Photoinactivation effect of eosin methylene blue and chlorophyllin sodium-copper against Staphylococcus aureus and Escherichia coli

Photoinactivation of Multidrug-Resistant mcr-1-Positive E. coli Using PCPDTBT Conjugated Polymer Nanoparticles under White Light

The issue of antimicrobial resistance is an escalating concern within the scope of global health. It is predicted that the existence of antibiotic-resistant bacteria might result in an estimated annual death of up to 10 million by 2050, along with possible economic losses ranging from 100 to 210 trillion. This study reports the production of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] nanoparticles (PCPDTBT-NPs) by nanoprecipitation as an alternative to tackle this problem. The size, shape, and optical features of these conjugated polymer NPs were analyzed. Their efficacy as photosensitizers against nonresistant (ATCC) and multidrug-resistant mcr-1-positive Escherichia coli was assessed under white light doses of 250 and 375 J·cm-2. PCPDTBT-NPs inactivated both E. coli strains exposed to white light at an intensity of 375 J·cm-2, while no antimicrobial effect was observed in the group not exposed to white light. Reactive oxygen species and singlet oxygen were detected using DCFH-DA and DPBF probes, allowing the investigation of the photoinactivation pathways. This work showcases PCPDTBT-NPs as photosensitizers to eliminate multidrug-resistant bacteria through photodynamic inactivation employing visible light.

Dextran-Based Antibacterial Hydrogel Dressings for Accelerating Infected Wound Healing by Reducing Inflammation Levels

Infected wounds pose challenges such as exudate management, bacterial infections, and persistent inflammation, making them a significant challenge for modern dressings. To address these issues in infected wounds more effectively, aerogel-hydrogel biphase gels based on dextran are developed. The gel introduced in this study exhibits antibacterial and anti-inflammatory properties in the process of wound therapy, contributing to accelerated wound healing. The aerogel phase exhibits exceptional water-absorption capabilities, rapidly soaking up exudate from infected wound, thereby fostering a clean and hygienic wound healing microenvironment. Concurrently, the aerogel phase is enriched with hydrogen sulfide donors. Following water absorption and the formation of the hydrogel phase, it enables the sustained release of hydrogen sulfide around the wound sites. The experiments confirm that hydrogen sulfide, by promoting M2 macrophage differentiation and reducing the levels of inflammatory factors, effectively diminishes local inflammation levels at the wound site. Furthermore, the sodium copper chlorophyllin component within the hydrogel phase demonstrates effective antibacterial properties through photodynamic antimicrobial therapy, providing a viable solution to wound infection challenges.

Evaluation of visible light and natural photosensitizers against Staphylococcus epidermidis and Staphylococcus saprophyticus planktonic cells and biofilm

Antimicrobial photoinactivation (API) has shown some promise in potentially treating different nosocomial bacterial infections, however, its application on staphylococci, especially other than Staphylococcus aureus or methicillin-resistant S. aureus (MRSA) species is still limited. Although S. aureus is a well-known and important nosocomial pathogen, several other species of the genus, particularly coagulase-negative Staphylococcus (CNS) species such as Staphylococcus epidermidis and Staphylococcus saprophyticus, can also cause healthcare-associated infections and foodborne intoxications. CNS are often involved in resilient biofilm formation on medical devices and can cause infections in patients with compromised immune systems or those undergoing invasive procedures. In this study, the effects of chlorophyllin and riboflavin-mediated API on S. epidermidis and S. saprophyticus planktonic cells and biofilm are demonstrated for the first time. Based on the residual growth determination and metabolic reduction ability changes, higher inactivating efficiency of chlorophyllin-mediated API was determined against the planktonic cells of both tested species of bacteria and against S. saprophyticus biofilm. Some insights on whether aqueous solutions of riboflavin and chlorophyllin, when illuminated with optimal exciting wavelength (440 nm and 402 nm, respectively) generate O2-•, are also provided in this work.

Photodynamic inactivation of methicillin-resistant Staphylococcus aureus by using Giemsa dye as a photosensitizer

The rise of antibiotic-resistant bacteria calls for innovative approaches to combat multidrug-resistant strains. Here, the potential of the standard histological stain, Giemsa, to act as a photosensitizer (PS) for antimicrobial photodynamic inactivation (aPDI) against methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) strains is reported. Bioassays were performed using various Giemsa concentrations (ranging from 0.0 to 20.0 µM) under 625 nm illumination at a light dose of 30 J cm-2. Remarkably, Giemsa completely inhibited the growth of MSSA and MRSA bacterial colonies for concentrations at 10 µM and higher but exhibited no inhibitory effect without light exposure. Partition coefficient analysis revealed Giemsa's affinity for membranes. Furthermore, we quantified the production of reactive oxygen species (ROS) and singlet oxygen (1O2) to elucidate the aPDI mechanisms underlying bacterial inactivation mediated by Giemsa. These findings highlight Giemsa stain's potential as a PS in aPDI for targeting multidrug-resistant bacteria.

Chlorophyllin-Containing Copolymers and Their Responsive Properties

Copper-chlorophyllin is a water-soluble derivative of chlorophylls and shows low cytotoxicity and antimutagenic properties in cultured cells. It has multiple applications, including its use as a photosensitizer in photothermal therapy because of its green light-activated photothermal performance. In this work, it was copolymerized with a poly(ethylene glycol) methacrylic monomer to yield random copolymers by free radical polymerization, which showed dual temperature- and pH-dependent phase transitions in aqueous solutions. The cloud points of the copolymer solutions were raised by lowering the pH of the aqueous solutions due to the protonation of the carboxylic groups on the chlorophyllin moieties, which decreased the overall hydrophilicity of the polymers. At low pH values, complete protonation of the carboxylic acid groups of the chlorophyllin moieties led to an irreversible aggregation of the copolymers in water. The incorporation of chlorophyllin in the copolymer improved its stability over its single molecular form.

Evaluation of a novel water-soluble decanoic acid formulation as a fruit sanitizer

Fruits irrigated with contaminated water can transmit various pathogens. High sugar content in fruits such as black cherry (BC) fruit encourages microbial proliferation. A novel water-soluble decanoic acid (WSDA) was evaluated as a fruit sanitizer and compared with other traditional fruit sanitizers such as ethanol, bleach, or dishwasher surfactants. WSDA sanitizer killed yeasts, molds and bacteria including E. coli microbes effectively as other sanitizers with (4 log cycle reduction) of microbial load. Furthermore, the bacterial sanitization mechanism i.e. bactericidal or bacteriostatic was evaluated for alcohol, bleaching and WASDA solutions. E. coli was selected as the model pathogen used for such comparison. Results indicated that the mechanism of action for the three sanitizer solutions against E. coli was bactericidal. The problem with most used fruit sanitizers is their negative influence on fruit quality in terms of physical, mechanical and taste properties. In addition, some led to toxicological and ecological concerns. Thus, studies were conducted to explore the changes in the exocarp cell structure of BC fruit upon exposure to WSDA and other sanitizers using microscopic investigation. WSDA could have a very mild or gentle effect on the BC fruit cells compared to other sanitizers. Alcohol, bleaching and dishwasher surfactant changed the cellular structures and the intercellular spaces. Sanitizers may also affect fruit swelling. WSDA showed an increase in percent weight gain but it was significantly (p < 0.05) much lower than dishwasher surfactant and bleaching solution. BC Fruit flesh firmness and hardness were investigated upon exposure to different sanitizer solutions. BC fruit treated with WSDA showed the highest firmness values. Some liquid sanitizers could affect fruit quality in terms of fruit taste. Sensory evaluation in terms of the sanitizer's smell, texture and hedonic of BC fruit after soaking in different sanitizers was carried out. All sensory parameters of BC fruit soaked with WSDA were similar with insignificant differences (p > 0.05) compared to BC fruit soaked in tap water. However, the sensory parameters were significantly different (p < 0.05) when compared with alcohol, bleach and dishwasher surfactant. This ensures that WSDA was superior to other evaluated sanitizers in terms of physical, mechanical and fruit quality.

Effectiveness of purple led for inactivation of Bacillus subtilis and Escherichia coli bacteria in in vitro sterilizers

Bacteria are inactivated using a technique called photodynamic inactivation, which combines light with a photosensitizer with the right spectrum. The objective of this study is to ascertain the e­ciency of purple LEDs for photoinactivating Bacillus subtilis and Escherichia coli bacteria as well as the ideal purple LED exposure energy density. This study technique involves exposing bacteria to purple LED radiation. Two elements of variation are used during irradiation. The first variation is the illumination variation at distances of 3 cm, 6 cm, 9 cm, and 12 cm. The second variation involves changing the amount of radiation for 30, 60, 90, and 120 minutes. The Total Plate Count (TPC) method was used to count the number of colonies. Statistical tests were utilized in data analysis, namely the One Way Anova test (analysis of variance). The results of this study indicated that 395 nm purple LED irradiation caused a decrease in Log CFU/mL of Bacillus subtilis and Escherichia coli bacteria. Inactivation of Bacillus subtilis bacteria showed a higher mortality percentage than Escherichia coli bacteria. Changes in other irradiation distances also showed a higher percentage of death for Bacillus subtilis bacteria than Escherichia coli bacteria. The highest percentage of death was 98.5% for Bacillus subtilis bacteria and 94.3% for Escherichia coli bacteria at position C with an irradiation distance of 3 cm and an energy density of 524 J/cm2 with an LED exposure time of 120 minutes. This shows that the percentage of death of bacteria Bacillus subtilis and Escherichia coli increased with increasing doses of LED energy with the greatest percentage of death in Gram-positive bacteria Bacillus subtilis.

Polyethylenimine Increases Antibacterial Efficiency of Chlorophyllin

Polyethylenimines (PEIs), a group of polycationic molecules, are known to impair the outer membrane of Gram-negative bacteria and exhibit antimicrobial activity. The outer membrane of Gram-negative strains hinders the uptake of photosensitizer chlorophyllin. In this study, we report chlorophyllin and branched PEI combinations’ activity against Escherichia coli strains DH5α and RB791, Salmonella enterica sv. Typhimurium LT2, and Bacillus subtilis 168. The minimal bactericidal concentration (MBC) was determined by plating cells treated with different concentrations of PEI and chlorophyllin on agar and monitoring their growth after 24 h. All tested combinations of PEI and chlorophyllin were lethal for S. enterica after 240 min of incubation in light, whereas PEI alone (<100 µg mL−1) was ineffective. In the darkness, complete inhibition was noted with a combination of ≥2.5 µg mL−1 chlorophyllin and 50 µg mL−1 PEI. If applied alone, PEI alone of ≥800 µg mL−1 of PEI was required to completely inactivate E. coli DH5α cells in light, whereas with ≥5 µg mL−1 chlorophyllin, only ≥100 µg mL−1 PEI was needed. No effect was detected in darkness with PEI alone. However, 1600 µg mL−1 PEI in combination with 2.5 µg mL−1 resulted in complete inactivation after 4 h dark incubation. PEI alone did not inhibit E. coli strain RB791, while cells were inactivated when treated with 10 µg mL−1 chlorophyllin in combination with ≥100 µg mL−1 (in light) or ≥800 µg mL−1 PEI (in darkness). Under illumination, B. subtilis was inactivated at all tested concentrations. In the darkness, 1 µg mL−1 chlorophyllin and 12.5 µg mL−1 PEI were lethal for B. subtilis. Overall, PEI can be used as an antimicrobial agent or potentiating agent for ameliorating the antimicrobial activity of chlorophyllin.

Sodium copper chlorophyll mediated photodynamic treatment inactivates Escherichia coli via oxidative damage

Photodynamic technology (PDT) is an emerging non-thermal processing technique, however, due to a lack of edible photosensitizers, its application to the food industry is limited. To better understand sodium copper chlorophyll (SCC) feasibility as a photosensitizer, we analyzed the effects of PDT-SCC on Escherichia coli O157:H7 inactivation using different lighting times (15, 30, 45, 60, and 75 min), lighting power (30, 60, 90, 120, and 150 W), and SCC concentrations (2, 4, 6, 8, and 10 mM). We showed that bactericidal effects depended on all three parameters, but the most suitable sterilization condition for E. coli occurred at 10 mM SCC, for 60 min at 120 W. We also investigated cell morphology, reactive oxygen species (ROS) production, the activity of three oxidative response enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)), and ompA, ompF, uvrA, and recA expression. When compared with the control group, PDT-SCC destroyed bacterial morphology, increased ROS production, decreased antioxidant enzyme activity (SOD, CAT, and GPX), down-regulated membrane protein gene expression, including ompA and ompF, and up-regulated the DNA damage-repair related genes, uvrA and recA. Thus, bacterial rupture caused by oxidative damage could be the main mechanism underpinning PDT-SCC action.

Biological properties of novel mono and double-decker hexadeca-substituted metal phthalocyanines

This study reports chemical agents that exhibit efficient antibacterial photodynamic, antimicrobial, antioxidant, biofilm inhibition, and DNA cleavage activities.

Photophysicochemical, sonochemical, and biological properties of novel hexadeca-substituted phthalocyanines bearing fluorinated groups

This study presents the preparation of a novel tetra-substituted phthalonitrile (1), namely, 3,6-bis(hexyloxy)-4,5-bis(4-(trifluoromethoxy)phenoxy)phthalonitrile (1) and its metal-free (2)/metal {M = Zn (3), Cu (4), Co (5), Lu(CH₃COO) (6), Lu (7)} phthalocyanines. A series of various spectroscopic methods (UV-vis, FT-IR, mass, and ¹H NMR spectroscopy) were performed for the characterization of the newly synthesized compounds. The potential of compounds 2, 3, and 6 as photosensitizing materials for photodynamic and sonophotodynamic therapies was evaluated by photophysical, photochemical, and sonochemical methods. The highest singlet quantum yields were obtained for the zinc phthalocyanine derivative 3 by performing photochemical and sonochemical methods. In addition, several biological activities of the new compounds 1-7 were investigated. The newly synthesized phthalocyanines exhibited excellent DPPH scavenging activity and also DNA nuclease activity. The antimicrobial activity of the new compounds was evaluated by the disc diffusion assay. Effective microbial cell viability inhibition was observed with phthalocyanine macromolecules. The photodynamic antimicrobial therapy of the phthalocyanines showed 100% bacterial inhibition when compared to the control. They also exhibited significant biofilm inhibition activity against S. aureus and P. aeruginosa. These results indicate that new phthalocyanines are promising photodynamic antimicrobial therapies for the treatment of infectious diseases.

Visible Light-Induced Antibacterial Activity of Pigments Extracted from Dregs of Green and Black Teas

Chlorophyll and its derivatives are potential natural sensitizers frequently applied in antimicrobial photodynamic therapy. Chlorophyll derivatives are formed naturally during tea processing, but they do not contribute to the color of tea infusions and thus are presumably left in the tea dregs. The present study aimed to investigate (i) the chlorophyll remnants in the pigments recovered from dregs of green and black teas and (ii) the antibacterial activity of pigments extracted from the tea dregs upon illumination using a light-emitting diode (LED) as the light source. Pigment analysis using high-performance liquid chromatography (HPLC) revealed the presence of main degradation products of chlorophylls, such as pheophytin and its epimers, pyropheophytin, and pheophorbides. In vitro assays demonstrated significant reductions in the number of viable bacteria in the presence of the pigments after 30 min of incubation with LED light irradiation. The descending order of bacterial susceptibility was Listeria monocytogenes > Staphylococcus aureus > Escherichia coli > Salmonella typhi. At an equivalent irradiation intensity, the blue and red LEDs could stimulate a comparable inactivation effect through photodynamic reactions. These findings demonstrated the valorization potential of tea dregs as a source of chlorophyll derivatives with visible light-induced antibacterial activity.

Photodynamic Inactivation of Methicillin-Resistant Staphylococcus aureus by a Natural Food Colorant (E-141ii)

This study evaluates the photosensitizing effectiveness of sodium copper chlorophyllin, a natural green colorant commonly used as a food additive (E-141ii), to inactivate methicillin-sensitive and methicillin-resistant Staphylococcus aureus under red-light illumination. Antimicrobial photodynamic inactivation (aPDI) was tested on a methicillin-sensitive reference strain (ATCC 25923) and a methicillin-resistant Staphylococcus aureus strain (GenBank accession number Mh087437) isolated from a clinical sample. The photoinactivation efficacy was investigated by exposing the bacterial strains to different E-141ii concentrations (0.0, 1.0, 2.5, 5.0, 10.0, and 20.0 µM) and to red light (625 nm) at 30 J cm⁻². The results showed that E-141ii itself did not prevent bacterial growth for all tested concentrations when cultures were placed in the dark. By contrast, E-141ii photoinactivated both methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) under red-light illumination. However, different dose responses were observed for MSSA and MRSA. Whilst the MSSA growth was inhibited to the detection limit of the method with E-141ii at 2.5 µM, >10 µM concentrations were required to inhibit the growth of MRSA. The data also suggest that E-141ii can produce reactive oxygen species (ROS) via Type I reaction by electron transfer from its first excited singlet state to oxygen molecules. Our findings demonstrate that the tested food colorant has great potential to be used in aPDI of MRSA.

Antimicrobial Photoinactivation Approach Based on Natural Agents for Control of Bacteria Biofilms in Spacecraft

A spacecraft is a confined system that is inhabited by a changing microbial consortium, mostly originating from life-supporting devices, equipment collected in pre-flight conditions, and crewmembers. Continuous monitoring of the spacecraft’s bioburden employing culture-based and molecular methods has shown the prevalence of various taxa, with human skin-associated microorganisms making a substantial contribution to the spacecraft microbiome. Microorganisms in spacecraft can prosper not only in planktonic growth mode but can also form more resilient biofilms that pose a higher risk to crewmembers’ health and the material integrity of the spacecraft’s equipment. Moreover, bacterial biofilms in space conditions are characterized by faster formation and acquisition of resistance to chemical and physical effects than under the same conditions on Earth, making most decontamination methods unsafe. There is currently no reported method available to combat biofilm formation in space effectively and safely. However, antibacterial photodynamic inactivation based on natural photosensitizers, which is reviewed in this work, seems to be a promising method.

The Effect of Antimicrobial Photodynamic Therapy Using Chlorophyllin–Phycocyanin Mixture on Enterococcus faecalis: The Influence of Different Light Sources

The purpose of this study was to evaluate the in vitro effect of the chlorophyllin–phycocyanin mixture (Photoactive+) as a photosensitizer (PS) during antimicrobial photodynamic therapy (aPDT) on the count of Enterococcus faecalis (E. faecalis) using different light sources. The antimicrobial effect of aPDT with chlorophyllin–phycocyanin mixture using different light sources including diode laser (λ = 660 nm), diode laser (λ = 635 nm), LED (λ = 450 ± 30 nm) alone or in combination was assessed using microbial cell viability assay against E. faecalis. In addition, the cell cytotoxicity of Photoactive+ was assessed on human gingival fibroblast (HuGu) cells by MTT assay; E. faecalis growth when treated by both red wavelengths (635 nm, 660 nm) and combination of LED (420–480 nm) and red wavelengths (635 nm, 660 nm), significantly reduced compared to the control group (p < 0.05). There was no significant reduction in the number of viable cells exposed to Photoactive+ compared to the control group (p < 0.05). This study shows that the application of chlorophyllin–phycocyanin mixture and irradiation with emission of red light achieved a better result for bacterial count reduction, compared to a control. This component can be applied safely due to very negligible cytotoxicity.

Effective killing of bacteria under blue-light irradiation promoted by green synthesized silver nanoparticles loaded on reduced graphene oxide sheets

Graphene oxide (GO) materials loaded with silver nanoparticles (AgNPs) have drawn considerable attention due to their capacity to efficiently inactivate bacteria though a multifaceted mechanism of action, as well as for presenting a synergetic effect against bacteria when compared to the activity of AgNPs and GO alone. In this investigation, we present an inexpensive and environmentally-friendly method for synthesizing reduced GO sheets coated with silver nanoparticles (AgNPs/r-GO) using a coffee extract solution as a green reducing agent. The physical and chemical properties of the produced materials were extensively characterized by scanning electron microscopy (SEM), field-emission gun transmission electron microscopy (FEG-TEM), ultraviolet and visible absorption (UV-Vis), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ion release determination. The results demonstrated that AgNPs/r-GO composites were successfully produced, revealing the formation of micrometer-sized r-GO sheets decorated by AgNPs of approximately 70 nm diameter. Finally, bactericidal and photobactericidal effects of the AgNPs/r-GO composites were tested against Staphylococcus aureus, in which the results showed that the composites presented antimicrobial and photoantimicrobial activities. Moreover, our results demonstrated for the first time, to our knowledge, that an efficient process of bacterial inactivation can be achieved by using AgNPs/r-GO composites under blue light irradiation as a result of three different bacterial killing processes: (i) chemical effect promoted by Ag⁺ ion release from AgNPs; (ii) photocatalytic activity induced by AgNPs/r-GO composites, enhancing the bacterial photoinactivation due to the excited-Plasmons of the AgNPs when anchored on r-GO; and (iii) photodynamic effect produced by bacterial endogenous photosensitizers under blue-light irradiation. In summary, the present findings demonstrated that AgNPs/r-GO can be obtained by a non-toxic procedure with great potential for biomedical-related applications.

The ineffectiveness of antimicrobial photodynamic therapy in the absence of preincubation of the microorganisms in the photosensitizer

Abstract Introduction: Considering its potential as an alternative therapy to combat multiresistant bacteria, photodynamic therapy has been improved and better studied in recent years, and determining its optimized application patterns is important. Objective: This study aimed to evaluate the action of antimicrobial photodynamic therapy mediated by methylene blue in the absence of preincubation of infectious agents in the photosensitizer. Method: Standard strains of Staphylococcus aureus and Pseudomonas aeruginosa were used, which was or was not submitted to two methylene blue concentrations (0.1 μg/mL and 500 mg/mL) applied alone or in combination with a variety of red laser emission parameters (660 nm); in both cases, the streak was performed immediately after mixing between the photosensitizer and the solution containing the bacteria. Results: In the dishes with only methylene blue application neither antibacterial was produced, nor inhibition at the application points of the photodynamic therapy in the case of the bacterium Pseudomonas aeruginosa. However, in the cultures of Staphylococcus aureus in which laser emission was associated with the concentration of 500 mg/mL of the photosensitizer, inhibition was present at the laser application points. Conclusion: The time of exposure to the photosensitizer prior to the application of phototherapy seems to be an essential factor for the optimized action of photodynamic therapy, especially in the case of Gram-negative bacteria.

Evaluating the applicability of multi-energy calibration as an alternative method for quantitative molecular spectroscopy analysis

Multi-Energy Calibration (MEC) was recently proposed as an innovative analytical method to be used in efficient and accurate quantitative analysis based on atomic spectroscopy. Here, the applicability of the MEC method for quantifying molecular species using UV-Vis and fluorescence measurements was evaluated for the first time. UV-Vis and fluorescence spectra of the analytical solutions of methylene blue and eosin-methylene blue in two different solvents (distilled-deionized water and methanol) were collected. MEC showed high precision and sensitivity for determining the analyte concentration, providing similar limit of detection and quantification when compared with conventional analytical methods, such as external standard calibration and standard additions. Therefore, the present study has shown that MEC can be successfully applied for quantifying molecular species in a simple and efficient way accounting UV-Vis and fluorescence spectroscopy.

Evaluation of physicochemical properties and bacterial photoinactivation of phenothiazine photosensitizers

We report herein the physicochemical properties and antimicrobial activity of a new monobrominated derivative of Azure B and its parent compound.

Photoactivated Self-Sanitizing Chlorophyllin-Containing Coatings to Prevent Microbial Contamination in Packaged Food

Chlorophyllins are semi-synthetic porphyrins obtained from chlorophyll that—when exposed to visible light—generate radical oxygen substances with antimicrobial activity. In this work, chlorophyllins incorporated with polyethylene (PE), polyvinyl alcohol (PVOH), (hydroxypropyl)methyl cellulose (HPMC), and gelatin (G) were formulated for application as coatings in packages providing antimicrobial activity after photoactivation. First, the antimicrobial properties of two porphyrins (sodium magnesium chlorophyllin, E-140, and sodium copper chlorophyllin, E-141) were analyzed against L. monocytogenes and Escherichia coli. The results indicated that E-140 was more active than E-141 and that chlorophyllins were more effective against Gram-positive bacteria. In addition, both chlorophyllins were more efficient when irradiated with halogen lamps than with LEDs, and they were inactive in dark conditions. Then, coatings on polyethylene terephthalate (PET) film were prepared, and their effect against the test bacteria was similar to that shown previously with pure chlorophyllins, i.e., greater activity in films containing E-140. Among the coating matrices, those based on PE presented the least effect (1 log reduction), whereas PVOH, HPMC, and G were lethal (7 log reduction). The self-sanitizing effect of these coatings was also analyzed by contaminating the surface of the coatings and irradiating them through the PET surface, which showed high efficiency, although the activity of the coatings was limited to L. monocytogenes. Finally, coated films were applied as separators of bologna slices. After irradiation, all the films showed count reductions of L. monocytogenes and the usual microbial load; the gelatin coating was the most effective, with an average of 3 log reduction.

Evaluation of Eosin-Methylene Blue as a Photosensitizer for Larval Control of Aedes aegypti by a Photodynamic Process

Aedes aegypti (Ae. aegypti) is a competent vector for transmitting important viral diseases such as yellow fever, dengue, chikungunya, and Zika. Several strategies have been applied to avoid Ae. aegypti proliferation by using environmental management, biological, and chemical approaches. However, the development of new methods for effective control of the insect vector population is still needed. Photodynamic control is an alternative way to control the vector population by using a physical approach based on the larval phototoxicity of a photosensitizer. In this context, the present study evaluated the use of eosin-methylene blue (EMB) as a new photosensitizer for photodynamic control of Ae. aegypti larval populations. The photodynamic assays were performed submitting Ae. aegypti third-instar larvae to different EMB concentrations (0.0, 0.5, 1.0, 5.0, 10.0, 50.0, and 100.0 µg mL⁻¹) in combination of three different light doses (24.3, 48.6, and 97.2 J cm⁻²) under either white-light radiation from RGB LEDs or sunlight. The results demonstrated that EMB presented a rapid internalization into the larvae and was phototoxic. The photodynamic action induced 100% of larval mortality after about 40 min of sunlight irradiation even using low EMB concentration (0.5 µg mL⁻¹). The findings reveal EMB as an effective photoactive compound to control larval populations of Ae. aegypti by photodynamic process induced by either sunlight or white-light from RGB LEDs.

Effect of photodynamic inactivation of Escherichia coli by hypericin

The present study has focused on the effects of hypericin (Hyp) based photodynamic inactivation (PDI) of Escherichia coli (E. coli). To evaluate the efficiency of Hyp based PDI of E. coli, single factor experiments and response surface optimization experiment were conducted to obtain the optimum parameter values (36 µM Hyp, 5.9 J cm^-2 light dose: 16.4 mW cm^-2, 60 W, 260 s, 590 nm and 68 min incubation time) and finally achieved a 4.1 log CFU mL^-1 decrease of E. coli. Cell-Hyp interaction and intracellular reactive oxygen species (ROS) level were detected by fluorescence spectrometric photometer. Data indicated that Hyp possessed a strong ability to bind with cells. In addition, a significant increase was observed in intracellular ROS level after Hyp-based photosensitization treatment. Therefore, Hyp-based photosensitization seems to be a promising method to efficiently inactivate E. coli. It is expected to be a safe, efficient, low cost and practical method which can be applied in the field of food safety.

Antimicrobial properties of a new type of photosensitizer derived from phthalocyanine against planktonic and biofilm forms of Staphylococcus aureus

BACKGROUND

Bacterial infection is a common clinical problem. Community-associated Staphylococcus aureus (S. aureus) infections can cause extensive tissue damage and necrosis. Photodynamic antimicrobial chemotherapy (PACT) has recently attracted attention as a feasible bacterial therapy. Octa-cationic zinc phthalocyanines are newly identified photosensitizers derived from phthalocyanines bearing 1, 2-ethanediamine groups and quaternized derivatives with different numbers of positive charges (ZnPcⁿ⁺, n = 4 or 8). Here we report the antimicrobial effects of ZnPcⁿ⁺-mediated PACT on planktonic and biofilm cultures of S. aureus.

METHODS

ZnPcⁿ⁺ uptake was detected by photometry after alkaline lysis. Dark-toxicity and light-mediated antimicrobial effects of the drug was determined by the plate count method. The production of intracellular reactive oxygen species (ROS) was detected by flow cytometry. SYTO 9 and propidium iodide (PI) were used to detect the bacterial cell membrane permeability. DNA damage after ZnPcⁿ⁺-PACT was analyzed by flow cytometry and PI staining. The destruction of biofilm was evaluated by scanning electron microscope (SEM).

RESULTS

The study of uptake showed that the relative fluorescence intensity of ZnPcⁿ⁺ in S. aureus peaked at 15 min. Generation of reactive oxygen species (ROS) by ZnPcⁿ⁺ was enhanced in PACT treatment groups. SYTO 9 and PI staining indicated that cell membrane was damaged. Flow cytometry and PI staining revealed DNA damage. Biofilms were damaged in PACT treatment groups.

CONCLUSIONS

Our results suggest that light-activated ZnPcⁿ⁺ can efficiently inhibit planktonic and biofilm cultures of S. aureus.