Preservation effects of photodynamic inactivation-mediated antibacterial film on storage quality of salmon fillets: Insights into protein quality

The preservation effects of a photodynamic inactivation (PDI)-mediated polylactic acid/5-aminolevulinic acid (PLA/ALA) film on the storage quality of salmon fillets were investigated. Results showed that the PDI-mediated PLA/ALA film could continuously generate reactive oxygen species by consuming oxygen to inactivate native pathogens and spoilage bacteria on salmon fillets. Meanwhile, the film maintained the content of muscle proteins and their secondary and tertiary structures, as well as the integrity of myosin by keeping the activity of Ca2+-ATPase, all of which protected the muscle proteins from degradation. Furthermore, the film retained the activity of total superoxide dismutase (T-SOD), suppressed the accumulation of lipid peroxides (e.g., MDA), which greatly inhibited four main types of protein oxidations. As a result, the content of flavor amino acids and essential amino acids in salmon fillets was preserved. Therefore, the PDI-mediated antimicrobial packaging film greatly preserves the storage quality of aquatic products by preserving the protein quality.

Fabrication and characterization of microporous soft templated photoactive 3D materials for water disinfection in batch and continuous flow

Water cleaning can be provided in batch mode or in continuous flow. For the latter, some kind of framework must withhold the cleaning agents from washout. Porous structures provide an ideal ratio of surface to volume for optimal access of the water to active sites and are able to facilitate rapid and efficient fluid transport to maintain a constant flow. When functionalized with suitable photoactive agents, they could be used in solar photocatalytic disinfection. In this study, we have used the sugar cube method to fabricate PDMS-based materials that contain three different classes of photosensitizers that differ in absorption wavelength and intensity, charge as well as in ability to generate singlet oxygen. The obtained sponges are characterized by scanning electron microscopy and digital microscopy. Archimede's method was used to measure porosity and density. We show that the materials can absorb visible light and generate Reactive Oxygen Species (ROS) that are required to kill bacteria. The disinfection ability was tested by examining how irradiation time and operation mode (batch vs. flow) contribute to the performance of the material. The current strategy is highly adaptable to other (medium) pressure-driven flow systems and holds promising potential for various applications, including continuous flow photoreactions.

Ascorbic acid potentiates photodynamic inactivation mediated by octyl gallate and blue light for rapid eradication of planktonic bacteria and biofilms

This study reported for the first time that Ascorbic acid (AA) could appreciably boost the efficiency of Octyl gallate (OG)-mediated photodynamic inactivation (PDI) on Escherichia coli and Staphylococcus aureus in planktonic and biofilm states. The combination of OG (0.075 mM) and AA (200 mM) with 420 nm blue light (212 mW/cm2) led to a >6 Log killing within only 5 min for E. coli and S. aureus and rapid eradication of biofilms. The mechanism of action appears to be the generation of highly toxic hydroxyl radicals (•OH) via photochemical pathways. OG was exposed to BL irradiation to generate various reactive oxygen radicals (ROS) and the addition of AA could transform singlet oxygen (1O2) into hydrogen peroxide (H2O2), which could further react with AA to generate enormous •OH. These ROS jeopardized bacteria and biofilms by nonspecifically attacking various biomacromolecules. Overall, this PDI strategy provides a powerful microbiological decontamination modality to guarantee safe food products.

A protocol for an overview of systematic reviews to map photodynamic inactivation evidence in different dental specialties

This is a protocol for an overview to summarize the findings of Systematic Reviews (SR) dealing with Photodynamic Inactivation (PDI) for control of oral diseases. Specific variables of oral infectious will be considered as outcomes, according to dental specialty. Cochrane Database of Systematic Reviews (CDSR), MEDLINE, LILACS, Embase, and Epistemonikos will be searched, as well as reference lists. A search strategy was developed for each database using only terms related to the intervention (PDI) aiming to maximize sensitivity. After checking for duplicate entries, selection of reviews will be performed in a two-stage technique: two authors will independently screening titles and abstracts, and then full texts will be assessed for inclusion/exclusion criteria. Any disagreement will be resolved through discussion and/or consultation with a third reviewer. Data will be extracted following the recommendations in Chapter V of Cochrane Handbook and using an electronic pre-specified form. The evaluation of the methodological quality and risk of bias (RoB) of the SR included will be carried out using the AMSTAR 2 and ROBIS. Narrative summaries of relevant results from the individual SR will be carried out and displayed in tables and figures. A specific summary will focus on PDI parameters and study designs, such as the type and concentration of photosensitizer, pre-irradiation time, irradiation dosimetry, and infection or microbiological models, to identify the PDI protocols with clinical potential. We will summarize the quantitative results of the SRs narratively.

Photodynamic Inactivation of Staphylococcus aureus Using Aloe-emodin as Photosensitizer

Aloe-emodin (AE) is a natural compound with photodynamic properties. The aim of this study was to investigate the inhibitory effect of AE-mediated photodynamic inactivation (PDI) on Staphylococcus aureus (S. aureus). The bacteriostatic efficiency under different photodynamic conditions and photosensitizing mechanism was studied in detail. The results showed that AE-mediated PDI exhibited a typical concentration and time-dependent characteristics. In terms of bactericidal mechanism, disruption of membrane integrity and increase of cell membrane permeability was observed. Type II reaction was assumed as the main photochemical reaction involved in AE-mediated PDI as evidenced by the action of different ROS quenching agents. Furthermore, AE-mediated PDI decreased the bacterial survival in freshly squeezed apple juice and maintained its quality. The combination of blue light and AE enlarged the application of AE as an effective natural photosensitizer suitable for a food system.

Porphyrin-based covalent organic polymers with customizable photoresponses for photodynamic inactivation of bacteria

Porphyrin-linked covalent organic polymers (COPs) provide a reliable photocatalytic platform, while photodynamic inactivation (PDI) induced by reliable porphyrin-based COPs is considered to be an effective method to resist microbial contamination. Herein, three tunable porphyrin-based covalent organic polymers (H2-Por-COPs, OH-Por-COPs, and Zn-Por-COPs) are designed and employed for the PDI of Staphylococcus aureus and Escherichia coli under visible light illumination. Interestingly, singlet oxygen (1O2) generation by the Por-COPs can be manipulated via intramolecular regulation with the order Zn-Por-COP > OH-Por-COP > H2-Por-COP. With rationally tune, the Zn-Por-COP demonstrated remarkable antibacterial activity against Staphylococcus aureus (kill percentage 99.65 % ± 0.24 %) and Escherichia coli (kill percentage 97.25 % ± 1.78 %) in only 15 min under visible-light irradiation. Density functional theory (DFT) calculations and photophysical tests showed that the presence of electron-donating -OH groups on the aromatic linkers and Zn2+ ions in porphyrin units narrowed the HOMO-LUMO gap, enhancing both light absorption, intersystem crossing (ISC) and 1O2 generation for more efficient bacteria inactivation. This work can be applied to efficiently screen suitable photosensitizers and provides a rational regulatory strategy for PDI of pathogenic bacteria.

Photoantimicrobial chitosan-gelatin-pomegranate peel extract films for strawberries preservation: From microbiological analysis to in vivo safety assessment

This study aimed to investigate the application of biopolymeric materials (chitosan, gelatin, and pomegranate peel extract as photosensitizer) and antimicrobial photodynamic therapy (aPDT) on the physicochemical and microbial safety of strawberries. The photosensitizer potential of the materials was confirmed by a light-dose-dependent photobleaching profile. The application of light (525 nm; 50 J cm-2) decreased by >2 log CFU mL-1 the survival of Staphylococcus aureus on the surface of the photoactive-biopolymeric films. Moreover, the materials did not present in vivo cytotoxicity using Danio rerio (Zebrafish) as well as cytophytotoxic, genotoxic, or mutagenic potentials against Allium cepa plant model, which points out their safety to be used as films without posing a risk to the humans and the environment. The photoactive-polymeric coatings were able to maintain the strawberries weight, and the association with green light was 100 % effective in delaying fungal contamination. These coated-strawberries presented a significant reduction in S. aureus survival after light application (5.47-4.34 log CFU mL-1). The molecular level analysis of the photoactive compound cyanidin-3-glucoside indicates absorption on UV-Vis consistent with aPDT action. Therefore, this study showed that the antimicrobial effects of aPDT combined with photoactive-biopolymeric coatings were enhanced, while the quality of the strawberries was maintained.

Photodynamic inactivation of bacteria: Why it is not enough to excite a photosensitizer

BACKGROUND

The development of multidrug resistance (MDR) in infectious agents is one of the most serious global problems facing humanity. Antimicrobial photodynamic therapy (APDT) shows encouraging results in the fight against MDR pathogens, including those in biofilms.

METHODS

Photosensitizers (PS), monocationic methylene blue, polycationic and polyanionic derivatives of phthalocyanines, electroneutral and polycationic derivatives of bacteriochlorin were used to study photodynamic inactivation of Gram-positive and Gram-negative planktonic bacteria and biofilms under LED irradiation. Zeta potential measurements, confocal fluorescence imaging, and coarse-grained modeling were used to evaluate the interactions of PS with bacteria. PS aggregation and photobleaching were studied using absorption and fluorescence spectroscopy.

RESULTS

The main approaches to ensure high efficiency of bacteria photosensitization are analyzed.

CONCLUSIONS

PS must maintain a delicate balance between binding to exocellular and external structures of bacterial cells and penetration through the cell wall so as not to get stuck on the way to photooxidation-sensitive structures of the bacterial cell.

Physico-mechanical and antimicrobial properties of an elastomeric ligature coated with reduced nanographene oxide-nano curcumin subjected to dual-modal photodynamic and photothermal inactivation against Streptococcus mutans biofilms

BACKGROUND

White spot lesions (WSLs) are a common side effect of fixed orthodontic treatment. Streptococcus mutans is the primary causative agent of WSLs and dental caries on the teeth during treatment. According to the unique features of reduced graphene oxide-nano curcumin (rGO-nCur), this study aimed to investigate the mechanical properties and antimicrobial potency of rGO-nCur coated orthodontic elastomeric ligatures as a novel coating composite following dual-modal photodynamic inactivation (PDI) and photothermal inactivation (PTI) against S. mutans biofilms.

METHODS

After confirmation of rGO-nCur synthesis and coating elastomeric ligatures with different concentration levels of 1.25, 2.5, 5, 7.5, and 10 % of rGO-nCur, tensile strength, force decay, extension to tensile strength, and contact angle of the coated elastomeric ligatures were measured using universal testing machine and sessile drop method, respectively. To investigate the mechanism through which irradiated rGO-nCur can inhibit the formation of S. mutans biofilms, intracellular reactive oxygen species (ROS) generation, and increase in temperature of rGO-nCur solutions under the 450 and 980 nm laser irradiation, respectively, were measured. The anti-biofilm activity and inhibition of water-insoluble extracellular polysaccharide (EPS) production ability of irradiated rGO-nCur coated elastomeric ligatures using a 450 nm diode laser (195 J/cm2), a 980 nm diode laser (195 J/cm2), and a combination of both (78 J/cm2 of irradiation from each one) (i.e., PDI, PTI, and dual-modal PDI/PTI, respectively) were determined. Also, the expression of virulence genes involved in biofilm formation (comDE, gtfD, and smuT) was assessed by quantitative real-time polymerase chain reaction (RT-qPCR) following the mentioned treatment. One-way ANOVA test and Tukey post-hoc test at a p-value equal to/or less than 0.05 were used to analyze the obtained data.

RESULTS

The synthesis of GO nano-sheets in a layered structure with a thickness of 0.76 nm was confirmed by AFM analysis. FESEM showed that the exfoliated sheet of synthesized GO had several micrometers in lateral size. DLS revealed that the mean particle size and density index of synthesized nCur were 57.47 ± 2.14 nm and 10 % respectively. In DLS analysis, rGO-nCur showed more positive surface charge (24 mV) than the nano-sheets of GO. FESEM confirmed the coating of rGO-nCur on elastomeric ligatures. ANOVA revealed that tensile strength of 1.25, 2.5, and 5 % rGO-nCur coated elastomeric ligatures were not decreased statistically significantly (P > 0.05). Mean tensile strength and recorded force of 7.5 and 10 % rGO-nCur coated elastomeric ligatures decreased significantly after 14 days' immersion in the artificial saliva (P < 0.05). On the 28th day of the study, the mean of the tensile strength of elastomeric ligatures coated with 10 % rGO-nCur (13.03 ± 0.10 N) was recorded as 55.90 % of the initial tensile strength (23.31 ± 0.41 N in uncoated elastomeric ligatures), while the mean tensile strength of elastomeric ligatures coated with 7.5 % rGO-nCur (16.01 ± 0.10 N) was measured as 68.94 % of the initial tensile strength (23.22 ± 0.09 N in uncoated elastomeric ligatures). When comparing the coated elastomeric ligatures at 7.5 % and 10 % to the original uncoated elastomeric ligatures at similar time intervals, statistically significant decreases in extension to tensile strength (0.42 to 0.71 mm or 3.02 to 5.05 %; all P < 0.05) were observed. The largest contact angle was measured in elastomeric ligatures coated by 10 % rGO-nCur followed by 7.5 and 5 % rGO-nCur (128 ± 2.19°, 117 ± 2.23°, and 99 ± 1.83°; respectively). The results revealed a rise of 6.4-fold in intracellular ROS and an 11.2 °C increase in the temperature of rGO-nCur solutions following the 450 nm and 980 nm laser irradiation, respectively. The 5 % rGO-nCur coated elastomeric ligature mediated dual-modal PDI/PTI showed the most inhibition of the biofilm formation of S. mutans by 83.62 % (P = 0.00). Significant reductions in water-insoluble EPS were detected in biofilm cultures of S. mutans on 1.25 % rGO-nCur coated elastomeric ligatures following irradiation with dual waves of the 450 nm and 980 nm diode lasers (i.e., dual-modal PDI/PTI; 96.17 %; P = 0.00). The expression levels of comDE, gtfD, and smuT virulence genes were significantly downregulated (7.52-, 13.92-, and 8.23-fold, respectively) in the biofilm cultures of S. mutans on 1.25 % rGO-nCur coated elastomeric ligatures following dual-modal PDI/PTI in comparison with biofilm cultures on non-coated elastomeric ligatures.

CONCLUSION

5 % rGO-nCur coated elastomeric ligatures following irradiation with dual waves of the 450 and 980 nm diode lasers (dual-modal PDI/PTI), without adverse effects on the physico-mechanical properties of elastomeric ligatures, can be used to inhibit the formation of S. mutans biofilms on the coated elastomeric ligatures around orthodontic brackets.

Impact of mucus and biofilm on antimicrobial photodynamic therapy: Evaluation using Ruthenium(II) complexes

The biofilm lifestyle of bacterial pathogens is a hallmark of chronic lung infections such as in cystic fibrosis (CF) patients. Bacterial adaptation to the complex conditions in CF-affected lungs and repeated antibiotherapies lead to increasingly tolerant and hard-to-treat biofilms. In the context of growing antimicrobial resistance and restricted therapeutic options, antimicrobial photodynamic therapy (aPDT) shows great promise as an alternative to conventional antimicrobial modalities. Typically, aPDT consists in irradiating a non-toxic photosensitizer (PS) to generate reactive oxygen species (ROS), which kill pathogens in the surrounding environment. In a previous study, we reported that some ruthenium (II) complexes ([Ru(II)]) can mediate potent photodynamic inactivation (PDI) against planktonic cultures of Pseudomonas aeruginosa and Staphylococcus aureus clinical isolates. In the present work, [Ru(II)] were further assayed to evaluate their ability to photo-inactivate such bacteria under more complex experimental conditions better recapitulating the microenvironment in lung infected airways. Bacterial PDI was tentatively correlated with the properties of [Ru(II)] in biofilms, in mucus, and following diffusion across the latter. Altogether, the results obtained demonstrate the negative impacting role of mucus and biofilm components on [Ru(II)]-mediated PDT, following different possible mechanisms of action. Technical limitations were also identified that may be overcome, making this report a pilot for other similar studies. In conclusion, [Ru(II)] may be subjected to specific chemical engineering and/or drug formulation to adapt their properties to the harsh micro-environmental conditions of the infected respiratory tract.

Photodynamic inactivation by hypericin-P123 on azole-resistant isolates of the Trichophyton rubrum complex as planktonic cells and biofilm

INTRODUCTION

The Trichophyton rubrum complex comprises the majority of dermatophyte fungi (DM) responsible for chronic cases of onychomycosis, which is treated with oral or topical antifungals. However, owing to antifungal resistance, alternative therapies, such as photodynamic therapy (PDT), are needed. This study investigated the frequency of the T. rubrum species complex in onychomycosis cases in the northwestern region of Paraná state, Brazil, and evaluated the efficacy of (PDT) using P123-encapsulated hypericin (Hyp-P123) on clinical isolates of T. rubrum in the planktonic cell and biofilm forms.

MATERIAL AND METHODS

The frequency of the T. rubrum complex in onychomycosis cases from 2017 to 2021 was evaluated through a data survey of records from the Laboratory of Medical Mycology (LEPAC) of the State University of Maringa (UEM). To determine the effect of PDT-Hyp-P123 on planktonic cells of T. rubrum isolates, 1 × 105 conidia/mL were treated with ten different concentrations of Hyp-P123 and then irradiated with 37.8 J/cm2. Antibiofilm activity of PDT-Hyp-P123 was tested against T. rubrum biofilm in the adhesion phase (3 h), evaluated 72 h after irradiation (37.8 J/cm2), and the mature biofilm (72 h), evaluated immediately after irradiation. In this context, three different parameters were evaluated: cell viability, metabolic activity and total biomass.

RESULTS

The T. rubrum species complex was the most frequently isolated DM in onychomycosis cases (approximately 80 %). A significant reduction in fungal growth was observed for 75 % of the clinical isolates tested with a concentration from 0.19 μmol/L Hyp-P123, and 56.25 % had complete inhibition of fungal growth (fungicidal action); while all isolates were azole-resistant. The biofilm of T. rubrum isolates (TR0022 and TR0870) was inactivated in both the adhesion phase and the mature biofilm.

CONCLUSION

PDT-Hyp-P123 had antifungal and antibiofilm activity on T. rubrum, which is an important dermatophyte responsible for onychomycosis cases.

Selective, broad-spectrum antiviral photodynamic disinfection with dicationic imidazolyl chlorin photosensitizers

The COVID-19 pandemic exposes our vulnerability to viruses that acquire the ability to infect our cells. Classical disinfection methods are limited by toxicity. Existing medicines performed poorly against SARS-CoV-2 because of their specificity to targets in different organisms. We address the challenge of mitigating known and prospective viral infections with a new photosensitizer for antimicrobial photodynamic therapy (aPDT). Photodynamic inactivation is based on local oxidative stress, which is particularly damaging to enveloped viruses. We synthesized a cationic imidazolyl chlorin that reduced by > 99.999% of the percentage inhibition of amplification of SARS-CoV-2 collected from patients at 0.2 µM concentration and 4 J cm-2. Similar results were obtained in the prevention of infection of human ACE2-expressing HEK293T cells by a pseudotyped lentiviral vector exhibiting the S protein of SARS-CoV-2 at its surface. No toxicity to human epidermal keratinocytes (HaCaT) cells was found under similar conditions. aPDT with this chlorin offers fast and safe broad-spectrum photodisinfection and can be repeated with low risk of resistance.

Curcumin and carvacrol mediated photodynamic inactivation with 405 nm light emitting diodes (LEDs) on Salmonella Enteritidis

Photodynamic inactivation (PDI) has a potential application for food preservation that can minimize food pathogens posing risks to consumer health. This study aimed to evaluate the antibacterial activity of 405 nm light-emitting diodes (LEDs) illumination in the presence of carvacrol and curcumin against Salmonella Enteritidis and S. Enteritidis PT4 at different temperatures (4 °C, 25 °C and 37 °C) and time parameters (15 min, 30 min and 45 min) in the illumination system. Compared to their individual treatment, the decrease in the bacterial population was stronger in bacteria treated with LEDs + carvacrol or LEDs + curcumin. Co-application of carvacrol or curcumin with LEDs at 37 °C showed strong antibacterial activity against both bacteria depending on the application time. Co-application at 37 °C for 45 min completely inhibited the growth of S. Enteritidis. LEDs, curcumin, carvacrol applications alone or LEDs + curcumin, LEDs + carvacrol applications caused a decrease in bacterial population in proportion to the increase in the storage temperature and application times. These results showed that carvacrol or curcumin potentiates LEDs illumination therapy against both bacteria. Future studies on adapting the PDI system to control bacteria in a variety of foods may help develop novel strategies to fight against foodborne bacterial pathogens.

Antiviral activity of singlet oxygen-photogenerating perylene compounds against SARS-CoV-2: Interaction with the viral envelope and photodynamic virion inactivation

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has prompted great interest in novel broad-spectrum antivirals, including perylene-related compounds. In the present study, we performed a structure-activity relationship analysis of a series of perylene derivatives, which comprised a large planar perylene residue, and structurally divergent polar groups connected to the perylene core by a rigid ethynyl or thiophene linker. Most of the tested compounds did not exhibit significant cytotoxicity towards multiple cell types susceptible to SARS-CoV-2 infection, and did not change the expressions of cellular stress-related genes under normal light conditions. These compounds showed nanomolar or sub-micromolar dose-dependent anti-SARS-CoV-2 activity, and also suppressed the in vitro replication of feline coronavirus (FCoV), also termed feline infectious peritonitis virus (FIPV). Perylene compounds exhibited high affinity for liposomal and cellular membranes, and efficiently intercalated into the envelopes of SARS-CoV-2 virions, thereby blocking the viral-cell fusion machinery. Furthermore, the studied compounds were demonstrated to be potent photosensitizers, generating reactive oxygen species (ROS), and their anti-SARS-CoV-2 activities were considerably enhanced after irradiation with blue light. Our results indicated that photosensitization is the major mechanism underlying the anti-SARS-CoV-2 activity of perylene derivatives, with these compounds completely losing their antiviral potency under red light. Overall, perylene-based compounds are broad-spectrum antivirals against multiple enveloped viruses, with antiviral action based on light-induced photochemical damage (ROS-mediated, likely singlet oxygen-mediated), causing impairment of viral membrane rheology.

Strengthening collaborations at the Biology-Physics interface: trends in antimicrobial photodynamic therapy

The unbridled use of antimicrobial drugs over the last decades contributed to the global dissemination of drug-resistant pathogens and increasing rates of life-threatening infections for which limited therapeutic options are available. Currently, the search for safe, fast, and effective therapeutic strategies to combat infectious diseases is a worldwide demand. Antimicrobial photodynamic therapy (APDT) rises as a promising therapeutic approach against a wide range of pathogenic microorganisms. APDT combines light, a photosensitizing drug (PS), and oxygen to kill microorganisms by oxidative stress. Since the APDT field involves branches of biology and physics, the strengthening of interdisciplinary collaborations under the aegis of biophysics is welcome. Given this scenario, Brazil is one of the global leaders in the production of APDT science. In this review, we provide detailed reports of APDT studies published by the Laboratory of Optical Therapy (IPEN-CNEN), Group of Biomedical Nanotechnology (UFPE), and collaborators over the last 10 years. We present an integrated perspective of APDT from basic research to clinical practice and highlight its promising use, encouraging its adoption as an effective and safe technology to tackle important pathogens. We cover the use of methylene blue (MB) or Zn(II) porphyrins as PSs to kill bacteria, fungi, parasites, and pathogenic algae in laboratory assays. We describe the impact of MB-APDT in Dentistry and Veterinary Medicine to treat different infectious diseases. We also point out future directions combining APDT and nanotechnology. We hope this review motivates further APDT studies providing intuitive, vivid, and insightful information for the readers.

Photodynamic activity enhanced by in situ biosynthetic BC/CQDs@PCN-224 membranes through FRET strategy

Porphyrin-based metal organic frameworks (MOFs) with efficient bactericidal performance have increasingly attracted attention in photodynamic inactivation materials. However, low reactive oxygen species (ROS) yield and drug residue hazards of current porphyrin-MOFs materials lead to unsatisfactory clinical therapeutic effects. In this paper, carbon quantum dots (CQDs) were encapsulated into PCN-224, which enhanced the photodynamic activity of the MOFs through fluorescence resonance energy transfer (FRET) process. Singlet oxygen (¹O₂) detection confirmed that the photodynamic activity of CQDs-doped PCN-224 (CQDs@PCN-224) was enhanced than that of pristine PCN-224 under illumination. Furthermore, the CQDs@PCN-224 were firmly embedded into bacterial cellulose (BC) nanofibrous membranes by using an eco-friendly biosynthetic approach, efficiently preventing MOFs leakage during use. The results of bactericidal assays demonstrated that BC/CQDs@PCN-224 membrane with higher photodynamic activity causes more severe disruption to bacterial structure and possesses better antibacterial efficiency (>99.99 % reduction of both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli O157:H7 within 30 min) than BC/PCN-224 membrane under visible light illumination (500 W, 15 cm height, λ ≥ 420 nm). In addition, the biosynthesized BC/CQDs@PCN-224 membrane showed good hemocompatibility and low cytotoxicity, revealing that the BC- and MOFs-based material with enhanced PDI efficiency and satisfying safety has great potential in medical fields.

Hydrogen peroxide enhanced photoinactivation of Candida albicans by a novel boron-dipyrromethene (BODIPY) derivative

Photodynamic inactivation (PDI) has received increasing attention as a promising approach to combat Candida albicans infections. This study aimed to evaluate the synergistic effect of a new BODIPY (4,4-difluoro-boradiazaindacene) derivative and hydrogen peroxide on C. albicans. BDP-4L in combination with H₂O₂ demonstrated enhanced photokilling efficacy. In suspended cultures of C. albicans, the maximum decrease was 6.20 log and 2.56 log for PDI using BDP-4L (2.5 μM) with or without H₂O₂, respectively. For mature C. albicans biofilms, 20 μM BDP-4L plus H₂O₂ eradicated C. albicans, causing an over 6.7 log count reduction in biofilm-associated cells, while only a reduction of ~ 1 log count was observed when H₂O₂ was omitted. Scanning electron microscopy analysis and LIVE/DEAD assays suggested that PDI using BDP-4L plus H₂O₂ induced more damage to the cell membrane. Correspondingly, amplification of nucleic acids release was observed in biofilms treated with the combined PDI. Additionally, we also discovered that the addition of hydrogen peroxide potentiated the generation of ¹O₂ in PDI using the singlet oxygen sensor green probe. Collectively, BDP-4L combined with H₂O₂ presents a promising approach in the treatment of C. albicans infections.

Color-variable dual-dyed photodynamic antimicrobial polyethylene terephthalate (PET)/cotton blended fabrics

The urgent demand for scalable, potent, color variable, and comfortable antimicrobial textiles as personal protection equipment (PPE) to help reduce infection transmission in hospitals and healthcare facilities has significantly increased since the start of the COVID-19 pandemic. Here, we explored photodynamic antimicrobial polyethylene terephthalate/cotton (TC) blended fabrics comprised of photosensitizer-conjugated cotton fibers and polyethylene terephthalate (PET) fibers dyed with disperse dyes. A small library of TC blended fabrics was constructed wherein the PET fibers were embedded with traditional disperse dyes dominating the fabric color, thereby enabling variable color expression, while the cotton fibers were covalently coupled with the photosensitizer thionine acetate as the microbicidal agent. Physical (SEM, CLSM, TGA, XPS and mechanical strength) and colorimetric (K/S and CIELab values) characterization methods were employed to investigate the resultant fabrics, and photooxidation studies with DPBF demonstrated the ability of these materials to generate reactive oxygen species (i.e., singlet oxygen) upon visible light illumination. The best results demonstrated a photodynamic inactivation of 99.985% (~ 3.82 log unit reduction, P = 0.0021) against Gram-positive S. aureus, and detection limit inactivation (99.99%, 4 log unit reduction, P ≤ 0.0001) against Gram-negative E. coli upon illumination with visible light (60 min; ~ 300 mW/cm²; λ ≥ 420 nm). Enveloped human coronavirus 229E showed a photodynamic susceptibility of ~ 99.99% inactivation after 60 min illumination (400-700 nm, 65 ± 5 mW/cm²). The presence of the disperse dyes on the fabrics showed no significant effects on the aPDI results, and furthermore, appeared to provide the photosensitizer with some measure of protection from photobleaching, thus improving the photostability of the dual-dyed fabrics. Taken together, these results suggest the feasibility of low cost, scalable and color variable thionine-conjugated TC blended fabrics as potent self-disinfecting textiles.

A new acridine-based photosensitizer with ultra-low light requirement efficiently inactivates carbapenem-resistant Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus and degrades their antibiotic resistance genes

The spread of antibiotic resistant pathogens and antibiotic resistance genes (ARGs) in the environment poses a serious threat to public health. However, existing methods are difficult to effectively remove antibiotic resistant pathogens and ARGs from the environment. In this study, we synthesized a new acridine-based photosensitizer, 2,7-dibromo-9-mesityl-10-methylacridinium perchlorate (YM-3), by the heavy atom effect, which could photodynamically inactivate antibiotic resistant pathogens and reduce ARGs by generating singlet oxygen (¹O₂) in an aqueous environment. The ¹O₂ yield of YM-3 was 4.9 times that of its modified precursor. YM-3 could reduce the culturable number and even the viable counts of methicillin-resistant Staphylococcus aureus and carbapenem-resistant Acinetobacter baumannii to 0 (inactivation rate > 99.99999%) after 2 and 8 h of low-intensity blue light (15 W/m²) irradiation, respectively. After 20 h of light exposure, the copy numbers of ARGs in both bacteria were reduced by 5.80 and 4.48 log, respectively, which might indicate that ARGs had been degraded. In addition, YM-3 still had an efficient bactericidal effect after five inactivation cycle. These characteristics of ultra-low light intensity requirement and efficient bactericidal ability make YM-3 have good application prospects for disinfection in indoor and sunlight environment.

The physiochemical and photodynamic inactivation properties of corn starch/erythrosine B composite film and its application on pork preservation

This study explored the effect of erythrosine B (EB) as a photosensitizer in corn starch (CS) film and its physicochemical properties and photodynamic bacteriostatic ability against Staphylococcus aureus, Escherichia coli, and Salmonella both in vitro and inoculated on pork under the irradiation of D65 light-emitting diode (LED) (400-800 nm). The study revealed that the physiochemical properties of CS films: moisture content, water solubility, and water vapor transmission were improved with the addition of EB. In addition, the elasticity and the thermal stability of the film were enhanced. The results showed that the CS-EB films stimulated a maximum of 26.36 μg/mL hydrogen peroxide and 74.5 μg/g hydroxyl radical under irradiation. The CS composite films with a 5 % concentration of EB inhibited the bacterial growth by 4.7 Log CFU/mL in vitro after 30 min of illumination, and 2.4 Log CFU/mL on the pork samples under the same experimental condition. Moreover, the antibacterial ability was enhanced with the increase in EB concentration. Overall, the CS-EB composite films can inhibit the growth of bacteria through photodynamic inactivation and has the potential to become a new type of environmentally friendly packaging material.

Antibacterial potential of riboflavin mediated blue diode laser photodynamic inactivation against Enterococcus faecalis: A laboratory investigation

OBJECTIVES

This study aimed to evaluate the inactivation potency of riboflavin-mediated blue diode laser photodynamic inactivation (PDI) against Enterococcus faecalis at planktonic and biofilm stages and also investigated its effect on the tooth color change.

MATERIALS AND METHODS

The antibacterial and antibiofilm activities of riboflavin mediated PDI against E. faecalis were investigated. The numbers of colony-forming units (CFUs)/mL were calculated. Teeth discoloration were evaluated using the CIE L*a*b* based color difference (ΔE).

RESULTS

Antibacterial analysis indicated that the blue diode laser irradiation at 12, 18, 24, and 30 J/cm² alone and different concentrations of riboflavin solution (6.25 to 100 μM) reduced the number of CFU/mL of E. faecalis, but the reduction was not statistically significant (P > 0.05). Depending on the riboflavin concentration and the light dose, there can be as much as a 1-log effect on CFU/mL. In addition, E. faecalis biofilm was more affected with 30 J/cm² irradiation dosage and 100 μM riboflavin than other groups. Meanwhile, bacterial suspensions treated with 5.25% sodium hypochlorite (NaOCl) showed maximum biofilm inhibition and colony number reduction, compared with the control. The teeth exhibited clinically acceptable color change after riboflavin treatment at concentration ranging from 6.25 to 50 μM (ΔE < 3.7).

CONCLUSIONS

The riboflavin mediated PDI process is somewhat less effective than NaOCl but perhaps less toxic to tissues. It might be feasible to repeat the riboflavin + light treatment to further promote efficacy.

Antimicrobial curcumin-mediated photodynamic inactivation of bacteria in natural bovine casing

BACKGROUND

Outbreaks related to food contamination by resistant microorganisms is a worldwide concern that, motivates industries and research institutions to search for affordable solutions. Among the solutions that have been proposed, Photodynamic Inactivation (PDI) of microorganisms has gained prominence, among other aspects, because it is easy to apply and does not generate microbial resistance.

METHODS

In this study, we used the association between curcumin solubilized with Tween and light in the photodynamic inactivation process, using light-emitting diodes with a wavelength of 430 nm for decontamination S. Typhimurium and K. pneumoniae from bovine casings used as wrappers for meat products. The result was verified by counting and comparing the number of colony-forming units of the treatment concerning the negative control.

RESULTS

The solubilizer, Tween 80, used does not change the optical absorption of curcumin. An optical fluence of 150J/cm² induces a microbial log reduction of 3.8±0.2 and 2.7±0.1 for S. Typhimurium, and K. pneumoniae contaminated guts, respectively. For the 200μM concentration of curcumin, the PDI provided a microbial log reduction of 3.16±0.03 for S. Typhimurium. For K. pneumoniae, the minimal inhibitory concentration of curcumin occurs up to 12.5μM, causing an microbial log reduction of 2.08±0.03.

CONCLUSION

Both curcumin and tween are already used as additives in food production and do not pose health risks at the concentrations used. Furthermore, in the case of the material studied, the addition of curcumin favors the organoleptic quality associated with the color of the food, unlike the green or blue photossensitizers. The results pave the way for possible application of curcumin in finished meat products.

Photodynamic inactivation of Staphylococcus aureus in the presence of aggregation-prone photosensitizers based on BODIPY used at submicromolar concentrations

Two new brominated BODIPYs (1 and 2) bearing amino acid-based chains (l-valine for 1, and dimethyl-l-lysine for 2) were synthesized and characterized. In organic solvents, 1 and 2 were fully soluble and showed the photophysical properties expected for brominated BODIPY dyes, including efficient generation of singlet oxygen (¹O₂), upon irradiation. In contrast, in aqueous media, both compounds were prone to aggregation and the photo-induced generation of ¹O₂ was halted. Despite the lack of generation of this reactive species in aqueous media (in cuvette), both 1 and 2 have positive antimicrobial Photodynamic Inactivation (aPDI) effect. The activity against gram-positive Staphylococcus aureus and gram-negative Escherichia coli was determined through the inactivation curves, with a total energy dose of 5.3 J/cm² (white light LED used as an energy source). Compound 2 was highly active against both gram-positive and gram-negative bacteria (3 log CFU/mL reduction was obtained at 0.16 μM for S. aureus and 2.5-5.0 μM for E. coli), whereas 1 was less effective to kill S. aureus (3 log CFU/mL at 0.32 μM) and ineffective for E. coli. The higher efficiency of 2, as compared to 1, to reduce the population of bacteria, can reside in the presence of a protonatable residue in 2, allowing a more effective interaction of this molecule with the cell walls of the microorganisms. In order to explain the lack of reactivity in pure aqueous media (in cuvette) and the contrasting good activity in the presence of bacterial cells it can be hypothesized that upon interaction with the walls of the microorganisms, the aggregated photosensitizers suffer a disaggregation process restoring the ability to generate ¹O₂, and hence leading to efficient photodynamic activity against these pathogenic microorganisms, in agreement with the similar effect observed recently for porphyrinoid photosensitizers.

Synergic dual phototherapy: Cationic imidazolyl photosensitizers and ciprofloxacin for eradication of in vitro and in vivo E. coli infections

The emergence of new microorganisms with resistance to current antimicrobials is one of the key issues of modern healthcare that must be urgently addressed with the development of new molecules and therapies. Photodynamic inactivation (PDI) in combination with antibiotics has been recently regarded as a promising wide-spectrum therapy for the treatment of localized topical infections. However, further studies are required regarding the selection of the best photosensitizer structures and protocol optimization, in order to maximize the efficiency of this synergic interaction. In this paper, we present results that demonstrate the influence of the structure of cationic imidazolyl-substituted photosensitizers and light on the enhancement of ciprofloxacin (CIP) activity, for the inactivation of Escherichia coli. Structure-activity studies have highlighted the tetra cationic imidazolyl porphyrin IP-H-Me⁴⁺ at sub-bactericide concentrations (4-16 nM) as the most promising photosensitizer for combination with sub-inhibitory CIP concentration (<0.25 mg/L). An optimized dual phototherapy protocol using this photosensitizer was translated to in vivo studies in mice wounds infected with E. coli. This synergic combination reduced the amount of photosensitizer and ciprofloxacin required for full E. coli inactivation and, in both in vitro and in vivo studies, the combination therapy was clearly superior to each monotherapy (PDI or ciprofloxacin alone). Overall, these findings highlight the potential of cationic imidazolyl porphyrins in boosting the activity of antibiotics and lowering the probability of resistance development, which is essential for a sustainable long-term treatment of infectious diseases.

Co-crystallization of curcumin for improved photodynamic inactivation of Vibrio parahaemolyticus and its application for the preservation of cooked clams

Curcumin (CUR) is a natural active product widely used as photosensitizer in photodynamic inactivation (PDI) due to low toxicity and low cost. However, the main challenge that limit the efficacy of CUR in PDI are its low solubility in water medium and hence low bioavailability. The co-crystallization is a novel process enables improvements in physicochemical properties such as solubility and bioavailability of water insoluble compound by the incidence of molecular interactions between the active pharmaceutical ingredient and conformer. The main objective of this work is to produce CUR-d-Tyr co-crystal (CDC) by co-crystallization technique using d-Tyrosine (d-Tyr) as the conformer in order to increase CUR water solubility as well as antimicrobial photodynamic activity. CDC presented a different crystalline structure compared with pure CUR. The solubility of CDC in water medium was about 16.5 times greater than pure CUR. The co-crystallization process increased CUR-mediated photodynamic inactivation efficacy of Vibrio parahaemolyticus (V. parahaemolyticus), probably due to alterations in its bioavailability. Moreover, cell membrane damage and production of cytotoxic singlet oxygen (¹O₂) was proved as main photosensitization mechanism. Furthermore, the application of CDC-mediated PDI on cooked clam reduced weightlessness of cooked clams, inhibited lipid oxidation, and maintained a better appearance, serving as a promising preservation techniques in food industry.

Photoinactivation of Salmonella enterica exposed to 5-aminolevulinic acid: Impact of sensitization conditions and irradiation time

The photodynamic inactivation (PDI) represents the potential alternative to traditional antibiotic therapy, and can be applied to treat various bacterial infections, including those caused by Gram-negative bacterial strains. One of the treatment modalities is based on the capacity of bacterial cells to synthesize the excess amounts of porphyrins after exposure to an externally applied 5-aminolevulinic acid (5-ALA), which makes them photosensitive and leads to reduced survival after irradiation with an appropriately selected light source. This study focuses on the sensitization and the photoinduced inactivation of Salmonella enterica cells in PBS containing 0.5 mM 5-ALA, incubated at 37 °C for 4 h or for 20 h and afterwards irradiated with violet LED light (11.1 mW/cm², a peak at 400 nm). It has been found that both amounts and composition of endogenous porphyrins not only depended on the incubation duration, but also were affected by externally induced photo- and chemo-oxidation reactions. The application of different sensitization conditions has revealed that the increasing amounts of endogenously produced porphyrins do not ensure the proportional reduction of bacterial cell survival numbers. The comparative investigations also demonstrated that the presence of endogenously produced porphyrins in the medium results in secondary sensitization of bacterial cells and causes a notably stronger photoinactivation effect in comparison to their externally applied standards.

Influence of photosensitizer concentration and polymer composition on photoinduced antimicrobial activity of PVA- and PVA-chitosan-based electrospun nanomaterials cross-linked with tailor-made silicon(IV) phthalocyanine

The ongoing effort to eradicate pathogenic bacteria and viruses is a major endeavor that requires development of new and innovative materials. Materials based on photodynamic action represent an emerging and attractive area of research, and therefore, a broad understanding of chemical design principles is required. In the present study, we investigated the antibacterial and antiviral activities of five different nanofibrous membranes composed of poly(vinyl alcohol) or poly(vinyl alcohol)-chitosan mixture cross-linked through silicon(IV)phthalocyanine derivative with the aim to identify the role of the carrier polymer and photosensitizers concentration on its efficacy. A straightforward cross-linking process was adopted to create a water-stable material with an almost uniform distribution of the fiber structure, as revealed by scanning electron microscopy. The results of the antimicrobial studies showed that the increase in the amount of chitosan in the polymer mixture, rather than the increase in the photosensitizer concentration, enhanced the activity of the material. Due to their visible light-triggered antimicrobial activity, the resulting materials provide valuable opportunities for both topical antimicrobial photodynamic therapy and the area of environmental remediation.

Impact of light-activated curcumin and curcuminoids films for catheters decontamination

BACKGROUND

Biofilms are microbial communities protected by an extra polymeric matrix, which promotes a defense against antimicrobial agents. Cells attached in surfaces and promote infections. Photodynamic inactivation (PDI) is one of the strategies to eliminate infections due to the facility of use and the absence of resistance by bacteria. The study combines formulation with curcuminoids and with Photogem^(R), illuminating them with 450 nm and 630 nm, respectively.

METHODS

Films were prepared with pectin, glycerin, Sodium Lauryl Sulfate, curcumin, curcuminoids, or Photogem^(R) (0.75; 0.75 mg/mL and 0.03 mg/mL respectively). Bacterial biofilms were formed during 3, 4, or 7 days on catheters and illumination with LED devices at 450 nm and 630 nm.

RESULTS

The best PDI applied in S. aureus 7-days biofilm with curcuminoid film. Photogem film was the best strategy for PDI in E. coli 7-day biofilm. Curcumin film promoted similar results with S. aureus and E. coli. Light penetration demonstrated a similar decreased exponential curve along the increase of thickness of biofilm.

CONCLUSION

Curcuminoids, curcumin and Photogem® show efficient solubilization and availability in formulation with relevant results in PDI. S aureus biofilms were more susceptible to curcuminoid film. E coli biofilms were more susceptible to Photogem film.

In vitro evaluation of the cis-[Ru(phen)2(pPDIp)]2+⁎⁎ complex for antimicrobial photodynamic therapy against Sporothrix brasiliensis and Candida albicans

BACKGROUND

Photodynamic therapy (PDT) activates a photosensitizer by visible light to generate cytotoxic oxygen species that lead to cell death. With proper illumination, PDT is often used in applications on superficial and sub-surface lesions. Sporotrichosis infection occurs by Sporothrix fungi which causes a skin wound, worsened by Candida albicans infections. This study investigated the photosensitizing efficiency of the Ru(phen)₂(pPDIp)(PF₆)₂ complex, RupPDIp, against S. brasiliensis and C. albicans.

MATERIAL AND METHODS

RupPDIp efficiency against these fungi was tested using 450 nm (blue light and 36 J/cm²) and 525 nm (green light, 25.2 J/cm²) at 0.05-20 μM concentrations. To ensure PDT effectiveness, control groups were tested in the absence and in the presence of RupPDIp under light irradiation and in the dark.

RESULTS

RupPDIp eliminated both fungi at ≤5.0 μM. Green light showed the best results, eliminating S. brasiliensis and C. albicans colonies at RupPDIp 0.5 μM and 0.05 μM, respectively.

CONCLUSION

RupPDIp is a promising photosensitizer in aPDT, eliminating 10⁶ CFU/mL of both fungi at 450 nm and 525 nm, with lower light doses and concentrations when treated with the green light compared to the blue light.

The zoonosis sporotrichosis can be successfully treated by photodynamic therapy: A scoping review

Sporotrichosis is a worldwide zoonosis, prevalent in tropical and subtropical regions. In recent years, there has been a substantial increase in human and feline cases reported in Brazil. Despite this, the antifungal treatment for sporotrichosis is still limited, and thus, research into new therapeutic modalities must be encouraged. Recently, photodynamic therapy has been introduced as a treatment for sporotrichosis. This work presents an overview of both in vitro and in vivo studies that have used photodynamic therapy in the context of photoinactivation of Sporothrix species. Until now, as far as the authors are aware, this is the first scope review specifically on photodynamic therapy for the treatment of sporotrichosis. A systematic electronic search was conducted in two databases: Web of Science and PubMed. Seven original articles published from 2010 to July 2021 were selected, six of which met the proposed inclusion and exclusion criteria and were considered in this scoping review. Concerning the photoinactivation of Sporothrix spp. the results have been promising as studies, in both animals and humans, have reported significant clinical and mycological effects. The most used photosensitizers were methylene blue and its derivatives, and aminolevulinic acid and its methyl derivative, methyl aminolevulinic acid. In conclusion, photodynamic therapy has great potential in treatment of sporotrichosis, as its fungicidal effect both in vitro and in vivo has clearly been demonstrated. Photodynamic therapy could be used in conjunction with classic antifungal agents to optimize treatment outcomes.

Photodynamic disinfection of SARS-CoV-2 clinical samples using a methylene blue formulation

Abstract

The amplitude of the coronavirus disease 2019 (COVID-19) pandemic motivated global efforts to find therapeutics that avert severe forms of this illness. The urgency of the medical needs privileged repositioning of approved medicines. Methylene blue (MB) has been in clinical use for a century and proved especially useful as a photosensitizer for photodynamic disinfection (PDI). We describe the use of MB to photo-inactivate SARS-CoV-2 in samples collected from COVID-19 patients. One minute of treatment can reduce the percentage inhibition of amplification by 99.99% under conditions of low cytotoxicity. We employed a pseudotyped lentiviral vector (LVs) encoding the luciferase reporter gene and exhibiting the S protein of SARS-CoV-2 at its surface, to infect human ACE2-expressing HEK293T cells. Pre-treatment of LVs with MB-PDI prevented infection at low micromolar MB concentrations and 1 min of illumination. These results reveal the potential of MB-PDI to reduce viral loads in the nasal cavity and oropharynx in the early stages of COVID-19, which may be employed to curb the transmission and severity of the disease.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43630-022-00202-6.

Singlet oxygen generation in aerosol jet and on biological surfaces

The paper presents steady-state and time-resolved experiments on photophysical processes associated with photodynamic inactivation of infections provided by nebulization of Radachlorin photosensitizer solution. As models of surfaces subjected to photodynamic inactivation we used glass, plant leaf, mushroom cap peel and superficial fascia of chicken and salmon skin flaps. The oxygen content in the photosensitizer solution was varied by blowing with atmospheric air and with pure oxygen. It was shown that singlet oxygen was generated efficiently in the aerosol jet and that its amount increased noticeably at higher oxygen concentrations. The kinetics of photosensitizer photobleaching on different surfaces were found to be significantly different with characteristic decay times varying from seconds for leaf and glass to minutes for fascial flaps. This observation was attributed to much faster oxygen depletion on rough crumbly surfaces of biological samples due to effective oxidation reactions occurred. The singlet oxygen generation and degradation times, and the relative quantum yield were determined on different surfaces by recording time-resolved phosphorescence at about 1270 nm under normoxic and hyperoxic conditions and analyzed on the basis of the set of master equations. The results obtained provide reference marks for choosing optimal irradiation durations for photodynamic inactivation of pathogenic infectious agents (bacteria, mycobacteria, fungi, viruses) on mucous membranes, including the tracheobronchial tree.

coli photodynamic inactivation by phthalocyanines in a high molarity buffer solution

Antimicrobial therapy, especially inactivation of multi-antibiotic-resistant strains, requires creating new approaches for drug action and targeted delivery in different environmental conditions. In this work, detonation nanodiamonds (DNDs) were used to deliver polycationic zinc phthalocyanines to E. coli cells. It is shown that in aqueous solutions, zinc phthalocyanines with cholinyl peripheral substituents form complexes with negatively charged DND based on electrostatic interactions. About 40-70 phthalocyanine molecules can bind to a single DND particle, depending on the number of charged groups of the dye molecule. During the complex formation, quenching of phthalocyanine fluorescence and a decrease in its ability to generate reactive oxygen species were observed. In the presence of bacterial cells, phthalocyanine left the complex and induced a photodynamic effect, the magnitude of which depended on the phthalocyanine charge, the molarity of the buffer solution, and the stoichiometry of the phthalocyanine-DND complex. It was found that at physiological values of the ionic strength of the solution, the photodynamic effect of phthalocyanine with a charge of 8+ in combination with a DND is higher than that of the initial phthalocyanine. Thus, nanodiamonds are a promising platform for the delivery of photosensitizers in antimicrobial therapy.

Influence of temperature and relative humidity on the antifungal effect of 405 nm LEDs against Botrytis cinerea and Rhizopus stolonifer and their inactivation on strawberries and tomatoes

In recent years, photodynamic inactivation (PDI) has emerged as a promising preservation method to complement refrigeration in the fresh produce supply chain. However, due to infrastructural limitations in the supply chain, fresh produce is often exposed to environmental conditions rather than recommended storage conditions. Hence, this study aimed to investigate the influence of two important environmental variables in the fresh produce supply chain - temperature and relative humidity (RH), on the PDI of fruit spoilage molds. It also aimed to demonstrate proof-of-concept of their inactivation on fruit surfaces. In the in vitro stage, Botrytis cinerea and Rhizopus stolonifer, the two molds selected for this study, were illuminated with 405 nm LEDs on Dichloran Rose-Bengal Chloramphenicol (DRBC) agar at three levels of temperature (7, 16 and 25 °C) and relative humidity (40, 60 and 80%). Illumination under these conditions caused reductions greater than 94% in the mold populations, at all temperatures and relative humidities. Even so, a temperature of 25 °C was observed to be marginally better for the inactivation as compared to 7 and 16 °C, as it necessitated the lowest dose (6-7 kJ) for the first log reduction of both the molds. Similarly, an RH of 40% worked slightly better for the inactivation of B. cinerea, as it induced inactivation without any lag phase and required the lowest dose (8.03 kJ) for the first log reduction. When the antifungal effect was investigated on fruit surfaces, it was discovered that the illumination reduced the populations of B. cinerea and R. stolonifer on strawberries by 67% and 19%, whereas on tomatoes, the respective inactivations were 79% and 70% respectively. These results demonstrate further promise of PDI as a postharvest technology for reducing the risk of fruit spoilage. This study is also the first to demonstrate the potential of PDI to add value to supply chains where compliance to ideal storage conditions is not feasible.

Ultra-efficient antimicrobial photodynamic inactivation system based on blue light and octyl gallate for ablation of planktonic bacteria and biofilms of Pseudomonas fluorescens

Pseudomonas fluorescens is a Gram-negative spoilage bacterium and dense biofilm producer, causing food spoilage and persistent contamination. Here, we report an ultra-efficient photodynamic inactivation (PDI) system based on blue light (BL) and octyl gallate (OG) to eradicate bacteria and biofilms of P. fluorescens. OG-mediated PDI could lead to a > 5-Log reduction of viable cell counts within 15 min for P. fluorescens. The activity is exerted through rapid penetration of OG towards the cells with the generation of a high-level toxic reactive oxygen species triggered by BL irradiation. Moreover, OG plus BL irradiation can efficiently not only prevent the formation of biofilms but also scavenge the existing biofilms. Additionally, it was shown that the combination of OG/poly(lactic acid) electrospun nanofibers and BL have great potential as antimicrobial packagings for maintaining the freshness of the salamander storge. These prove that OG-mediated PDI can provide a superior platform for eradicating bacteria and biofilm.

Charge density distribution effect in pyrrolidine-fused chlorins on microbial uptake and antimicrobial photoinactivation of microbial pathogens

Two novels structurally related pyrrolidine-fused chlorins were synthesized from 5,10,15,20-tetrakis(pentafluorophenyl)chlorin by nucleophilic aromatic substitution of the para-fluoro groups. The reaction with 2-dimethylaminoethanol produced TPCF₁₆-NMe₂ in 77% yield, while TPCF₁₆-NBu was obtained using butylamine in 87% yield. The latter was extensively methylated to form TPCF₁₆-N⁺Bu in 92% yield. The synthetic strategy was designed to compare the effect of charge density distribution on chlorin in the efficacy to induce photodynamic inactivation of pathogens. TPCF₁₆-NMe₂ has five tertiary amines that can acquire positive charges in aqueous medium by protonation. Furthermore, four of the cationic groups are located in amino groups linked to the chlorine macrocycle by an aliphatic structure of two carbon atoms, which gives it greater movement capacity. In contrast, TPCF₁₆-N⁺Bu presents intrinsic positive charges on aromatic rings. Absorption and fluorescence emission properties were not affected by the peripheral substitution on the chlorin macrocycle. Both photosensitizers (PSs) were able to form singlet molecular oxygen and superoxide anion radical in solution. Uptake and photodynamic inactivation mediated by these chlorins were examined on Staphylococcus aureus and Escherichia coli. Both phototherapeutic agents produced efficient photoinactivation of S. aureus. However, only TPCF₁₆-NMe₂ was rapidly bound to E. coli cells and this chlorin was effective to photoinactivate both strains of bacteria using lower concentrations and shorter irradiation periods. Our outcomes reveal that the charge density distribution is a key factor to consider in the development of new PSs. Accordingly, this work stands out as a promising starting point for the design of new tetrapyrrolic macrocycles with application in PDI.

Amphiphilic tricationic Zn(II)phthalocyanine provides effective photodynamic action to eradicate broad-spectrum microorganisms

A novel tricationic Zn(II)phthalocyanine derivative, (NCH₃)₃ZnPc³⁺, was synthesized by ring expansion reaction of boron(III) [2,9(10),16(17)-trinitrosubphthalocyaninato]chloride. First, the reaction of this subphthalocyanine with 2,3-naphthalenedicarbonitrile and Zn(CH₃COO)₂ catalyzed by 8-diazabicyclo[5.4.0]undec-7-ene was used to obtain the A₃B-type nitrophthalocyanine. After reduction of nitro groups with Na₂S and exhaustive methylation of amino groups, (NCH₃)₃ZnPc³⁺ was formed in good yields. In addition, the tetracationic analog (NCH₃)₄ZnPc⁴⁺ was synthesized to compare their properties. The absorption and fluorescence spectra showed the Q-bands and the red emission, respectively, which are characteristic of the Zn(II)phthalocyanine derivatives in N,N-dimethylformamide. Furthermore, photodynamic activity sensitized by these compounds was studied in the presence of different molecular probes to sense the formation of reactive oxygen species. (NCH₃)₃ZnPc³⁺ efficiently produced singlet molecular oxygen and also it sensitized the formation of superoxide anion radical in the presence of NADH, while the photodynamic activity of (NCH₃)₄ZnPc⁴⁺ was very poor, possibly due to the partial formation of aggregates. Furthermore, the decomposition of L-tryptophan induced by (NCH₃)₃ZnPc³⁺ was mainly mediated by a type II mechanism. Antimicrobial photodynamic inactivation sensitized by these phthalocyanines was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans, as representative microbial cells. In cell suspensions, (NCH₃)₃ZnPc³⁺ was rapidly bound to microbial cells, showing bioimages with red fluorescence emission. After 5 min of irradiation with visible light, (NCH₃)₃ZnPc³⁺ was able to completely eliminate S. aureus, E. coli and C. albicans, using 1.0, 2.5 and 5.0 μM phthalocyanine, respectively. In contrast, a low photoinactivation activity was found with (NCH₃)₄ZnPc⁴⁺ as a photosensitizer. Therefore, the amphiphilic tricationic phthalocyanine (NCH₃)₃ZnPc³⁺ is a promising photosensitizing structure for application as a broad-spectrum antimicrobial phototherapeutic agent.

Photodynamic potential of curcumin in bioadhesive formulations: Optical characteristics and antimicrobial effect against biofilms

BACKGROUND

Although Curcumin (CUR) has great potential as a photosensitizer, the low solubility in water impairs its clinical performance in photodynamic inactivation (PDI). This study sought to establish an effective antimicrobial protocol for PDI using CUR in three different bioadhesive formulations.

METHODS

A CUR-loaded chitosan hydrogel with a poloxamer (CUR-CHIH), a CUR-loaded liquid crystal precursor system (CUR-LCP), a CUR-loaded microemulsion (CUR-ME), and CUR in dimethylsulfoxide (DMSO) solution (CUR-S; control formulation) were tested against in vitro and in situ oral biofilms. The optical properties of each formulation were evaluated.

RESULTS

All of the formulations exhibited lower absorbance than CUR-S; however, the CUR-LCP curve bore the highest resemblance. The CUR present in all formulations was completely degraded after 15 min of illumination. In vitro experiments showed that CUR-S was the only formulation able to significantly reduce biofilm viability of Candida albicans and Lactobacillus casei when compared to the negative control (no PDI); the amount of reduction obtained was 1.8 and 3.7 log (CFU/mL) for C. albicans and L. casei, respectively. There was a significant reduction on the viability of Streptococcus mutans biofilms when CUR-S and CUR-LCP were applied (approximately 3.5 and 1.6 log [CFU/mL], respectively). In situ testing showed antimicrobial efficacy against S. mutans and general microorganisms.

CONCLUSIONS

Although the evaluated protocols has not been effective to all of the evaluated microorganisms, PDI showed potential against dental biofilms and evidence that the phototoxic effects of CUR have a high relation with the type of formulation in which it is loaded.

Assessing the photodynamic efficacy of different photosensitizer-light treatments against foodborne bacteria based on the number of absorbed photons

Increasing interests in photodynamic treatment (PDT) for food preservation require a holistic method to evaluate and compare different photosensitizer (PS)-light treatments. In this report, the absorbed photons were used as the basis to assess the antimicrobial photodynamic efficacy of two PSs, chlorophyllin sodium magnesium salt (Chl-Mg) and chlorophyllin sodium copper salt (Chl-Cu), under blue and white light against two typical foodborne pathogens, Gram-negative Escherichia coli, and Gram-positive Staphylococcus aureus. The results showed that the phototoxicity of a PS was predominantly decided by the absorbed photons rather than the characteristics of light sources. Photosensitized Chl-Mg exhibited superior antimicrobial activity as compared to that of ChlCu. The applied treatments were found to be more effective against S. aureus than E. coli. Bacterial inactivation kinetics as a function of the number of absorbed photons could be described by Weibull model with R² from 0.947-0.962, and kinetics constants D in the range of 0.202 × 10¹⁷ photons/cm²-2.409 × 10¹⁸ photons/cm². The kinetics models may find promising applications in the design, assessment, and optimization of PDT processes.

Emerging trends in the photodynamic inactivation (PDI) applied to the food decontamination

The food and drink manufacturing industry is constantly seeking for alternative sanitation and disinfection systems that may achieve the same antimicrobial efficiency of conventional chemical sanitisers and at the same time be convenient in terms of energy and water savings. A candidate technology for this purpose is the use of light in combination with photosensitisers (PS) to generate a bioactive effect against microbial agents in a process defined as photodynamic inactivation (PDI). This technology can be applied to the food processing of different food matrices to reduce the microbial load of foodborne pathogens such as bacteria, fungi, viruses and protozoa. Also, the PDI can be exploited to increase the shelf-life period of food by inactivation of spoiling microbes. This review analyses new developments in the last five years for PDI systems applied to the food decontamination from foodborne pathogens. The photosensitisation mechanisms and methods are reported to introduce the applied technology against microbial targets in food matrices. Recent blue light emitting diodes (LED) lamp systems for the PDI mediated by endogenous PS are discussed as well PDI technologies with the use of exogenous PS from plant sources such as curcumin and porphyrin-based molecules. The updated overview of the most recent developments in the PDI technology both in wavelengths and employed PS will provide further points of analysis for the advancement of the research on new competitive and effective disinfection systems in the food industry.

Conjugation-regulating synthesis of high photosensitizing activity porphyrin-based covalent organic frameworks for photodynamic inactivation of bacteria

Preparation of porphyrin-based covalent organic frameworks (Por-COFs) with high photosensitizing activity for photodynamic inactivation of bacteria is of great challenge, but significant for economy and human health. Herein, we show a conjugation-regulating strategy to design and synthesize Por-COFs with high photosensitizing activity for the photodynamic inactivation of bacteria. Terephthalaldehyde (Da), 2,5-Dihydroxyterephthalaldehyde (Dha), and 2,5-Diethoxyterephthalaldehyde (Deta) with different conjugation degrees are selected to condense with 5,10,15,20-Tetrakis(4-aminophenyl)porphyrin (Tph) to synthesize COF-366, DhaTph, and JNU-2, respectively. The higher conjugation of Dha and Deta than Da leads to the higher conjugation of DhaTph and JNU-2, respectively. Moreover, the hydroxyl group in Dha and the ethoxy group in Deta further expand the conjugation of DhaTph and JNU-2 via the formation of intralayer extended π-cloud delocalization and p-π conjunction, respectively. The extension of conjugation for DhaTph and JNU-2 results in the increase of intersystem crossing process and significantly improves their photosensitizing activity. Furthermore, JNU-2 with the highest photosensitizing activity exhibits superior antibacterial effects toward Staphylococcus aureus (99.1%) and Escherichia coli (96.8%). This study offers a new conjugation-regulating strategy for designing high photosensitizing activity of Por-COFs for the inactivation of bacteria.

Photoinactivation of mycobacteria to combat infection diseases: current state and perspectives

Abstract

The spread of multi-drug-resistant bacterial strains causing serious infectious diseases dictates the development of new approaches to combat these diseases. In addition to drug resistance, the important causative agent of tuberculosis (Mycobacterium tuberculosis (Mtb)) is able to persist asymptomatically in individuals for many years, causing latent forms of tuberculosis. In such a dormant state, Mtb cells are also resistant to known antibiotics. In this regard, photodynamic inactivation (PDI) could be an effective alternative to antibiotics as its action is based on the generation of active forms of oxygen independently on the presence of specific antibiotic targets, thereby inactivating both drug-resistant and dormant bacteria. In this review, we summarise examples of the application of PDI for the elimination of representatives of the genus Mycobacteria, both in vitro and in vivo. According to published results, including photosensitisers in the PDI regime results in a significantly higher lethal effect. Such experiments were mainly performed using chemically synthesised photosensitisers, which need to be transported to the areas of bacterial infections, limiting PDI usage by surface (skin) diseases. In this regard, endogenous photosensitisers (mainly porphyrins) could be used to solve the problem of transportation. In vitro experiments demonstrate the effective application of PDI for mycobacteria, including Mtb, using endogenous porphyrins; the intracellular contents of these substances can be elevated by administration of 5-aminolevulenic acid, a precursor of porphyrin synthesis. Photodynamic inactivation can also be used for dormant mycobacteria, which are characterised by high levels of endogenous porphyrins. Thus, PDI can effectively eliminate drug-resistant mycobacteria. The exploitation of modern light-transmitting techniques opens new possibilities to use PDI in clinical settings.

Key points

•The potential effects of photodynamic inactivation of mycobacteria are critically reviewed.

•Approaches to photoinactivation of mycobacteria using exogenous and endogenous photosensitisers are described.

•Prospects for the use of photodynamic inactivation in the treatment of tuberculosis are discussed.

Methylene blue-mediated antimicrobial photodynamic therapy can be a novel non-antibiotic platform for bovine digital dermatitis

BACKGROUND

Bovine digital dermatitis (BDD) is one of the most important diseases that effect dairy cows. Methylene blue-mediated antimicrobial photodynamic therapy (MB-APDT) emerges as a promising technique to treat superficial infections in bovines.

METHODS

Twenty BDD lesions located at the skin horn transition of the claw of pelvic limbs of 16 cows were treated by MB-APDT, using a red LED cluster (λ = 660 nm, irradiance =60 mW/cm², exposure time = 40 s) combined with topical application of MB at 0.01 %; or by topical application of OXY (500 mg in 20 % solution). Each lesion was treated twice with an interval of 14 days. Lesions were weekly evaluated until day 28 by clinical analysis and by histological examination on days 0 and 28.

RESULTS

Both treatments led to a similar reduction of lesions area. At day 28, three lesions treated by OXY did not present completely recovery, whereas no lesions were observed in MB-APDT group. OXY resulted in a slight increase in type I and III collagen levels, while MB-APDT led to a significant increase in the total area of both collagen types. An abundant number of spirochetes were histologically observed in all lesions before treatments. On the 28th day, five lesions treated by OXY still presented a slight number of spirochetes, whereas in MB-APDT group no spirochetes were evidenced.

CONCLUSION

Our findings suggest that MB-APDT is more effective than OXY and could be used in Veterinary practice to fight BDD.

Antimicrobial activity of 405 nm light-emitting diode (LED) in the presence of riboflavin against Listeria monocytogenes on the surface of smoked salmon

This study investigated the antimicrobial activity of 405 nm light-emitting diode (LED) with and without riboflavin against Listeria monocytogenes in phosphate buffered saline (PBS) and on smoked salmon at different storage temperatures and evaluated its impact on food quality. The results show that riboflavin-mediated LED illumination in PBS 25 °C significantly inactivated L. monocytogenes cells by 6.2 log CFU/mL at 19.2 J/cm², while illumination alone reduced 1.9 log CFU/mL of L. monocytogenes populations at 57.6 J/cm². L. monocytogenes populations on illuminated smoked salmon decreased by 1.0-2.2 log CFU/cm² at 1.27-2.76 kJ/cm² at 4, 12, and 25 °C, regardless of the presence of riboflavin. Although illumination with and without riboflavin caused the lipid peroxidation and color change in smoked salmon, this study demonstrates the potential of a 405 nm LED to preserve the smoked salmon products, reducing the risk of listeriosis.

A novel tricationic fullerene C60 as broad-spectrum antimicrobial photosensitizer: mechanisms of action and potentiation with potassium iodide

A novel amphiphilic photosensitizing agent based on a tricationic fullerene C₆₀ (DMC₆₀³⁺) was efficiently synthesized from its non-charged analogue MMC₆₀. These fullerenes presented strong UV absorptions, with a broad range of less intense absorption up to 710 nm. Both compounds showed low fluorescence emission and were able to photosensitize the production of reactive oxygen species. Furthermore, photodecomposition of L-tryptophan sensitized by both fullerenes indicated an involvement of type II pathway. DMC₆₀³⁺ was an effective agent to produce the photodynamic inactivation (PDI) of Staphylococcus aureus, Escherichia coli and Candida albicans. Mechanistic insight indicated that the photodynamic action sensitized by DMC₆₀³⁺ was mainly mediated by both photoprocesses in bacteria, while a greater preponderance of the type II pathway was found in C. albicans. In presence of potassium iodide, a potentiation of PDI was observed due to the formation of reactive iodine species. Therefore, the amphiphilic DMC₆₀³⁺ can be used as an effective potential broad-spectrum antimicrobial photosensitizer.

Pentamidine enhances photosensitization of Acinetobacter baumannii using diode lasers with emission of light at wavelength of ʎ = 405 nm and ʎ = 635 nm

Antimicrobial photodynamic inactivation is currently one of the most promising trends in the modern bactericidal protocols. Under the conditions defined in our studies, we found that in vitro photosensitization of A. baumannii with 5-ALA as a precursor of protoporphyrin IX (photosensitizer) reduces the concentration of viable cells in planktonic cultures, and this process can be strongly enhanced by pentamidine. Diode lasers with the peak-power wavelength of ʎ = 405 nm (radiation intensity of 26 mW cm^-2) and ʎ = 635 nm (radiation intensity of 55 mW cm^-2) were used in this study. It was found that a blue laser light (energy fluence of 64 J cm^-2; no external photosensitizer) in the presence of pentamidine resulted in a reduction of CFU of 99.992 % compared to 99.97 % killing without pentamidine. When a red laser light was used in the experiments (energy fluence of 136 J cm^-2; no external photosensitizer), the mortality rate was 99.98 % in the presence of pentamidine compared to 99.93 % of those killed without the addition of this drug. The lethal effect with 5-ALA was achieved under blue light fluence of 16 J cm^-2 (in the presence of pentamidine) and 32 J cm^-2 (without pentamidine). In the case of laser light of 635 nm, the lethal effect with 5-ALA was attained with energy fluence of 51 J cm^-2 (with pentamidine) and 102 J cm^-2 (without pentamidine). The possible roles of pentamidine in enhancing photodynamic inactivation of A. baumannii have been discussed.

Photodynamic inactivation of Staphylococcus aureus using tetraethylene glycol-substituted Zn(II) phthalocyanine

Methicillin resistant Staphylococcus aureus infections are increasing, especially in intensive care units. A new method for photodynamic inactivation (PDI) generates reactive oxygen species by photosensitization to kill bacteria. We investigated the PDI effect of tetraethylene glycol-substituted Zn(II) phthalocyanine (TEG-P) on S. aureus strains including two standards (ATCC 25923 and ATCC 43400) and 20 clinically isolated methicillin sensitive and 20 methicillin resistance strains. We also investigated three treated groups: 650 nm laser only, TEG-P only and TEG-P + laser, plus one control group. Treatments included 0.5, 1, 2, 4, 8, 16, 32 µg/ml concentrations of TEG-P. No suppression of bacterial growth was observed in the control, laser only and TEG-P only groups whether or not S. aureus was methicillin resistant. Bacterial growth was suppressed by 85% using 8 µg/ml TEG-P and completely suppressed by 32 µg/ml TEG-P in the TEG-P + laser group. A combination of TEG-P + laser treatment may be an alternative to conventional antibiotics for routine treatment of S. aureus infections, although further investigation of the effect at the tissue level is required.

Increased photoinactivation stress tolerance of Streptococcus agalactiae upon consecutive sublethal phototreatments

Streptococcus agalactiae (Group B Streptococcus, GBS) is a common commensal bacterium in adults but remains a leading source of invasive infections in newborns, pregnant women, and the elderly, and more recently, causes an increased incidence of invasive disease in nonpregnant adults. Reduced penicillin susceptibility and emerging resistance to non-β-lactams pose challenges for the development and implementation of novel, nonantimicrobial strategies to reduce the burden of GBS infections. Antimicrobial photodynamic inactivation (aPDI) via the production of singlet oxygen or other reactive oxygen species leads to the successful eradication of pathogenic bacteria, affecting numerous cellular targets of microbial pathogens and indicating a low risk of resistance development. Nevertheless, we have previously reported possible aPDI tolerance development upon repeated sublethal aPDI applications; thus, the current work was aimed at investigating whether aPDI tolerance could be observed for GBS and what mechanisms could cause it. To address this problem, 10 cycles of sublethal aPDI treatments employing rose bengal as a photosensitizer, were applied to the S. agalactiae ATCC 27956 reference strain and two clinical isolates (2306/02 and 2974/07, serotypes III and V, respectively). We demonstrated aPDI tolerance development and stability after 5 cycles of subculturing with no aPDI exposure. Though the treatment resulted in a stable phenotype, no increases in mutation rate or accumulated genetic alterations were observed (employing a RIF-, CIP-, STR-resistant mutant selection assay and cyl sequencing, respectively). qRT-PCR analysis demonstrated that 10 sublethal aPDI exposures led to increased expression of all tested major oxidative stress response elements; changes in sodA, ahpC, npx, cylE, tpx and recA expression indicate possible mechanisms of developed tolerance. Increased expression upon sublethal aPDI treatment was reported for all but two genes, namely, ahpC and cylE. aPDI targeting cylE was further supported by colony morphology changes induced with 10 cycles of aPDI (increased SCV population, increased hemolysis, increased numbers of dark- and unpigmented colonies). In oxidant killing assays, aPDI-tolerant strains demonstrated no increased tolerance to hypochlorite, superoxide (paraquat), singlet oxygen (new methylene blue) or oxidative stress induced by aPDI employing a structurally different photosensitizer, i.e., zinc phthalocyanine, indicating a lack of cross resistance. The results indicate that S. agalactiae may develop stable aPDI tolerance but not resistance when subjected to multiple sublethal phototreatments, and this risk should be considered significant when defining efficient anti-S. agalactiae aPDI protocols.

Screening of antimicrobial synergism between phenolic acids derivatives and UV-A light radiation

The objective of this study was to investigate synergistic antibacterial activity based on a combination of UV-A light and three classes of food grade compounds: benzoic acid derivatives, cinnamic acid derivatives, and gallates. By using Escherichia coli O157:H7 as the model strain, it was observed that three cinnamic acid derivatives (ferulic acid, coumaric acid, and caffeic acid) and one benzoic acid derivative (2,5-dihydroxybenzoic acid) presented strong synergistic antibacterial activity with UV-A light radiation, where 1 mM levels of these compounds plus with 15 min of UV-A light (total light dose of 6.1 cm^-2) led to more than 7-log CFU mL^-1 of bacterial inactivation. In contrast, synergistic antibacterial activity between UV-A light and most benzoic acid derivatives (benzoic acid, gallic acid, vanillic acid, and 2,5-dimethoxybenzoic acid) were only observed after higher concentrations of these compounds were applied (10 mM). Lastly, from the three gallates tested (methyl gallate, ethyl gallate, and propyl gallate), only propyl gallate showed strong antibacterial synergism with UV-A light, where 10 mM of propyl gallate plus 15 min of UV-A light led to approximately 6.5-log of bacterial reduction. Presence of antioxidant compounds mitigated the light-mediated antibacterial activity of gallic acid, 2,5-dihydroxybenzoic acid, and propyl gallate. Similarly, the light-mediated antibacterial activity of these compounds was significantly (P < 0.05) reduced against metabolic-inhibited bacterial cells (sodium azide pretreatment). On the other hand, the antibacterial synergism between ferulic acid and UV-A light was not affected by the presence of antioxidants or the metabolic state of the bacterial cells. Due to the increasing concerns of antimicrobial resistant (AMR) pathogens, the study also investigated the proposed synergistic treatment on AMR Salmonella. Combinations of 1 mM of ferulic acid or 1 mM of 2,5-dihydroxybenzoic acid with UV-A light radiation was able to inactivate more than 6-log of a multi-drug resistant Salmonella Typhimurium strain.

Immobilization of alkyl-pterin photosensitizer on silicon surfaces through in situ SN2 reaction as suitable approach for photodynamic inactivation of Staphylococcus aureus

The tuning of surface properties through functionalization is an important field of research with a broad spectrum of applications. Self-assembled monolayers (SAMs) allow the surface tailoring through the adsorption of molecular layers having the appropriate functional group or precursor group enabling in situ chemical reactions and thus to the incorporation of new functionalities. The latter approach is particularly advantageous when the incorporation of huge groups is needed. In this study, we report the immobilization of pterin moieties on 11-bromoundecyltrichlorosilane-modified silicon substrates based on the in situ replacement of the bromine groups by pterin (Ptr), the parent derivative of pterins, by means of a nucleophilic substitution reaction. The modified surface was structurally characterized through a multi-technique approach, including high-resolution XPS analysis, contact angle measurements, and AFM. The designed synthesis method leads to the functionalization of the silicon surface with two compounds, O-undecyl-Ptr and N-undecyl-Ptr, with a higher proportion of the N-derivative (1:8 ratio). The alkyl-pterins immobilized via the proposed strategy, retain their photochemical properties, being able to inhibit Staphylococcus aureus growth under irradiation (84.3 ± 15.6 % reduction in viable cells). Our results open the possibility for the modification of several materials, such as glass and metal, through the formation of SAMs having the proper head group, thus allowing the design of photosensitive surfaces with potential microbiological self-cleaning properties.