Biogenic gold nanoparticles enhance methylene blue-induced phototoxic effect on Staphylococcus epidermidis

There is considerable current interest in photodynamic inactivation (PDI) as potential antimicrobial therapy. This study reports successful implementation of PDI of Staphylococcus epidermidis using methylene blue (MB) in combination with biogenic gold nanoparticles (GNP). Monodispersed colloidal GNP were synthesized by reduction of Au+3 in the presence of cell-free filtrate of Trichoderma koningii and were characterized by a number of techniques including UV–Vis and fluorescence spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) to be 12 ± 3 nm spherical gold particles coated with proteins. Studies on the role of the cell-free filtrate proteins in the synthesis of the GNP indicate that the process is nonenzymatic but involves interactions of various amino acids with gold ions. A Xe lamp (550–780 nm) or a He–Ne laser (632 nm) was used as light sources to study the effect of MB alone, the GNP alone, and the MB–GNP mixture on the viability of bacterial cells. Lethal photosensitization of S. epidermidis with the MB–GNP mixture was achieved after 5 and 10 min exposure to laser or Xe lamp, respectively. It has been found that the MB–GNP mixture exhibits a significant antibacterial activity already in the absence of any light source and gives an enhanced antimicrobial response when using either a laser or a Xe lamp source for photosensitization.

Lethal photosensitization of Porphyromonas gingivalis by their endogenous porphyrins under anaerobic conditions: An in vitro study

Lethal photosensitization has been previously demonstrated in Porphyromonas gingivalis, but oxygen is considered to be essential to this process. However, since P. gingivalis is a periodontal pathogen which grows in the low oxygen conditions found in the subgingival crevice, it was considered prudent to study its photosensitivity in anaerobic conditions. A series of experiments were undertaken to attempt to induce lethal photosensitization in P. gingivalis (ATCC 33277) under strict anaerobic conditions using two different 405 nm light sources. Samples of P. gingivalis were grown on a blood-containing, solid growth medium before being suspended in saline and then exposed to 405 nm light delivered by either a hand-held light source (Toothcare™) (11.4 mW/cm(2)) or a laser pointer (328.5 mW/cm(2)). With the exception of the adjustment of the P. gingivalis suspensions to a fixed optical density, the experiments were carried out in their entirety within an anaerobic chamber. The lowest Toothcare light dose tested (0.34 J/cm(2); 30s) yielded a statically significant kill of 63.4% which increased to 94.1% kill at higher light doses (3.42 J/cm(2); 300 s). The laser pointer similarly achieved kills of 90.2% at the lower light dose tested (9.86 J/cm(2); 30s) and 94.5% kill at the highest light dose (98.55 J/cm(2); 300 s). Lethal photosensitization can be instigated in planktonic suspensions of P. gingivalis at 405 nm delivered by hand-held devices under anaerobic conditions. This suggests the possibility that lethal photosensitization occurred by the oxygen-independent type I pathway as oppose to the oxygen-dependent type II pathway.

Photobactericidal polymers; the incorporation of crystal violet and nanogold into medical grade silicone

Crystal violet and 2 nm gold nanoparticles were incorporated into medical grade silicone polymers by use of a novel two-step dipping strategy using water and water–acetone mixtures. Optical microscopic examination showed that the optimised polymer incorporated dye close to the polymer surface, with minimal dye encapsulation throughout the polymer bulk. The modified polymer was stable under aqueous conditions with negligible leaching of crystal violet from the polymer into surrounding aqueous solution at 37 °C. Exposure of the modified silicone to low power 635 nm laser light induced the lethal photosensitisation of both Staphylococcus epidermidis and Escherichia coli. Despite the laser used not matching the absorption maximum of the crystal violet-containing silicone samples, the lethal photosensitisation was the highest reported, in terms of bacterial kill per energy dose. Furthermore, surprisingly, some statistically significant dark kill was also noted.

Synthesis, photophysics and photochemistry of phthalocyanine-ɛ-polylysine conjugates in the presence of metal nanoparticles against Staphylococcus aureus

Abstract This work reports on the photodynamic activity of Zn phthalocyanine-ɛ-polylysine conjugates in the presence of gold and silver nanoparticles (NPs) towards the inactivation of Staphylococcus aureus ( S. aureus ). The conjugates showed high photoinactivation with ∼6% growth at a drug dose of 3 μM and fluence of 39.6 mW/cm 2 for 10 min irradiation time in the presence of silver nanoparticles. The presence of silver nanoparticels from the minimal inhibition concentration (MIC 50 ) studies showed remarkable growth inhibition for the tested conjugates even at low concentrations. The MIC 50 was lowest for the conjugate of 3 with ɛ-polylysine at concentrations of less than 0.0058 μM in the presence of AgNPs. The lethal photosensitization of microorganisms has emerged as a promising treatment since bacteria have reduced possibilities of developing resistance to photodynamic therapy.

Incorporation of methylene blue and nanogold into polyvinyl chloride catheters; a new approach for light-activated disinfection of surfaces

Methylene blue and 2 nm gold nanoparticles were incorporated into commercial PVC catheters by use of a simple “swell–encapsulation–shrink” method using acetone–water mixtures. Neither the methylene blue nor the nanogold leached into aqueous solution and the assemblage was stable to photodegradation upon laser irradiation. Exposure of the modified catheters to red laser light for 4–8 minutes induced the lethal photosensitisation of Staphylococcus epidermidis and Escherichia coli. Results from time-resolved EPR spectroscopy suggested that enhanced methylene blue triplet state production occurs in the presence of 2 nm gold nanoparticles. The implication being that the levels of reactive oxygen species are higher in these co-doped materials than with methylene blue alone.

Phototoxicity of phenothiazinium dyes against methicillin-resistant Staphylococcus aureus and multi-drug resistant Escherichia coli

Photodynamic inactivation (PDI) has been investigated to cope with the increasing incidence of multidrug-resistant (MDR) pathogens. Here we studied the PDI mediated by methylene blue (MB) and toluidine blue O (TBO) in clinical methicillin-resistant Staphylococcus aureus and MDR Escherichia coli, together with their corresponding American Type Culture Collection (ATCC) strains. Effect of photosensitizer concentration (12.5, 25, 50 μg/ml) and laser irradiation time (10, 20 and 30 min) on lethal photosensitization was investigated. TBO was more effective. TBO at 50 μg/ml, 46.8 J cm⁻², exhibited 0.7 log killing for MDR E. coli and 1.7 log killing for E. coli (ATCC 25922); 3.1 log killing for MRSA, and 4.2 log killing for S. aureus (ATCC 25923). MB at 50 μg/ml, 163.8 J cm⁻², only exhibited 2.2 log killing in MRSA and 3.1 log killing in S. aureus (ATCC 25923). MB (50 μg/ml, 163.8 J cm⁻²) induced 0.2 log killing for MDR E. coli and 0.3 log killing for E. coli (ATCC 25922). After TBO-PDI, MDR isolates were more susceptible to some antibiotics than control groups. Our studied clinical isolates were more resistant to PDI-mediated killing than their ATCC reference strains. Thus, TBO/MB-mediated PDI in other MDR isolates deserves further investigation.

Moxifloxacin-gelrite In Situ ophthalmic gelling system against photodynamic therapy for treatment of bacterial corneal inflammation

In this study, six in situ gelling formulations based on Gelrite were prepared and evaluated for the retained ophthalmic delivery of Moxifloxacin (Mox). The effectiveness of the best developed formula G5 was compared with photodynamic therapy (PDT), the recent expanding approach for the treatment of ophthalmologic disorders after the assessment of optimum photodynamic inactivation parameters that permit efficient pathogens eradication. It was found that, Staphylococcus aureus (S. aureus) (Gram-positive) was more susceptible to effective lethal photosensitization that reaches 93.5% reduction in viable count than Escherichia coli (E. coli) (Gramnegative) of 76.1% using 3 mg/mL Hematoporphyrin (HP), illuminated by 630 nm Light Emitting Diode (LED) at 9 J/cm(2) and incubated for 15 min. Following topical instillation of G5 to rabbits corneas, higher amount of Mox was retained in the aqueous humor up to 24 h with significant 6-fold increase in the C(max) and AUC((0-∞)) compared to vigamox commercial eye drops. After post corneal infection with S. aureus, both approaches were effectively treating the infection without causing ocular irritation or collateral damage to corneal tissue where G5 showed remarkable improvement after four days compared to seven days of PDT treatment.

One‐Pot Synthesis of Core‐Shell Silver‐Gold Nanoparticle Solutions and Their Interaction with Methylene Blue Dye

AbstractA one‐pot modified Turkevich synthesis was used to synthesise a range of colloids from pure Ag, through Ag/Au core‐shell mixtures to pure Au by the thermal co‐addition of trisodium citrate to auric acid and silver nitrate mixtures. The colloids were analysed by means of XRD and wide‐beam energy dispersive X‐ray (EDX) analysis. The UV/Vis spectroscopy showed a non‐linear variation in the surface plasmon resonance band with the Au/Ag ratio, consistent with core‐shell formation. High resolution transmission electron microscopy (HRTEM) imaging, in conjunction with thin‐beam EDX line analysis, confirmed the presence of predominantly Ag cores and Au exteriors in the Au/Ag mixture. The argon ion sputtering with X‐ray photoelectron spectroscopy (XPS) measurements of the particles also indicated a Ag‐Au core‐shell formation. Ag0, Au0 and significant levels of AuI states were observed, which correlate with a Ag‐Au core‐shell model where the gold shell becomes partially oxidised at the surface. The subsequent titration of the colloids with methylene blue (MB) dye showed strong positive increases in the extinction coefficient at the absorption maximum. At the optimum levels of dye addition, a linear relationship was found between the average nanoparticle size and the number of dye solvation shells. The pure Au and Ag colloids showed the greatest propensity for an increase in the extinction coefficient of MB due to an enhanced transfer of the surface plasmons to the localised dye molecules and demonstrated the potential for increased functionality as light‐activated agents in the lethal photosensitisation of bacteria.

Susceptibility of Candida albicans, Staphylococcus aureus, and Streptococcus mutans biofilms to photodynamic inactivation: an in vitro study

The purpose of this study was to evaluate specific effects of photodynamic inactivation (PDI) using methylene blue as photosensitizer and low-power laser irradiation on the viability of single-, dual-, and three-species biofilms formed by C. albicans, S. aureus, and S. mutans. Biofilms were grown in acrylic discs immersed in sterile brain heart infusion broth (BHI) containing 5% sucrose, inoculated with microbial suspension (10(6) cells/ml) and incubated for 5days. On the fifth day, the effects of the methylene blue (MB) photosensitizer at a concentration of 0.1mg/ml for 5min and InGaAlP laser (660nm) for 98s, alone and conjugated were evaluated. Next, the discs were placed in tubes with sterile physiological solution [0.9% sodium chloride (NaCl)] and sonicated for to disperse the biofilms. Ten-fold serial dilutions were carried and aliquots seeded in selective agar, which were then incubated for 48h. Then the numbers CFU/ml (log(10)) were counted and analyzed statistically (ANOVA, Tukey test, p < 0.05). Scanning electron microscopy (SEM) on discs treated with PDI and control biofilms groups was performed. Significant decreases in the viability of all microorganisms were observed for biofilms exposed to PDI mediated by MB dye. Reductions (log(10)) of single-species biofilms were greater (2.32-3.29) than the association of biofilms (1.00-2.44). Scanning electron microscopy micrographs suggested that lethal photosensitization occurred predominantly in the outermost layers of the biofilms. The results showed that PDI mediated by MB dye, might be a useful approach for the control of oral biofilms.

Photodynamic therapy: a targeted therapy in periodontics

The oral cavity is colonized by a large number and highly diversified communities of micro-organisms. Bacterial biofilm present on tooth or root surface is a major cause of gingivitis and periodontitis. Chemical antimicrobial agents are widely used in prophylactic and therapeutic regimens for dental plaque related diseases, which are among the most common human infections. As these agents are difficult to maintain at therapeutic concentrations in the oral cavity and can be rendered ineffective by resistance development in target organisms, there is a need for an alternative antimicrobial approach. A novel approach, photodynamic therapy (PDT), could be a solution to these problems. Lethal photosensitization of many bacteria, both Gram positive and Gram negative was found in many studies. The advantage of this new approach includes rapid bacterial elimination, minimal chance of resistance development and safety of adjacent host tissue and normal microflora. Thus, the available knowledge of photodynamic therapy should encourage a more clinically oriented application of this technique.

Photodynamic inactivation of wound-associated bacteria with new troponyl (pyro)pheophobides

In this study, the effect of light activated agent, methyl (pyro)pheophorbide-a, which bears non-aromatic cyclic compound, excited with red light from a LED on the viability of S. aureus, S. epidermidis, and E. coli was investigated. All species were susceptible to killing by photosensitization and photodynamic effect was dependent on both the chemical structure and concentration. However, E. coli was not susceptible to concentrations used to obtain a significant kill with the Gram-positive bacteria upon irradiation. To more closely mimic the conditions of wounds, photodynamic therapy was carried out on S. aureus, which is the most important organism that can cause a range of mild to severe infections in skin and burn wounds, in the presence of human blood plasma and human serum albumin, representing a wound fluid model. Results indicate that microorganisms could be successfully photoinactivated by tropolone methyl (pyro)pheophorbide-a derivatives when suspended in phosphate buffered saline. However, changing the medium into 4.5% and 7% HSA/PBS solutions reduced the effectiveness of lethal photosensitization of bacteria. The same results were obtained with human blood plasma. Also, the mechanism of bacterial cell inactivation by a sensitizer and light was studied with reactive oxygen species scavengers. Further evidence of the involvement of singlet oxygen is provided by the protective effect of the singlet oxygen scavenger, sodium azide.