Photodynamic Inactivation Of Microorganisms Research Articles

Refining antimicrobial photodynamic therapy: effect of charge distribution and central metal ion in fluorinated porphyrins on effective control of planktonic and biofilm bacterial forms

Antibiotic resistance represents a pressing global health challenge, now acknowledged as a critical concern within the framework of One Health. Photodynamic inactivation of microorganisms (PDI) offers an attractive, non-invasive approach known for its flexibility, independence from microbial resistance patterns, broad-spectrum efficacy, and minimal risk of inducing resistance. Various photosensitizers, including porphyrin derivatives have been explored for pathogen eradication. In this context, we present the synthesis, spectroscopic and photophysical characteristics as well as antimicrobial properties of a palladium(II)-porphyrin derivative (PdF2POH), along with its zinc(II)- and free-base counterparts (ZnF2POH and F2POH, respectively). Our findings reveal that the palladium(II)-porphyrin complex can be classified as an excellent generator of reactive oxygen species (ROS), encompassing both singlet oxygen (Φ△ = 0.93) and oxygen-centered radicals. The ability of photosensitizers to generate ROS was assessed using a variety of direct (luminescence measurements) and indirect techniques, including specific fluorescent probes both in solution and in microorganisms during the PDI procedure. We investigated the PDI efficacy of F2POH, ZnF2POH, and PdF2POH against both Gram-negative and Gram-positive bacteria. All tested compounds proved high activity against Gram-positive species, with PdF2POH exhibiting superior efficacy, leading to up to a 6-log reduction in S. aureus viability. Notably, PdF2POH-mediated PDI displayed remarkable effectiveness against S. aureus biofilm, a challenging target due to its complex structure and increased resistance to conventional treatments. Furthermore, our results show that PDI with PdF2POH is more selective for bacterial than for mammalian cells, particularly at lower light doses (up to 5 J/cm2 of blue light illumination). This enhanced efficacy of PdF2POH-mediated PDI as compared to ZnF2POH and F2POH can be attributed to more pronounced ROS generation by palladium derivative via both types of photochemical mechanisms (high yields of singlet oxygen generation as well as oxygen-centered radicals). Additionally, PDI proved effective in eliminating bacteria within S. aureus-infected human keratinocytes, inhibiting infection progression while preserving the viability and integrity of infected HaCaT cells. These findings underscore the potential of metalloporphyrins, particularly the Pd(II)-porphyrin complex, as promising photosensitizers for PDI in various bacterial infections, warranting further investigation in advanced infection models.Graphical abstract

Dihydroxyanthraquinones as stable and cost-effective TiO2 photosensitizers for environmental and biomedical applications

Materials based on titanium(IV) oxide and four dihydroxyanthraquinones were synthesized using a simple impregnation method. The dyes (1,2-, 1,4-, 1,5- and 1,8-dihydroxyanthraquinone) did not alter the physical properties of bare TiO2, but photosensitized it to visible light, up to 600 nm. The materials exhibit good photocatalytic activity in this spectral range. Adsorbed 1,5- and 1,8-dihydroxyanthraquinones revealed exceptional stability compared to previously described semiconductors modified with organic compounds. The spectroscopic characterization of the synthesized materials indicates that photosensitization occurs via an indirect electron transfer mechanism. To exploit their promising properties, appropriate tests were carried out towards the photodynamic inactivation of microorganisms. It was found that upon excitation with green light the tested photomaterials exhibited remarkable activity (3–4 log units) against Gram-negative and Gram-positive bacteria, as well as fungi. Moreover, the addition of inert potassium iodide to the photocatalytic system led to the complete eradication (>7 log units) of studied microorganisms. Elaborated materials appeared exceptionally photoactive under visible light, photostable, and cost-effective and therefore can be considered promising photocatalysts for environmental and biomedical applications.

Safranine-O Incorporated in F127 Nanocarriers Reduces the Contamination of Staphylococcus aureus in Sheep’s Milk

Mastitis caused by Staphylococcus aureus uses antibiotics as conventional treatment, a practice that has led to bacterial resistance. Therefore, the photodynamic inactivation of microorganisms (PDIM), has the advantage of inactivating pathogens without leading to the selection of resistant microorganisms. The objective of the study was to evaluate the antimicrobial activity of the photosensitizer (PS) Safranine-O (Sf), incorporated in the nanocarrier Pluronic® F127 against strains of S. aureus isolated from sheep milk. The reduction of contamination in experimentally contaminated milk and Muller Hilton Broth (MHB), the formation of microbial biofilm, and its effect as post dipping in the decrease of total mesophilic aerobic and Staphylococcal counts in milk were evaluated. Three strains of S. aureus (SO1, SO3, SO4) and a coagulase-negative Staphylococcus (CNS) strain (SO2) were identified through the nuc and coa genes and all were sensitive to PDIM. The minimum inhibitory concentration (MIC) ranged from 1.18 to 18.75 mg/mL in the different isolates. The SO4 strain was resistant to Ampicillin and Trimetropim. When the microorganisms were cultivated in milk and MHB, there was a reduction in staph counts by 97.33% and 99.63%, respectively. In stainless steel coupons, photoinactivation reduced S. aureus adhesion by up to 45.92% (milk) and 99.5% (MHB) (p<0.05). The photoactivated Sf was similar to commercial lactic acid when applied as a dipping powder. These results showed that Sf mediated PDIM effectively inactivated pathogens that cause mastitis and reduced milk contamination.

Photodynamic inactivation of microorganisms in different water matrices: The effect of physicochemical parameters on the treatment outcome

Wastewater (WW) insufficiently treated for the disinfection of microorganisms, including pathogenic ones, is a source of concern and a possible generator of public health problems. Traditional disinfection methods to reduce pathogens concentration (e.g., chlorination, ozonation, UV) are expensive, unsafe, and/or sometimes ineffective, highlighting the need for new disinfection technologies. The promising results of photodynamic inactivation (PDI) treatment to eradicate microorganisms suggest the efficacy of this treatment to improve WW quality. This work aimed to assess if PDI can be successfully extended to real contexts for the microbial inactivation in WW. For the first time, PDI experiments with 9 different water matrices compositions were performed to inquire about the influence of some of their physicochemical parameters on the effectiveness of microbial inactivation. Bacterial photoinactivation was tested in freshwater, aquaculture water, and seawater samples, as well as in influents and effluents samples from domestic, industrial, and a mixture of industrial and domestic WW receiving wastewater treatment plants (WWTPs). Additionally, PDI assays were performed in phosphate-buffered saline isotonic solution (PBS), used as an aqueous comparative matrix. To relate the PDI disinfection efficiency with the physicochemical compositions of the different used water matrices, a series of statistical analysis were performed, in order to support our main conclusions.Overall, the results showed that PDI is an effective and promising alternative to traditionally used WW disinfection methods, with a bacterial reduction of >3.0 log CFU/mL in all the water matrices within the first hour of PDI treatment, but also that the physicochemical composition of the aqueous matrices to be PDI-disinfected must be taken into account since they seem to influence the PDI efficacy, namely the pH, with acidic pH conditions seeming to be associated to a better PDI performance in general.

Photodynamic Polymers Constituted by Porphyrin Units as Antibacterial Materials

Photodynamic inactivation of microorganisms has emerged as a promising strategy to kill and eradicate pathogens. In this work, two polymers, TCP-P and ZnTCP-P, were synthesized by oxidative polymerization of 5,10,15,20-tetrakis [3-(N-ethylcarbazoyl)]porphyrin and its complex with Zn(II). Solid polymers consist of rods (diameter 100 nm, length ~100–500 nm) that form microporous structures on a surface. UV-visible absorption spectra in solution showed the Soret and Q bands characteristic of the corresponding constitutional porphyrins. In addition, the polymers presented two red emission bands with quantum yields ΦF = 0.11 for TCP-P and ΦF = 0.050 for ZnTCP-P. These compounds sensitized the production of singlet molecular oxygen with quantum yields of ΦΔ~0.3. Thus, the spectroscopic and photodynamic properties of the porphyrin units were maintained in the conjugates. The photodynamic activity induced by both polymers was tested to inactivate S. aureus. In cell suspensions, TCP-P was more effective than ZnTCP-P in killing bacteria. Viable S. aureus cells were not detected using 4 µM TCP-P after 20 min of irradiation. Moreover, both polymers showed a high photocytotoxic activity to eradicate S. aureus cells attached to a surface. The results indicate that these conjugated polymers can act as effective antimicrobial agents to photoinactivate pathogens.

Water soluble octa-imidazolium zinc phthalocyanine for nucleus/nucleolus cell fluorescence microscopy and photodynamic therapy.

A poly-cationic theranostic macrocycle was developed to perform confocal microscopy imaging and photodynamic therapy studies on a model of melanoma cancer, one of the most aggressive cancer. Hence, an octa-imidazolium zinc phthalocyanine was conveniently synthesized in large amount in three steps in a 44% overall yield: upon double nucleophilic aromatic substitution, cyclo-tetramerization and quaternization reactions. Such an octa-cationic molecule was readily soluble in physiological media, reaching concentrations beyond 1mM. It showed fluorescence properties in aqueous medium (ΦF = 0.31) with no noticeable aggregation, spectroscopy studies showed. In vitro confocal fluorescence microscopy studies carried out on murine melanoma model (B16F10 cells) showed that the fluorophore was mainly located in the cell nucleolus, an organelle of interest for the treatment of cancer. The anticancer photodynamic potential of the octa-cationic photosensitizer could be measured (IC50 = 5.4µM) using the MTS viability assay. Both fluorescence microscopy studies and photodynamic studies demonstrate the octa-cationic molecule is theranostic and could be further developed for future photodynamic diagnosis (PDD) and photodynamic inactivation of micro-organisms (PDI).

Porphycenes as broad-spectrum antimicrobial photosensitizers. Potentiation with potassium iodide

Two novel meso-tetrasubstituted porphycenes (Pc-Cbz and Pc-NEt2) have been synthesized by palladium-catalyzed Suzuki cross-coupling reactions over 9,10,19,20-tetrakis(4-iodophenyl)porphycene. Pc-Cbz contains four carbazole groups on the periphery of the tetrapyrrolic macrocycle. Instead, Pc-NEt2 presents four basic tertiary amine substituents, which can be protonated at physiological pH, acquiring four positive charges. Both photosensitizers (PSs) were designed to evaluate the effect of different substitution patterns on the photodynamic inactivation of microorganisms. Their absorption and fluorescence properties were almost unmodified regardless of the substituent groups on the periphery. The characteristic red emission makes them promising fluorescent probes for cell imaging. Moreover, both macrocycles were able to generate reactive oxygen species by both photodynamic mechanisms under aerobic light irradiation. The photokilling action of these PSs was assessed in vitro against Candida albicans (yeast), Staphylococcus aureus (Gram-positive bacterium), and Escherichia coli (Gram-negative bacterium). Our results demonstrate that the peripheral substitution significantly affected the photoinactivation performance. Thus, Pc-NEt2 was more effective than Pc-Cbz in killing microorganisms using lower concentrations and shorter irradiation periods, evidencing that external substitution is a main structural feature. Also, the photoinactivation efficiency mediated by these porphycenes was potentiated by adding KI. Under these conditions, a complete eradication of all pathogenic microorganisms was obtained by combining Pc-NEt2 and KI. Therefore, Pc-NEt2 can be used as an effective broad-spectrum antimicrobial PS. Accordingly, this work stands out as a promising starting point for the design of new porphycene-based PSs for photodynamic inactivation (PDI) of microorganisms. Our outcomes also disclose that the combination of these PSs with KI is an important factor in order to improve the PDI treatments and the current antimicrobial therapies.

Photodynamic Inactivation of Microorganisms Using Semisynthetic Chlorophyll a Derivatives as Photosensitizers.

In this study, we describe the semisynthesis of cost-effective photosensitizers (PSs) derived from chlorophyll a containing different substituents and using previously described methods from the literature. We compared their structures when used in photodynamic inactivation (PDI) against Staphylococcus aureus, Escherichia coli, and Candida albicans under different conditions. The PSs containing carboxylic acids and butyl groups were highly effective against S. aureus and C. albicans following our PDI protocol. Overall, our results indicate that these nature-inspired PSs are a promising alternative to selectively inactivate microorganisms using PDI.

Edible coatings and application of photodynamics in ricotta cheese preservation

The present study evaluated the efficiency of an edible coating of alginate and erythrosine in the preservation of ricotta cheese submitted to the technique of Photodynamic Inactivation of Microorganisms (PDIM). Three treatments were evaluated: samples of cheese coated with alginate solution, with alginate solution and 10 μmol/L erythrosine and with 100 μmol/L erythrosine. Mechanical properties, water vapor sorption, solubility and permeability and the release of erythrosine in aqueous medium were characterized. The antimicrobial effect of the coatings followed by photodynamic application was evaluated during cheese storage for 21 days. The coated cheese samples were physico-chemically analysed during 21 days of storage. Salmonella and S. aureus were not detected in any cheese samples, but a 1 log cycle reduction in the Coliform count was only observed when 100 μmol/L erythrosine was used. The PDMI technique did not induce lipid oxidation in cheese samples. The presence of 100 μmol/L reduced tensile strength by 25% at rupture. The water solubility and water vapor permeability of the roofs were not affected by the addition of erythrosine. The application of edible coatings in combination with PDIM is a good alternative to extend the shelf life of ricotta cheese without compromising sensory attributes and nutritional characteristics.

Inhibitory effects of calcium or magnesium ions on PDI

Photodynamic inactivation of microorganisms (PDI) finds use in a variety of applications. Several studies report on substances enhancing or inhibiting PDI. In this study, we analyzed the inhibitory potential of ubiquitous salts like CaCl2 and MgCl2 on PDI against Staphylococcus aureus and Pseudomonas aeruginosa cells using five cationic photosensitizers methylene blue, TMPyP, SAPYR, FLASH-02a and FLASH-06a.TMPyP changed its molecular structure when exposed to MgCl2, most likely due to complexation. CaCl2 substantially affected singlet oxygen generation by MB at small concentrations. Elevated concentrations of CaCl2 and MgCl2 impaired PDI up to a total loss of bacterial reduction, whereas CaCl2 is more detrimental for PDI than MgCl2. Binding assays cannot not explain the differences of PDI efficacy. It is assumed that divalent ions tightly bind to bacterial cells hindering close binding of the photosensitizers to the membranes. Consequently, photosensitizer binding might be shifted to outer compartments like teichoic acids in Gram-positives or outer sugar moieties of the LPS in Gram-negatives, attenuating the oxidative damage of susceptible cellular structures.In conclusion, CaCl2 and MgCl2 have an inhibitory potential at different phases in PDI. These effects should be considered when using PDI in an environment that contains such salts like in tap water or different fields of food industry.

Antimicrobial photoinactivation approach based on Safranine-O loaded F127 copolymeric micelles for control of gram-negative and gram-positive bacteria

The present study aims to evaluate the photodynamic efficiency of Safranine-O (Sf) in the inactivation of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923). Sf cytotoxicity activities were evaluated against L929 fibroblasts, J774A.1 macrophages, and LLCMK2 cells (monkey [Macaca mulatta] kidney epithelial cells) by tetrazolium salt assays (MTT). Photodynamic therapy (PDT) is a therapeutic modality that has shown effectiveness in the inactivation of microorganisms. Sf-mediated photodynamic inactivation of microorganisms (PDIM) was performed at different concentrations of the photosensitizer (PS) with a minimum inhibitory concentration (MIC) of 9.4 μg mL−1 for the two bacteria evaluated and a minimum bactericidal concentration (MBC) of 9.4 μg mL−1 for E. coli and 37.5 μg mL−1 for S. aureus. The bacteria viability was analyzed by flow cytometry through staining with propidium iodide (PI). The population of 10,000 bacteria (E. coli or S. aureus) treated with PDIM showed cell mortality of 21.5% and 30.48%, respectively. The morphological analysis of the pathogens allowed the investigation of cell damage involved with PDIM by scanning electron microscopy (SEM) and transmission (MET). Sf-mediated PDT proved to be efficient with severe photodamage and effective inactivation of Gram negative and Gram-positive bacteria.

Meso-substituted cationic 3- and 4-N-Pyridylporphyrins and their Zn(II) derivatives for antibacterial photodynamic therapy

Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn[Formula: see text] and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Photodynamic inactivation of Pseudomonas fluorescens in Minas Frescal cheese using curcumin as a photosensitizer

The dairy industries demand innovative technologies for food preservation and elimination of psychrotrophic bacteria like the Photodynamic Inactivation of Microorganisms (PDIM) modalit, which is based on the generation of reactive oxygen species using photosensitizers. The objective was to determine in vitro the phototoxic potential of Curcumin (CUR) solubilized in different media against Pseudomonas fluorescens. In Minas Frescal cheese inoculated with Pseudomonas fluorescens, CUR acted as an antimicrobial agent and photosensitizers when incorporated in an edible and biodegradable coating. The coatings were characterized in terms of mechanical properties and permeability. The cheeses were evaluated on days 0, 3, 6, 9 and 12 by microbiological, physical-chemical and mechanical analysis. The efficiency of PDIM was influenced by solubilizers and concentrations of CUR, observing the synergistic effect of CUR with irradiation. Dimethyl sulfoxide and ethanol were the solubilizers that allowed greater CUR phototoxic activity and reduced 7 log CFU/mL of Pseudomonas fluorescens, the main spoilage bacteria in milk and dairy products. In cheeses, the photoinhibition of microorganisms was hampered by the complexity of the surface. The samples treated with CUR showed lower bacterial count and proteolysis, and consequently, greater hardness. Therefore, PDIM can be an alternative technique for use in dairy products.

Design of Photosensitizing Agents for Targeted Antimicrobial Photodynamic Therapy.

Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O2−, type-I mechanism) or singlet oxygen (1O2*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT.

Methods to Unravel Pathways of Reactive Oxygen Species in the Photodynamic Inactivation of Bacteria.

Different experimental conditions can be used to detect the presence of reactive oxygen species (ROS) in the photodynamic inactivation of microorganisms. Here, we describe the effect of the media and the addition of ROS scavengers to obtain insight about the oxidative processes that take place during the photokilling of bacteria. In addition, 9,10-dimethylanthracene was used to sense the generation of singlet molecular oxygen, O2(1Δg), in microbial cells. Thus, the contribution of type I or type II pathways in the photocytotoxicity action can be rapidly detected and compared between different photosensitizers.

Diketopyrrolopyrrole-fullerene C60 architectures as highly efficient heavy atom-free photosensitizers: synthesis, photophysical properties and photodynamic activity.

Chromophore-fullerene C60 hybrids possess interesting properties that enable them to act as heavy atom-free photosensitizers and reactive oxygen species (ROS) producers. Here, two new diketopyrrolopyrrole-C60 conjugates were efficiently synthesized and characterized. The conjugates show broadband absorption in the visible spectral region, in which diketopyrrolopyrrole dyes act as light-harvesting antenna with very high capacity to populate excited triplet states. Furthermore, the ability of diketopyrrolopyrrole-C60 systems to generate singlet molecular oxygen was explored for the first time in solvents of different polarities. The experimental results show that these architectures exhibit very high production rates of this ROS. In addition, a preliminary study on Staphylococcus aureus cell suspensions indicates that both conjugates exhibit phototoxicity after irradiation with green LED light. Thus, the data obtained provide evidence that these diketopyrrolopyrrole-C60 architectures act as potential heavy atom-free photosensitizers in photodynamic inactivation of microorganisms and other singlet oxygen-mediated applications.

In the Right Light: Photodynamic Inactivation of Microorganisms Using a LED-Based Illumination Device Tailored for the Antimicrobial Application

Drug-resistant bacteria threaten the health of people world-wide and cause high costs to their health systems. According to Scientific American, the number of regrettable fatalities due to the bacteria that are resistant to conventional antibiotics will sum up to 300 million until 2050 if the problem is not tackled immediately. Photodynamic Inactivation (PDI) has proven effective against microorganisms irrespective of their resistance to conventional treatment, but for the translation into clinical practice, economic, homogenous and powerful light sources holding approval as medical devices are needed. In this study we present two novel light emitting diode (LED)-based lamps (Repuls7PDI-red and Repuls7PDI-blue) tailored for application in PDI and demonstrate their photodynamic efficiency upon using either methylene blue (MB), a photoactive compound widely used in PDI, or Sodium Magnesium Chlorophyllin (CHL), a water-soluble derivative of chlorophyll, which holds approval as food additive E140, against bacteria and fungi. Gram+ Staphylococcus aureus, Gram− Escherichia coli and the yeast Candida albicans serve as model systems. Repuls7PDI-red emits a wavelength of 635 nm and an intensity of 27.6 ± 2.4 mW·cm−2 at a distance of 13.5 cm between the light source and the target, while the Repuls7PDI-blue allows an exposure at 433 nm (within the range of violet light) (6.4 ± 0.5 mW·cm−2 at 13.5 cm). Methylene blue was photoactivated with the Repuls7PDI-red at 635 nm (25.6 J·cm−2) and allows for photokilling of E. coli by more than 6 log10 steps at a concentration of 10 µM MB. Using equal parameters, more than 99.99999% of S. aureus (20 µM MB) and 99.99% of C. albicans (50 µM MB) were killed. If blue light (Repuls7PDI-blue, 433 nm, 6.6 J·cm2) is used to trigger the production of reactive oxygen species (ROS), a photoinactivation of S. aureus (5 µM CHL, CFU reduction > 7 log10) and C. albicans (>7 log10) below the detection limit is achieved. PDI based on CHL (10 µM) using red light activation reduces the number of viable S. aureus by more than 6 log10. Our data prove that both LED-based light sources are applicable for Photodynamic Inactivation. Their easy-to-use concept, high light output and well-defined wavelength might facilitate the translation of PDI into clinical practice.

Surface Modification of Nanocrystalline TiO2 Materials with Sulfonated Porphyrins for Visible Light Antimicrobial Therapy

Highly-active, surface-modified anatase TiO2 nanoparticles were successfully synthesized and characterized. The morphological and optical properties of the obtained (metallo)porphyrin@qTiO2 materials were evaluated using absorption and fluorescence spectroscopy, scanning electron microscopy (SEM) imaging, and dynamic light scattering (DLS). These hybrid nanoparticles efficiently generated reactive oxygen species (ROS) under blue-light irradiation (420 ± 20 nm) and possessed a unimodal size distribution of 20–70 nm in diameter. The antimicrobial performance of the synthetized agents was examined against Gram-negative and Gram-positive bacteria. After a short-term incubation of microorganisms with nanomaterials (at 1 g/L) and irradiation with blue-light at a dose of 10 J/cm2, 2–3 logs of Escherichia coli, and 3–4 logs of Staphylococcus aureus were inactivated. A further decrease in bacteria viability was observed after potentiation photodynamic inactivation (PDI), either by H2O2 or KI, resulting in complete microorganism eradication even when using low material concentration (from 0.1 g/L). SEM analysis of bacteria morphology after each mode of PDI suggested different mechanisms of cellular disruption depending on the type of generated oxygen and/or iodide species. These data suggest that TiO2-based materials modified with sulfonated porphyrins are efficient photocatalysts that could be successfully used in biomedical strategies, most notably, photodynamic inactivation of microorganisms.

From Protohypericin to Hypericin: Photoconversion Analysis Using a Time-Resolved Thermal Lens Technique.

Hypericin (Hyp) is a natural compound with interesting photophysical and pharmacological properties, which has been used in photodynamic therapy and photodynamic inactivation of microorganisms. Its synthesis is based on a series of chemical processes that ends with a light-drug interaction by the photoconversion of protohypericin (pHyp) to Hyp. Although this photosensitizer is used in a variety of medical applications, the photophysical and photochemical mechanisms involved in the final step related to the photo production of Hyp are not completely understood at the molecular level. Protohypericin concentration, solvents, light irradiation under different wavelengths, and a sort of variables could play an important role in predicting the yielding of this photoconversion process. Here, we used the high-sensitive and remote measurement characteristics of the time-resolved thermal lens technique to investigate the relation between the light-induced photoconversion rate of pHyp to Hyp and the initial concentration pHyp. The results show a linear dependence of the photoreaction rate with the concentration of pHyp, indicating that the overall reaction process includes steps comprising the formation of distinct intermediate species. We demonstrate the applicability of the thermal lens technique for the photochemical characterization of photosensitive drugs at low concentration levels.

Development and applications of safranine-loaded Pluronic® F127 and P123 photoactive nanocarriers for prevention of bovine mastitis: In vitro and in vivo studies

Photodynamic therapy (PDT) is a therapeutic modality that exploits the formation of singlet oxygen through a photosensitizing compound. This compound is capable of eradicating sick cells or several strains of microorganisms. Its main advantage is associated with high selectivity and ability to avoid the self-resistance of pathogens, as often expected after the prolonged use of conventional antibiotics. These characteristics made it possible to the explore the performance of Safranine-O (Sf) photosensitizer incorporated in F127 and P123 Pluronic® 4% (w/v) as nanocarriers solubilizer in the Photodynamic Inactivation of Microorganisms (PDIM) for post-dipping procedures in the prevention of bovine mastitis. Spectroscopic studies have shown the effective monomerization of Sf after being loaded into nanostructured micellar systems. The Sf-F127 and Sf-P123 showed bond molar absorptivity coefficients (ɛ) in the order of 103 L mol−1 and preferential relative locations in the hydrophilic hydrated micelle region (shell), as verified through the high Stern-Volmer constants (11.4 for Sf-F127 and 7.3 for Sf-P123) and proximity between apparent pKa (pKaap) values (Sf-F127 ∼ Sf-P123) with a pKa of Sf in water. Sf singlet oxygen quantum yield in water was 0.24. This was determined by the indirect method of photodegradation of the chemical probe tryptophan. In vitro studies of the Sf-F127 and Sf-P123 systems proved to be efficient in inactivating the bacteria that cause bovine mastitis. In vivo evaluations in Dutch dairy cows demonstrated the viability of the system as a form of treatment or prevention of bovine mastitis in post-dipping procedures.