Photodynamic inactivation of bacterial and yeast biofilms with a cationic porphyrin

Systemic Effects of Photoactivated 5,10,15,20-tetrakis(N-methylpyridinium-3-yl) Porphyrin on Healthy Drosophila melanogaster

Porphyrins are frequently employed in photodynamic therapy (PDT), a non-invasive technique primarily utilized to treat subcutaneous cancers, as photosensitizing agents (PAs). The development of a new PA with improved tissue selectivity and efficacy is crucial for expanding the application of PDT for the management of diverse cancers. We investigated the systemic effects of 5,10,15,20-tetrakis(N-methylpyridinium-3-yl)-porphyrin (TMPyP3) using Drosophila melanogaster adult males. We established the oral administration schedule and demonstrated that TMPyP3 was absorbed and stored higher in neuronal than in non-neuronal extracts. Twenty-four hours after oral TMPyP3 photoactivation, the quantity of hydrogen peroxide (H2O2) increased, but exclusively in the head extracts. Regardless of photoactivation, TMPyP3 resulted in a reduced concentration of H2O2 after 7 days, and this was linked with a decreased capacity to climb, as indicated by negative geotaxis. The findings imply that systemic TMPyP3 therapy may disrupt redox regulation, impairing cellular signaling and behavioral outcomes in the process. To determine the disruptive effect of porphyrins on redox homeostasis, its duration, and the mechanistic variations in retention across various tissues, more research is required.

Fungal biofilm formation and its regulatory mechanism

Fungal biofilm is a microbial community composed of fungal cells and extracellular polymeric substances (EPS). In recent years, fungal biofilms have played an increasingly important role in many fields. However, there are few studies on fungal biofilms and their related applications and development are still far from enough. Therefore, this review summarizes the composition and function of EPS in fungal biofilms, and improves and refines the formation process of fungal biofilms according to the latest viewpoints. Moreover, based on the study of Saccharomyces cerevisiae and Candida albicans, this review summarizes the gene regulation network of fungal biofilm synthesis, which is crucial for systematically understanding the molecular mechanism of fungal biofilm formation. It is of great significance to further develop effective methods at the molecular level to control harmful biofilms or enhance and regulate the formation of beneficial biofilms. Finally, the quorum sensing factors and mixed biofilms formed by fungi in the current research of fungal biofilms are summarized. These results will help to deepen the understanding of the formation process and internal regulation mechanism of fungal biofilm, provide reference for the study of EPS composition and structure, formation, regulation, group behavior and mixed biofilm formation of other fungal biofilms, and provide strategies and theoretical basis for the control, development and utilization of fungal biofilms.

Evaluation of quantification methods to determine photodynamic action on mono- and dual-species bacterial biofilms

The effect of photodynamic inactivation (PDI) sensitized by 5,10,15,20-tetra(4-N,N,N-trimethylammoniophenyl)porphyrin (TMAP4+) on different components of mono- and dual-species biofilms of Staphylococcus aureus and Escherichia coli was determined by different methods. First, the plate count technique showed that TMAP4+-PDI was more effective on S. aureus than E. coli biofilm. However, crystal violet staining revealed no significant differences between before and after PDI biofilms of both bacteria. On the other hand, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method indicated a reduction in viable cells as the light exposure time increases in both, mono- and dual-species biofilms. Furthermore, it was determined that as the irradiation time increases, the amount of extracellular polymeric substances present in the biofilms decreased. This effect was presented in both strains and in the mixed biofilm, being more evident in S. aureus mono-specie biofilm. Finally, scanning electron microscopy analysis showed a decrease in the number of cells forming the biofilm after photosensitization treatments. This information makes it possible to determine whether the photodynamic action is based on damage to metabolic activity, extracellular matrix and/or biomass, which may be useful in establishing a fully effective PDI protocol for the treatment of microorganisms growing as biofilms.

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.

Mechanisms of antibiotic resistance in Pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa is a major cause of life-threatening acute infections and life-long lasting chronic infections. The characteristic biofilm mode of life in P. aeruginosa chronic infections severely limits the efficacy of antimicrobial therapies, as it leads to intrinsic tolerance, involving physical and physiological factors in addition to biofilm-specific genes that can confer a transient protection against antibiotics promoting the development of resistance. Indeed, a striking feature of this pathogen is the extraordinary capacity to develop resistance to nearly all available antibiotics through the selection of chromosomal mutations, evidenced by its outstanding and versatile mutational resistome. This threat is dramatically amplified in chronic infections, driven by the frequent emergence of mutator variants with enhanced spontaneous mutation rates. Thus, this mini review is focused on describing the complex interplay of antibiotic resistance mechanisms in P. aeruginosa biofilms, to provide potentially useful information for the design of effective therapeutic strategies.

The effect of photodynamic therapy in controlling the oral biofilm: A comprehensive overview

Several resistance mechanisms are involved in dental caries, including oral biofilms. An accumulation of bacteria on the surface of teeth is called plaque. Periodontitis and gingivitis are caused by dental plaque. In this review article, we aimed to review the studies associated with the application of photodynamic therapy (PDT) to prevent and treat various microbial biofilm-caused oral diseases in recent decades. There are several studies published in PubMed that have described antimicrobial photodynamic therapy (APDT) effects on microorganisms. Several in vitro and in vivo studies have demonstrated the potential of APDT for treating endodontic, periodontal, and mucosal infections caused by bacteria as biofilms. Reactive oxygen species (ROS) are activated in the presence of oxygen by integrating a nontoxic photosensitizer (PS) with appropriate wavelength visible light. By causing irreversible damage to microorganisms, ROS induces some biological and photochemical events. Testing several wavelengths has been conducted to identify potential PS for APDT. A standard protocol is not yet available, and the current review summarizes findings from dental studies on APDT.

Photodynamic therapy for ESKAPE pathogens: An emerging approach to combat antimicrobial resistance (AMR)

The increase in antimicrobial resistance, particularly in ESKAPE pathogens, has resulted in the dire need for new therapeutic approaches. ESKAPE is an acronym for a group of bacteria that are responsible for a majority of nosocomial and community acquired infections. The acronym stands for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species. These pathogens are known for their ability to develop resistance to multiple antibiotics, making them difficult to treat thus posing a significant threat to public health. In light of the alarming consequences of antimicrobial resistance, it has been estimated that, in the absence of a substantial increase in the rate of development of new effective drugs, the number of casualties related to these infections will increase from about 700,000 in 2016 up to nearly 10,000,000 in 2050 [1]. One potential strategy to treat these pathogens is photodynamic therapy (PDT). In the early 20th century, Oscar Raab observed the phototoxicity of acridine red against Paramecium caudatum, while Tappenier and Jesionek demonstrated the photodynamic effects of eosin for treating cutaneous diseases. These discoveries laid the foundation for Photodynamic Therapy (PDT), which utilizes a non-toxic photosensitizer (PS) followed by targeted light irradiation for treatment [2]. PDT involves the use of a photosensitizer, a light source, and oxygen to eliminate highly active infectious pathogens such as bacteria, viruses, and fungi. PDT is known to possess several advantages including localized treatment and fewer side effects. Various photosensitizers and light sources have been assessed in different strains, showing promising results suggesting PDT to be a promising potential treatment option. PDT utilizes PS compounds with suitable light absorption that showcase effective results against the pathogens in vitro and in vivo, including BODIPY derivatives, Methylene Blue, and other dyes like porphyrin derivatives, phthalocyanines, indole derivatives, Photophrin, etc., inhibiting the growth of infections, for both in planktonic cells and in biofilms. Combination of PDT with other therapies like efflux pump inhibitors or quorum sensing inhibitors has also proven to be efficacious. However, this domain further needs to be assessed before it reaches the society.

Pseudomonas aeruginosa: Infections and novel approaches to treatment "Knowing the enemy" the threat of Pseudomonas aeruginosa and exploring novel approaches to treatment

Pseudomonas aeruginosa is an aerobic Gram-negative rod-shaped bacterium with a comparatively large genome and an impressive genetic capability allowing it to grow in a variety of environments and tolerate a wide range of physical conditions. This biological flexibility enables the P. aeruginosa to cause a broad range of infections in patients with serious underlying medical conditions, and to be a principal cause of health care associated infection worldwide. The clinical manifestations of P. aeruginosa include mostly health care associated infections and community-acquired infections. P. aeruginosa possesses an array of virulence factors that counteract host defence mechanisms. It can directly damage host tissue while utilizing high levels of intrinsic and acquired antimicrobial resistance mechanisms to counter most classes of antibiotics. P. aeruginosa co-regulates multiple resistance mechanisms by perpetually moving targets poses a significant therapeutic challenge. Thus, there is an urgent need for novel approaches in the development of anti-Pseudomonas agents. Here we review the principal infections caused by P. aeruginosa and we discuss novel therapeutic options to tackle antibiotic resistance and treatment of P. aeruginosa infections that may be further developed for clinical practice.

Photodynamic inactivation of multidrug-resistant strains of Klebsiella pneumoniae and Pseudomonas aeruginosa in municipal wastewater by tetracationic porphyrin and violet-blue light: The impact of wastewater constituents

There is an increasing need to discover effective methods for treating municipal wastewater and addressing the threat of multidrug-resistant (MDR) strains of bacteria spreading into the environment and drinking water. Photodynamic inactivation (PDI) that combines a photosensitiser and light in the presence of oxygen to generate singlet oxygen and other reactive species, which in turn react with a range of biomolecules, including the oxidation of bacterial genetic material, may be a way to stop the spread of antibiotic-resistant genes. The effect of 5,10,15,20-(pyridinium-3-yl)porphyrin tetrachloride (TMPyP3) without light, and after activation with violet-blue light (VBL) (394 nm; 20 mW/cm2), on MDR strains of Pseudomonas aeruginosa, Klebsiella pneumoniae and K. pneumoniae OXA-48 in tap water and municipal wastewater was investigated. High toxicity (~2 μM) of TMPyP3 was shown in the dark on both strains of K. pneumoniae in tap water, while on P. aeruginosa toxicity in the dark was low (50 μM) and the PDI effect was significant (1.562 μM). However, in wastewater, the toxicity of TMPyP3 without photoactivation was much lower (12.5-100 μM), and the PDI effect was significant for all three bacterial strains, already after 10 min of irradiation with VBL (1.562-6.25 μM). In the same concentrations, or even lower, an anti-adhesion effect was shown, suggesting the possibility of application in biofilm control. By studying the kinetics of photoinactivation, it was found that with 1,562 μM of TMPyP3 it is possible to achieve the complete destruction of all three bacteria after 60 min of irradiation with VBL. This study confirmed the importance of studying the impact of water constituents on the properties and PDI effect of the applied photosensitiser, as well as checking the sensitivity of targeted bacteria to light of a certain wavelength, in conditions as close as possible to those in the intended application, to adjust all parameters and perfect the method.

Antimicrobial photodynamic therapy against oral biofilm: influencing factors, mechanisms, and combined actions with other strategies

Oral biofilms are a prominent cause of a wide variety of oral infectious diseases which are still considered as growing public health problems worldwide. Oral biofilms harbor specific virulence factors that would aggravate the infectious process and present resistance to some traditional therapies. Antimicrobial photodynamic therapy (aPDT) has been proposed as a potential approach to eliminate oral biofilms via in situ-generated reactive oxygen species. Although numerous types of research have investigated the effectiveness of aPDT, few review articles have listed the antimicrobial mechanisms of aPDT on oral biofilms and new methods to improve the efficiency of aPDT. The review aims to summarize the virulence factors of oral biofilms, the progress of aPDT in various oral biofilm elimination, the mechanism mediated by aPDT, and combinatorial approaches of aPDT with other traditional agents.

Smart dental materials for antimicrobial applications

Smart biomaterials can sense and react to physiological or external environmental stimuli (e.g., mechanical, chemical, electrical, or magnetic signals). The last decades have seen exponential growth in the use and development of smart dental biomaterials for antimicrobial applications in dentistry. These biomaterial systems offer improved efficacy and controllable bio-functionalities to prevent infections and extend the longevity of dental devices. This review article presents the current state-of-the-art of design, evaluation, advantages, and limitations of bioactive and stimuli-responsive and autonomous dental materials for antimicrobial applications. First, the importance and classification of smart biomaterials are discussed. Second, the categories of bioresponsive antibacterial dental materials are systematically itemized based on different stimuli, including pH, enzymes, light, magnetic field, and vibrations. For each category, their antimicrobial mechanism, applications, and examples are discussed. Finally, we examined the limitations and obstacles required to develop clinically relevant applications of these appealing technologies.

Domestic LED bulb induced photodynamic effect of Toluidine Blue O-embedded silicone catheters against urinary tract infection

BACKGROUND

Novel combination of Toluidine Blue O (TBO) embedded silicone catheter with domestic/household LED bulb has a potential in clinical infection such as prevention of multi drug resistant catheter-associated urinary tract infections (CAUTIs) through photodynamic therapy.

MATERIAL AND METHODS

Preliminarily, TBO was entrapped into silicone catheter by swell-encapsulation-shrink method. Further, in vitro study was carried out to check the antimicrobial photodynamic efficacy of TBO with domestic/household LED light. Antibiofilm activity was evaluated by scanning electron microscopy.

RESULTS

The results showed that these modified TBO embedded silicone catheters showed significant antimicrobial and antibiofilm activity against vancomycin resistant Staphylococcus aureus VRSA. Small piece (1 cm) of TBO-embedded silicone catheter (700 µM) showed 6 log₁₀ reduction in the viable count when exposed for only 5 min of domestic/household LED bulb, while 1 cm piece of 500 µM and 700 µM concentration of TBO-embedded catheter eradicated all bacterial load when exposed to 15 min of light. Segment of medical grade TBO-embedded silicone catheters were used to carry out investigation of reactive oxygen species generation mainly singlet oxygen that contributes to type II phototoxicity.

CONCLUSION

These modified catheter provides cost effective, easy to manage and less time consuming therapy to eliminate CAUTIs.

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.

Sulfonamide Porphyrins as Potent Photosensitizers against Multidrug-Resistant Staphylococcus aureus (MRSA): The Role of Co-Adjuvants

Sulfonamides are a conventional class of antibiotics that are well-suited to combat infections. However, their overuse leads to antimicrobial resistance. Porphyrins and analogs have demonstrated excellent photosensitizing properties and have been used as antimicrobial agents to photoinactivate microorganisms, including multiresistant Staphylococcus aureus (MRSA) strains. It is well recognized that the combination of different therapeutic agents might improve the biological outcome. In this present work, a novel meso-arylporphyrin and its Zn(II) complex functionalized with sulfonamide groups were synthesized and characterized and the antibacterial activity towards MRSA with and without the presence of the adjuvant KI was evaluated. For comparison, the studies were also extended to the corresponding sulfonated porphyrin TPP(SO₃H)₄. Photodynamic studies revealed that all porphyrin derivatives were effective in photoinactivating MRSA (>99.9% of reduction) at a concentration of 5.0 μM upon white light radiation with an irradiance of 25 mW cm^-2 and a total light dose of 15 J cm^-2. The combination of the porphyrin photosensitizers with the co-adjuvant KI during the photodynamic treatment proved to be very promising allowing a significant reduction in the treatment time and photosensitizer concentration by six times and at least five times, respectively. The combined effect observed for TPP(SO₂NHEt)₄ and ZnTPP(SO₂NHEt)₄ with KI seems to be due to the formation of reactive iodine radicals. In the photodynamic studies with TPP(SO₃H)₄ plus KI, the cooperative action was mainly due to the formation of free iodine (I₂).

In Vitro Photoinactivation of Fusarium oxysporum Conidia with Light-Activated Ammonium Phthalocyanines

Antimicrobial photodynamic therapy (aPDT) has been explored as an innovative therapeutic approach because it can be used to inactivate a variety of microbial forms (vegetative forms and spores) without causing significant damage to host tissues, and without the development of resistance to the photosensitization process. This study assesses the photodynamic antifungal/sporicidal activity of tetra- and octasubstituted phthalocyanine (Pc) dyes with ammonium groups. Tetra- and octasubstituted zinc(II) phthalocyanines (1 and 2) were prepared and tested as photosensitizers (PSs) on Fusarium oxysporum conidia. Photoinactivation (PDI) tests were conducted with photosensitizer (PS) concentrations of 20, 40, and 60 µM under white-light exposure at an irradiance of 135 mW·cm^-2, applied during 30 and 60 min (light doses of 243 and 486 J·cm^-2). High PDI efficiency corresponding to the inactivation process until the detection limit was observed for both PSs. The tetrasubstituted PS was the most effective, requiring the lowest concentration and the shortest irradiation time for the complete inactivation of conidia (40 µM, 30 min, 243 J·cm^-2). Complete inactivation was also achieved with PS 2, but a longer irradiation time and a higher concentration (60 µM, 60 min, 486 J·cm^-2) were necessary. Because of the low concentrations and moderate energy doses required to inactivate resistant biological forms such as fungal conidia, these phthalocyanines can be considered potent antifungal photodynamic drugs.

Photo-Inactivation of Staphylococcus aureus by Diaryl-Porphyrins

Photodynamic Antimicrobial Chemotherapy (PACT) has received great attention in recent years since it is an effective and promising modality for the treatment of human oral and skin infections with the advantage of bypassing pathogens' resistance to antimicrobials. Moreover, PACT applications demonstrated a certain activity in the inhibition and eradication of biofilms, overcoming the well-known tolerance of sessile communities to antimicrobial agents. In this study, 13 diaryl-porphyrins (mono-, di-cationic, and non-ionic) P1-P13 were investigated for their potential as photosensitizer anti-Staphylococcus aureus. The efficacy of the diaryl-porphyrins was evaluated through photo-inactivation tests. Crystal-violet staining combined with viable count techniques were aimed at assaying their anti-biofilm activity. Among the tested compounds, the neutral photosensitizer P4 was better than the cationic ones, irrespective of their corresponding binding rates. In particular, P4 was active in inhibiting the biofilm formation and in impairing the viability of the adherent and planktonic populations of a 24 h old biofilm. The inhibitory activity was also efficient against a methicillin resistant S. aureus strain. In conclusion, the diaryl-porphyrin family represents a reservoir of promising compounds for photodynamic applications against the pathogen S. aureus and in preventing the formation of biofilms that cause many infections to become chronic.

Photo-responsive polymeric micelles for the light-triggered release of curcumin targeting antimicrobial activity

Nanocarriers have been successfully used to solubilize, deliver, and increase the bioavailability of curcumin (CUR), but slow CUR release rates hinder its use as a topical photosensitizer in antimicrobial photodynamic therapy. A photo-responsive polymer (PRP) was designed for the light-triggered release of CUR with an effective light activation-dependent antimicrobial response. The characterization of the PRP was compared with non-responsive micelles comprising Pluronics™ P123 and F127. According to the findings, the PRP formed photo-responsive micelles in the nanometric scale (< 100 nm) with a lower critical micelle concentration (3.74 × 10^-4 M^-1, 5.8 × 10^-4 M^-1, and 7.2 × 10^-6 M^-1 for PRP, F127, P123, respectively, at 25°C) and higher entrapment efficiency of CUR (88.7, 77.2, and 72.3% for PRP, F127, and P123 micelles, respectively) than the pluronics evaluated. The PRP provided enhanced protection of CUR compared to P123 micelles, as demonstrated in fluorescence quenching studies. The light-triggered release of CUR from PRP occurred with UV light irradiation (at 355 nm and 25 mW cm^-2) and a cumulative release of 88.34% of CUR within 1 h compared to 80% from pluronics after 36 h. In vitro studies showed that CUR-loaded PRP was non-toxic to mammal cell, showed inactivation of the pathogenic microorganisms Candida albicans, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus, and decreased biofilm biomass when associated with blue light (455  nm, 33.84 J/cm²). The findings show that the CUR-loaded PRP micelle is a viable option for antimicrobial activity.

Does potassium iodide help in the microbial reduction of oral microcosm biofilms after photodynamic therapy with methylene blue and red laser?

OBJECTIVE

To evaluate the efficacy of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) doped with potassium iodide (KI) against oral microcosms biofilms cultured in dentin.

METHODS

A saliva-glycerol stock formed from pooled human saliva was diluted in McBain artificial saliva with 1% sucrose (1:1), inoculated on bovine dentin blocks, and refreshed daily for 5 days. The biofilms were divided (n = 9/group) and treated with 0.9% NaCl (C), 0.2% chlorhexidine (CX), 0.01% MB + low-power laser 15 J, 88 mW, 180 s (PL), and 0.01% MB + 50 mM KI + laser (PKIL). Serial dilution was performed, and cellular viability (CFU/mL) was evaluated for total microorganisms, total lactobacilli, total streptococci, and S. mutans. Additional biofilms were cultured and treated (n = 4) for biomass determination (%BMR). The microscopic structure of the biofilms was observed by SEM. One-way ANOVA and Tukey tests were conducted (α=5%).

RESULTS

Total microorganisms and total streptococci significantly reduced in biofilms treated with CX and PKIL when compared to C, but the CX, PKIL, and PL treatments did not differ from each other. Total lactobacilli and S. mutans showed a significant reduction in the CX, PL, and PKIL groups when compared to C, but with no difference between them. Biomass analysis showed a significantly reduction for CX and PKIL compared to C. SEM micrographs showed noticeable changes in bacterial membrane integrity for the PKIL and CX groups.

CONCLUSION

The addition of KI to methylene blue-mediated aPDT in microcosm biofilms was effective in reducing oral microorganisms, but the effect was group dependent.

Efficacy of the combination of P5 peptide and photodynamic therapy mediated by bixin and chlorin-e6 against Cutibacterium acnes biofilm

In this study, the action of antimicrobial peptide (AMP) P5 and antimicrobial photodynamic therapy (aPDT) mediated by bixin and chlorin-e6 (Ce6) on Cutibacterium acnes (C. acnes) in planktonic phase and biofilm were evaluated both as monotherapies and combined therapies. Microbial viability after treatments were quantified by colony-forming units per milliliter of the sample (CFU/mL) and have demonstrated that all treatments employed exerted bactericidal activity, reducing the microbial load by more than 3 log₁₀ CFU/mL, also demonstrating for the first time in the literature the antimicrobial photodynamic effect of bixin that occurs mostly through type I mechanism which was proved by the quantification of superoxide anion production. Bacterial biofilm was completely eliminated only after its exposure to aPDT mediated by this PS, however, Ce6 proved to be a more efficient PS, considering that most of the photodynamic effect of bixin- aPDT was exerted by excitation of the endogenous C porphyrins of C. acnes with blue light. The combination of P5 with Ce6-aPDT showed a synergistic effect on the bacterial biofilm with a reduction in microbial load by more than 10 log₁₀ CFU/mL, in which the ability of P5 to permeabilize the polymeric extracellular matrix of the biofilm explains the obtained results, with greater internalization of the PS as shown by the Confocal Laser Scanning Microscopy. One-way ANOVA (Analysis of Variance) with Tukey's post-test and two-way ANOVA with Bonferroni's post-test were used to compare the values of continuous variables between the control group and the treatment groups.

Treatment of Pseudomonas aeruginosa infectious biofilms: Challenges and strategies

Pseudomonas aeruginosa, a Gram-negative bacterium, is one of the major pathogens implicated in human opportunistic infection and a common cause of clinically persistent infections such as cystic fibrosis, urinary tract infections, and burn infections. The main reason for the persistence of P. aeruginosa infections is due to the ability of P. aeruginosa to secrete extracellular polymeric substances such as exopolysaccharides, matrix proteins, and extracellular DNA during invasion. These substances adhere to and wrap around bacterial cells to form a biofilm. Biofilm formation leads to multiple antibiotic resistance in P. aeruginosa, posing a significant challenge to conventional single antibiotic therapeutic approaches. It has therefore become particularly important to develop anti-biofilm drugs. In recent years, a number of new alternative drugs have been developed to treat P. aeruginosa infectious biofilms, including antimicrobial peptides, quorum-sensing inhibitors, bacteriophage therapy, and antimicrobial photodynamic therapy. This article briefly introduces the process and regulation of P. aeruginosa biofilm formation and reviews several developed anti-biofilm treatment technologies to provide new directions for the treatment of P. aeruginosa biofilm infection.

Photodynamic antibacterial and antibiofilm activity of riboflavin against Xanthomonas oryzae pv oryzae: an ecofriendly strategy to combat bacterial leaf blight (BLB) rice disease

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv oryzae (Xoo), is one of the most damaging rice diseases, causing severe production losses depending on the rice variety. The purpose of this study was to develop an antibacterial photodynamic treatment (aPDT) using riboflavin for the treatment of BLB disease. Combining light and riboflavin (RF) therapy significantly reduced bacterial planktonic cells compared to RF alone. Photoactivated riboflavin also decreased biofilm biomass by reducing the number of viable sessile cells and the production of extracellular polymeric substances (EPS). Reactive oxygen species (ROS) levels in Xoo cells treated with photoactivated riboflavin were found to be significantly higher than in cells treated with riboflavin and light individually. Malondialdehyde (MDA) increased greatly in photoactivated riboflavin treated cells, indicating that severe oxidative damage was induced. Subsequently, a reduction in lactate dehydrogenase (LDH) activity in photoactivated riboflavin treated Xoo cells indicates that oxidative stress has disrupted the respiratory system, leading to bacterial cell death. In an ex vivo aPDT assay, photoactivated riboflavin successfully eradicated Xoo on the surface of rice leaves. Photoactivated riboflavin had no side effects on rice seed germination in subsequent trials, indicating that it is safe for agricultural applications. Therefore, all these findings suggest that aPDT is a potential alternative management strategy for BLB disease.

Photoinactivation of Yeast and Biofilm Communities of Candida albicans Mediated by ZnTnHex-2-PyP4+ Porphyrin

Candida albicans is the main cause of superficial candidiasis. While the antifungals available are defied by biofilm formation and resistance emergence, antimicrobial photodynamic inactivation (aPDI) arises as an alternative antifungal therapy. The tetracationic metalloporphyrin Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (ZnTnHex-2-PyP⁴⁺) has high photoefficiency and improved cellular interactions. We investigated the ZnTnHex-2-PyP⁴⁺ as a photosensitizer (PS) to photoinactivate yeasts and biofilms of C. albicans strains (ATCC 10231 and ATCC 90028) using a blue light-emitting diode. The photoinactivation of yeasts was evaluated by quantifying the colony forming units. The aPDI of ATCC 90028 biofilms was assessed by the MTT assay, propidium iodide (PI) labeling, and scanning electron microscopy. Mammalian cytotoxicity was investigated in Vero cells using MTT assay. The aPDI (4.3 J/cm²) promoted eradication of yeasts at 0.8 and 1.5 µM of PS for ATCC 10231 and ATCC 90028, respectively. At 0.8 µM and same light dose, aPDI-treated biofilms showed intense PI labeling, about 89% decrease in the cell viability, and structural alterations with reduced hyphae. No considerable toxicity was observed in mammalian cells. Our results introduce the ZnTnHex-2-PyP⁴⁺ as a promising PS to photoinactivate both yeasts and biofilms of C. albicans, stimulating studies with other Candida species and resistant isolates.

Evaluation of a Luminometric Cell Counting System in Context of Antimicrobial Photodynamic Inactivation

Antimicrobial resistance belongs to the most demanding medical challenges, and antimicrobial photodynamic inactivation (aPDI) is considered a promising alternative to classical antibiotics. However, the pharmacologic characterization of novel compounds suitable for aPDI is a tedious and time-consuming task that usually requires preparation of bacterial cultures and counting of bacterial colonies. In this study, we established and utilized a luminescence-based microbial cell viability assay to analyze the aPDI effects of two porphyrin-based photosensitizers (TMPyP and THPTS) on several bacterial strains with antimicrobial resistance. We demonstrate that after adaptation of the protocol and initial calibration to every specific bacterial strain and photosensitizer, the luminometric method can be used to reliably quantify aPDI effects in most of the analyzed bacterial strains. The interference of photosensitizers with the luminometric readout and the bioluminescence of some bacterial strains were identified as possible confounders. Using this method, we could confirm the susceptibility of several bacterial strains to photodynamic treatment, including extensively drug-resistant pathogens (XDR). In contrast to the conventional culture-based determination of bacterial density, the luminometric assay allowed for a much more time-effective analysis of various treatment conditions. We recommend this luminometric method for high-throughput tasks requiring measurements of bacterial viability in the context of photodynamic treatment approaches.

Metatranscriptomic Analyses Reveal the Functional Role of Botrytis cinerea in Biochemical and Textural Changes during Noble Rot of Grapevines

Botrytis cinerea, can lead to the formation of noble rot (NR) of grape berries under certain environmental conditions, resulting in favored metabolic and physical changes necessary for producing highly regarded botrytized wines. The functional genes involved in the textural and biochemical processes are still poorly characterized. We generated and analyzed metatranscriptomic data from healthy (H) berries and from berries representing the four stages of NR from the Tokaj wine region in Hungary over three months. A weighted gene co-expression network analysis (WGCNA) was conducted to link B. cinerea functional genes to grape berry physical parameters berry hardness (BH), berry skin break force (F_sk), berry skin elasticity (E_sk), and the skin break energy (W_sk). Clustered modules showed that genes involved in carbohydrate and protein metabolism were significantly enriched in NR, highlighting their importance in the grape berry structural integrity. Carbohydrate active enzymes were particularly up-regulated at the onset of NR (during the transition from phase I to II) suggesting that the major structural changes occur early in the NR process. In addition, we identified genes expressed throughout the NR process belonging to enriched pathways that allow B. cinerea to dominate and proliferate during this state, including sulphate metabolizing genes and genes involved in the synthesis of antimicrobials.

A nano phototheranostic approach of toluidine blue conjugated gold silver core shells mediated photodynamic therapy to treat diabetic foot ulcer

Diabetic foot infection caused by multidrug-resistant bacteria, is becoming serious problem. Moreover, polymicrobial biofilms contribute significantly to the persistent infections. In the present study, we investigated the effectiveness of novel toluidine blue conjugated chitosan coated gold-silver core-shell nanoparticles (TBO-chit-Au-AgNPs) mediated photodynamic therapy and demonstrate their use as a nontoxic antibacterial therapy to combat diabetic foot ulcer (DFU) caused by multi-drug resistant strains both in monomicrobial and polymicrobial state of infection. In vitro efficacy of TBO-chit-Au-AgNPs mediated photodynamic therapy (PDT) against polymicrobial biofilms was determined using standard plate count method and compared with that of monomicrobial biofilms of each species. Different anti-biofilm assays and microscopic studies were performed to check the efficacy of TBO-chit-Au-AgNPs mediated PDT, displayed significant decrease in the formation of biofilm. Finally, its therapeutic potential was validated in vivo type-2DFU. Cytokines level was found reduced, using nano-phototheranostic approach, indicating infection control. Expression profile of growth factors confirmed both the pathogenesis and healing of DFU. Hence, we conclude that TBO-chit-Au-AgNPs mediated PDT is a promising anti-bacterial therapeutic approach which leads to a synergistic healing of DFU caused by MDR bacterial strains.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

New Trends in Photodynamic Inactivation (PDI) Combating Biofilms in the Food Industry-A Review

Biofilms cause problems in the food industry due to their persistence and incompetent hygiene processing technologies. Interest in photodynamic inactivation (PDI) for combating biofilms has increased in recent years. This technique can induce microbial cell death, reduce cell attachment, ruin biofilm biomolecules and eradicate structured biofilms without inducing microbial resistance. This review addresses microbial challenges posed by biofilms in food environments and highlights the advantages of PDI in preventing and eradicating microbial biofilm communities. Current findings of the antibiofilm efficiencies of this technique are summarized. Additionally, emphasis is given to its potential mechanisms and factors capable of influencing biofilm communities, as well as promising hurdle strategies.

Photodynamic control of citrus crop diseases

Citrus are economically important fruit crops to which infectious diseases like citrus canker caused by Xanthomonas citri subs. citri, citrus variegated chlorosis caused by Xylella fastidiosa, "huanglongbing" associated with the presence of Candidatus liberibacter species, anthracnose caused by Colletotrichum gloeosporioides and citrus black spot caused by Phyllosticta citricarpa, impose significant losses. Control measures involve chemical treatment of orchards but often, eradication of infected plants is unavoidable. To circumvent the environmental impacts of pesticides and the socio-economic impacts of eradication, innovative antimicrobial approaches like photodynamic inactivation are being tested. There is evidence of the susceptibility of Xanthomonas citri subs. citri and C. gloeosporioides to photodynamic damage. However, the realistic assessment of perspectives for widespread application of photodynamic inactivation in the control of citrus diseases, necessarily implies that other microorganisms are also considered. This review intends to provide a critical summary of the current state of research on photodynamic inactivation of citrus pathogens and to identify some of the current limitations to the widespread use of photodynamic treatments in citrus crops.

Genetic Factors Affect the Survival and Behaviors of Selected Bacteria during Antimicrobial Blue Light Treatment

Antimicrobial resistance is a global, mounting and dynamic issue that poses an immediate threat to human, animal, and environmental health. Among the alternative antimicrobial treatments proposed to reduce the external use of antibiotics is electromagnetic radiation, such as blue light. The prevailing mechanistic model is that blue light can be absorbed by endogenous porphyrins within the bacterial cell, inducing the production of reactive oxygen species, which subsequently inflict oxidative damages upon different cellular components. Nevertheless, it is unclear whether other mechanisms are involved, particularly those that can affect the efficacy of antimicrobial blue light treatments. In this review, we summarize evidence of inherent factors that may confer protection to a selected group of bacteria against blue light-induced oxidative damages or modulate the physiological characteristics of the treated bacteria, such as virulence and motility. These include descriptions of three major photoreceptors in bacteria, chemoreceptors, SOS-dependent DNA repair and non-SOS protective mechanisms. Future directions are also provided to assist with research efforts to increase the efficacy of antimicrobial blue light and to minimize the development of blue light-tolerant phenotypes.

Antimicrobial photodynamic therapy (aPDT) for biofilm treatments. Possible synergy between aPDT and pulsed electric fields

Currently, microbial biofilms have been the cause of a wide variety of infections in the human body, reaching 80% of all bacterial and fungal infections. The biofilms present specific properties that increase the resistance to antimicrobial treatments. Thus, the development of new approaches is urgent, and antimicrobial photodynamic therapy (aPDT) has been shown as a promising candidate. aPDT involves a synergic association of a photosensitizer (PS), molecular oxygen and visible light, producing highly reactive oxygen species (ROS) that cause the oxidation of several cellular components. This therapy attacks many components of the biofilm, including proteins, lipids, and nucleic acids present within the biofilm matrix; causing inhibition even in the cells that are inside the extracellular polymeric substance (EPS). Recent advances in designing new PSs to increase the production of ROS and the combination of aPDT with other therapies, especially pulsed electric fields (PEF), have contributed to enhanced biofilm inhibition. The PEF has proven to have antimicrobial effect once it is known that extensive chemical reactions occur when electric fields are applied. This type of treatment kills microorganisms not only due to membrane rupture but also due to the formation of reactive compounds including free oxygen, hydrogen, hydroxyl and hydroperoxyl radicals. So, this review aims to show the progress of aPDT and PEF against the biofilms, suggesting that the association of both methods can potentiate their effects and overcome biofilm infections.

Photodynamic Inactivation of an Endodontic Bacteria Using Diode Laser and Indocyanine Green-Loaded Nanosphere

Apical periodontitis, an inflammatory lesion causing bone resorption around the apex of teeth, is treated by eradicating infectious bacteria from the root canal. However, it has a high recurrence rate and often requires retreatment. We investigated the bactericidal effect of antimicrobial photodynamic therapy (aPDT)/photodynamic antimicrobial chemotherapy (PACT) using indocyanine green (ICG)-loaded nanospheres coated with chitosan and a diode laser on a biofilm of Enterococcus faecalis, a pathogen of refractory apical periodontitis. Biofilm of E. faecalis was cultured in a porcine infected root canal model. ICG solution was injected into the root canal, which was then irradiated with a laser (810 nm wavelength) from outside the root canal. The bactericidal effect was evaluated by colony counts and scanning electron microscopy. The result of the colony counts showed a maximum 1.89 log reduction after irradiation at 2.1 W for 5 min. The temperature rise during aPDT/PACT was confirmed to be within a safe range. Furthermore, the light energy transmittance through the root was at a peak approximately 1 min after the start of irradiation, indicating that most of the ICG in the root canal was consumed. This study shows that aPDT/PACT can suppress E. faecalis in infected root canals with high efficiency.

Photoinactivation of Pseudomonas aeruginosa Biofilm by Dicationic Diaryl-Porphyrin

In recent years, antimicrobial photodynamic therapy (aPDT) has received increasing attention as a promising tool aimed at both treating microbial infections and sanitizing environments. Since biofilm formation on biological and inert surfaces makes difficult the eradication of bacterial communities, further studies are needed to investigate such tricky issue. In this work, a panel of 13 diaryl-porphyrins (neutral, mono- and di-cationic) was taken in consideration to photoinactivate Pseudomonas aeruginosa. Among cationic photosensitizers (PSs) able to efficiently bind cells, in this study two dicationic showed to be intrinsically toxic and were ruled out by further investigations. In particular, the dicationic porphyrin (P11) that was not toxic, showed a better photoinactivation rate than monocationic in suspended cells. Furthermore, it was very efficient in inhibiting the biofilms produced by the model microorganism Pseudomonas aeruginosa PAO1 and by clinical strains derived from urinary tract infection and cystic fibrosis patients. Since P. aeruginosa represents a target very difficult to inactivate, this study confirms the potential of dicationic diaryl-porphyrins as photo-activated antimicrobials in different applicative fields, from clinical to environmental ones.

Photodynamic Antimicrobial Chemotherapy: Advancements in Porphyrin-Based Photosensitize Development

The reduction of available drugs with effectiveness against microbes is worsening with the current global crisis of antimicrobial resistance. This calls for innovative strategies for combating antimicrobial resistance. Photodynamic Antimicrobial Chemotherapy (PACT) is a relatively new method that utilizes the combined action of light, oxygen, and a photosensitizer to bring about the destruction of microorganisms. This technique has been found to be effective against a wide spectrum of microorganisms, including bacteria, viruses, and fungi. Of greater interest is their ability to destroy resistant strains of microorganisms and in effect help in combating the emergence of antimicrobial resistance. This manuscript reviews porphyrins and porphyrin-type photosensitizers that have been studied in the recent past with a focus on their structure-activity relationship.

Reactive Oxygen Species in Pathogen Clearance: The Killing Mechanisms, the Adaption Response, and the Side Effects

Reactive oxygen species (ROS) are attractive weapons in both antibiotic-mediated killing and host-mediated killing. However, the involvement of ROS in antibiotic-mediated killing and complexities in host environments challenge the paradigm. In the case of bacterial pathogens, the examples of some certain pathogens thriving under ROS conditions prompt us to focus on the adaption mechanism that pathogens evolve to cope with ROS. Based on these, we here summarized the mechanisms of ROS-mediated killing of either antibiotics or the host, the examples of bacterial adaption that successful pathogens evolved to defend or thrive under ROS conditions, and the potential side effects of ROS in pathogen clearance. A brief section for new antibacterial strategies centered around ROS was also addressed.

Antimicrobial and antibiofilm photodynamic therapy against vancomycin resistant Staphylococcus aureus (VRSA) induced infection in vitro and in vivo

Biofilm mediated infection caused by multi-drug resistant bacteria are difficult to treat since it protects the microorganisms by host defense system, making them resistant to antibiotics and other antimicrobial agents. Combating such type of nosocomial infection, especially in immunocompromised patients, is an urgent need and foremost challenge faced by clinicians. Therefore, antimicrobial photodynamic therapy (aPDT) has been intensely pursued as an alternative therapy for bacterial infections. aPDT leads to the generation of reactive oxygen species (ROS) that destroy bacterial cells in the presence of a photosensitizer, visible light and oxygen. Here, we elucidated a possibility of its clinical application by reducing the treatment time and exposing curcumin to 20 J/cm² of blue laser light, which corresponds to only 52 s to counteract vancomycin resistant Staphylococcus aureus (VRSA) both in vitro and in vivo. To understand the mechanism of action, the generation of total reactive oxygen species (ROS) was quantified by 2'-7'-dichlorofluorescein diacetate (DCFH-DA) and the type of phototoxicity was confirmed by fluorescence spectroscopic analysis. The data showed more production of singlet oxygen, indicating type-II phototoxicity. Different anti-biofilm assays (crystal violet and congo red assays) and microscopic studies were performed at sub-MIC concentration of curcumin followed by treatment with laser light against preformed biofilm of VRSA. The result showed significant reduction in the preformed biofilm formation. Finally, its therapeutic potential was validated in skin abrasion wistar rat model. The result showed significant inhibition of bacterial growth. Furthermore, immunomodulatory analysis with rat serum was performed. A significant reduction in expression of proinflammatory cytokines TNF-α and IL-6 were observed. Hence, we conclude that curcumin mediated aPDT with 20 J/cm² of blue laser treatment (for 52 s) could be used against multi-drug resistant bacterial infections and preformed biofilm formation as a potential therapeutic approach.

Synthesis, theoretical calculations and laser flash photolysis studies of selected amphiphilic porphyrin derivatives used as biofilm photodegradative materials

Two positively charged metalloporphyrins were synthesized and theoretical studies were carried out. The complexes efficiently eradicated S. aureus and E. coli bacterial cells at 415 nm.

Antimicrobial Blue Light versus Pathogenic Bacteria: Mechanism, Application in the Food Industry, Hurdle Technologies and Potential Resistance

Blue light primarily exhibits antimicrobial activity through the activation of endogenous photosensitizers, which leads to the formation of reactive oxygen species that attack components of bacterial cells. Current data show that blue light is innocuous on the skin, but may inflict photo-damage to the eyes. Laboratory measurements indicate that antimicrobial blue light has minimal effects on the sensorial and nutritional properties of foods, although future research using human panels is required to ascertain these findings. Food properties also affect the efficacy of antimicrobial blue light, with attenuation or enhancement of the bactericidal activity observed in the presence of absorptive materials (for example, proteins on meats) or photosensitizers (for example, riboflavin in milk), respectively. Blue light can also be coupled with other treatments, such as polyphenols, essential oils and organic acids. While complete resistance to blue light has not been reported, isolated evidence suggests that bacterial tolerance to blue light may occur over time, especially through gene mutations, although at a slower rate than antibiotic resistance. Future studies can aim at characterizing the amount and type of intracellular photosensitizers across bacterial species and at assessing the oxygen-independent mechanism of blue light-for example, the inactivation of spoilage bacteria in vacuum-packed meats.

The effects of aloe emodin-mediated antimicrobial photodynamic therapy on drug-sensitive and resistant Candida albicans

The extensive and repetitive use of antifungal drugs has led to the development of drug-resistant Candida albicans. Antimicrobial photodynamic therapy (aPDT) has received considerable attention as an emerging and promising approach to combat drug-resistant microbes. This study evaluated the photodynamic effects mediated by aloe emodin (AE), a natural compound isolated from Aloe vera and Rheum palmatum, on azole-sensitive and azole-resistant C. albicans in vitro. AE exhibited no significant dark toxicity, but in the presence of light, effectively inactivated C. albicans cells in a concentration-dependent manner. The uptake of AE by fungal cells was investigated by confocal laser scanning microscopy (CLSM), and the results showed that AE possessed stronger ability to enter into C. albicans cells following light irradiation. Transmission electron microscopy analysis suggested that AE-mediated aPDT could induce damage to the cell wall, cytoplasm, and nucleus. Damage to the surface of C. albicans was observed by scanning electron microscopy. These results suggest that AE is a potential PS for use in aPDT of drug-resistant C. albicans strains, and AE-mediated aPDT shows promise as an antifungal treatment.

Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is an opportunistic human pathogen causing devastating acute and chronic infections in individuals with compromised immune systems. Its highly notorious persistence in clinical settings is attributed to its ability to form antibiotic-resistant biofilms. Biofilm is an architecture built mostly by autogenic extracellular polymeric substances which function as a scaffold to encase the bacteria together on surfaces, and to protect them from environmental stresses, impedes phagocytosis and thereby conferring the capacity for colonization and long-term persistence. Here we review the current knowledge on P. aeruginosa biofilms, its development stages, and molecular mechanisms of invasion and persistence conferred by biofilms. Explosive cell lysis within bacterial biofilm to produce essential communal materials, and interspecies biofilms of P. aeruginosa and commensal Streptococcus which impedes P. aeruginosa virulence and possibly improves disease conditions will also be discussed. Recent research on diagnostics of P. aeruginosa infections will be investigated. Finally, therapeutic strategies for the treatment of P. aeruginosa biofilms along with their advantages and limitations will be compiled.

Antimicrobial photodynamic treatment as an alternative approach for Alicyclobacillus acidoterrestris inactivation

Alicyclobacillus acidoterrestris is a cause of major concern for the orange juice industry due to its thermal and chemical resistance, as well as its spoilage potential. A. acidoterrestris spoilage of orange juice is due to off-flavor taints from guaiacol production and some halophenols. The present study aimed to evaluate the effectiveness of antimicrobial Photodynamic Treatment (aPDT) as an emerging technology to inactivate the spores of A. acidoterrestris. The aPDT efficiency towards A. acidoterrestris was evaluated using as photosensitizers the tetracationic porphyrin (Tetra-Py⁺-Me) and the phenothiazinium dye new methylene blue (NMB) in combination with white light-emitting diode (LED; 400-740 nm; 65-140 mW/cm²). The spores of A. acidoterrestris were cultured on YSG agar plates (pH 3.7 ± 0.1) at 45 °C for 28 days and submitted to the aPDT with Tetra-Py⁺-Me and NMB at 10 μM in phosphate-buffered saline (PBS) in combination with white light (140 mW/cm²). The use of Tetra-Py⁺-Me at 10 μM resulted in a 7.3 ± 0.04 log reduction of the viability of A. acidoterrestris spores. No reductions in the viability of this bacterium were observed with NMB at 10 μM. Then, the aPDT with Tetra-Py⁺-Me and NMB at 10 μM in orange juice (UHT; pH 3.9; 11°Brix) alone and combined with potassium iodide (KI) was evaluated. The presence of KI was able to potentiate the aPDT process in orange juice, promoting the inactivation of 5 log CFU/mL of A. acidoterrestris spores after 10 h of white light exposition (140 mW/cm²). However, in the absence of KI, both photosensitizers did not promote a significant reduction in the spore viability. The inactivation of A. acidoterrestris spores artificially inoculated in orange peels (10⁵ spores/mL) was also assessed using Tetra-Py⁺-Me at 10 and 50 μM in the presence and absence of KI in combination with white light (65 mW/cm²). No significant reductions were observed (p < .05) when Tetra-Py⁺-Me was used at 10 μM, however at the highest concentration (50 μM) a significant spore reduction (≈ 2.8 log CFU/mL reductions) in orange peels was observed after 6 h of sunlight exposition (65 mW/cm²). Although the color, total phenolic content (TPC), and antioxidant capacity of orange juice and peel (only color evaluation) seem to have been affected by light exposition, the impact on the visual and nutritional characteristics of the products remains inconclusive so far. Besides that, the results found suggest that aPDT can be a potential method for the reduction of A. acidoterrestris spores on orange groves.

Photodynamic inactivation of the phytopathogenic bacterium Xanthomonas citri subsp. citri

The present work intended to evaluate the applicability of photodynamic inactivation (PDI) of Xanthomonas citri subsp. citri with toluidine blue O (TBO), a commercial photosensitizer, as a strategy to control citrus canker. Assays were conducted with cell suspensions and biofilms, constructed either on polypropylene microtubes (in vitro assays) or on the surface of orange leaves (ex vivo assays), in the presence of TBO and under irradiation with artificial white light or natural sunlight. PDI assays using TBO alone caused a maximum 5·8 log10 reduction of X. citri viable cells in suspensions, and a much smaller inactivation (1·5 log10) in biofilms. However, concomitant use of KI potentiated the TBO photosensitization. Biofilms were inactivated down to the detection limit (>6 log10 reduction) with 5·0 µmol l^-1 TBO + 10 mmol l^-1 KI (in vitro) or 5·0 µmol l^-1 TBO + 100 mmol l^-1 KI (ex vivo) after artificial white light irradiation. Under natural sunlight, a reduction down to the detection limit of the Miles-Misra method was achieved with 50 µmol l^-1 TBO and 100 mmol l^-1 KI. PDI has potential to be applied in the control of citrus canker in field conditions although further studies are needed to show that there are no risks to plant physiology or fruit quality. SIGNIFICANCE AND IMPACT OF THE STUDY: Xanthomonas citri subsp. citri is a major cause of disease in citrus orchards. Because of the low efficacy and high environmental toxicity of copper-based treatments, there is growing interest on more sustainable phytosanitary approaches. Photodynamic inactivation (PDI) is being successfully used to control infectious agents and literature reports indicate that it is effective against some fungi and bacteria attacking fruit crops. The results of the present work open the perspective of using a low-cost photosensitizer and sunlight, as energy source, to control of the causative agent of citrus canker.

Photodynamic Inactivation of ESKAPE Group Bacterial Pathogens in Planktonic and Biofilm Cultures Using Metallated Porphyrin-Doped Conjugated Polymer Nanoparticles

Photodynamic inactivation (PDI) protocols using photoactive metallated porphyrin-doped conjugated polymer nanoparticles (CPNs) and blue light were developed to eliminate multidrug-resistant pathogens. CPNs-PDI protocols using varying particle concentrations and irradiation doses were tested against nine pathogenic bacterial strains including antibiotic-resistant bacteria of the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens group. The bactericidal effect was achieved in methicillin-resistant Staphylococus aureus (S. aureus) strains using low light doses (9.6-14.4 J/cm²), while Gram-negative bacteria required a higher light dose (28.8 J/cm²). The bacteria-CPN interaction was studied through flow cytometry, taking advantage of the intrinsic CPN fluorescence, demonstrating that CPNs efficiently bind to the bacterial envelope. Finally, the performance of CPNs-PDI was explored in biofilms; good antibiofilm ability and almost complete eradication were observed for S. aureus and Escherichia coli biofilms, respectively, using confocal microscopy. Overall, we demonstrated that CPNs-PDI is an efficient tool not only to kill superbugs as sessile cells but also to disrupt and eradicate biofilms of highly relevant pathogenic bacterial species.

Impact of Protoporphyrin Lysine Derivatives on the Ability of Nosema ceranae Spores to Infect Honeybees

Simple Summary

Honeybees, which are important for the development and maintenance of natural ecosystems, are infected by microsporidia, Nosema apis and N. ceranae. These parasites induce a disease named nosemosis contributing to the impairment of digestion and nutrient absorption, ultimately leading to total colony collapse. The need for research into the control of N. ceranae has become increasingly important. Promising compounds for the treatment of nosemosis are porphyrins. In the present study, we examined the effects of three different porphyrins on the infectivity of N. ceranae microsporidia. A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the control bees (infected with untreated spores). We showed that protoporphyrin lysine derivatives in particular prevented the development of Nosema spores and simultaneously extended bee life spans (up to 50%). The results also indicate that these porphyrins may contribute to the reduction in digestive nutrient absorption disorders in bees. The present findings can be used to develop a new class of drugs for combating nosemosis. These compounds may serve as preventive or disinfection agents through direct inactivation of Nosema both in the midgut and outside the host body, i.e., in the hive.

Abstract

The effect of two protoporphyrin IX derivatives conjugated with single (PP[Lys(TFA)-OH)]₂) or double (PP[Lys(TFA)-Lys(TFA)-OH]₂) lysine moieties on the infectious capacity of Nosema ceranae spores was examined, and their efficacies were compared with those of a cationic porphyrin (H₂TTMePP). Honeybees were inoculated with spores preincubated with porphyrins or with untreated spores (control). A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the infected control. Porphyrins 1 and 2 reduced the infectious capability of microsporidia more efficiently than porphyrin 3, with bee mortality declining to almost 50%. Confocal analysis of the midguts of infected bees revealed distinct differences in the number of spores between the control group and the group infected with PP[Lys(TFA)-Lys(TFA)-OH]₂-treated spores. Notably, bees with a reduced level of infection consumed less sucrose syrup than the control bees, indicating a reduction in digestive disorders and an improvement in food absorption.

Antimicrobial Photodynamic Therapy with Chlorin e6 Is Bactericidal against Biofilms of the Primary Human Otopathogens

Otitis media (OM), or middle ear disease, is the most prevalent bacterial infection in children and the primary reason for antibiotic use and surgical intervention in the pediatric population. Biofilm formation by the major bacterial otopathogens, Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae, has been shown to occur within the middle ears of OM patients and is a key factor in the development of recurrent disease, which may result in hearing impairment and developmental delays. Bacterial biofilms are inherently impervious to most antibiotics and present a significant challenge to the immune system. In this study, we demonstrate that antimicrobial photodynamic therapy (aPDT) using the photosensitizer chlorin e6 elicits significant bactericidal activity versus planktonic and biofilm-associated otopathogens and supports further analyses of this novel, efficacious, and promising technology as an adjunctive treatment for acute and recurrent OM.

Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae (NTHi) are ubiquitous upper respiratory opportunistic pathogens. Together, these three microbes are the most common causative bacterial agents of pediatric otitis media (OM) and have therefore been characterized as the primary human otopathogens. OM is the most prevalent bacterial infection in children and the primary reason for antibiotic administration in this population. Moreover, biofilm formation has been confirmed as a primary mechanism of chronic and recurrent OM disease. As bacterial biofilms are inherently metabolically recalcitrant to most antibiotics and these complex structures also present a significant challenge to the immune system, there is a clear need to identify novel antimicrobial approaches to treat OM infections. In this study, we evaluated the potential efficacy of antibacterial photodynamic therapy (aPDT) with the photosensitizer chlorin e6 (Ce6) against planktonic as well as biofilm-associated M. catarrhalis, S. pneumoniae, and NTHi. Our data indicate aPDT with Ce6 elicits significant bactericidal activity against both planktonic cultures and established biofilms formed by the three major otopathogens (with an efficacy of ≥99.9% loss of viability). Notably, the implementation of a novel, dual-treatment aPDT protocol resulted in this disinfectant effect on biofilm-associated bacteria and, importantly, inhibited bacterial regrowth 24 h posttreatment. Taken together, these data suggest this novel Ce6-aPDT treatment may be a powerful and innovative therapeutic strategy to effectively treat and eradicate bacterial OM infections and, significantly, prevent the development of recurrent disease.

IMPORTANCE Otitis media (OM), or middle ear disease, is the most prevalent bacterial infection in children and the primary reason for antibiotic use and surgical intervention in the pediatric population. Biofilm formation by the major bacterial otopathogens, Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae, has been shown to occur within the middle ears of OM patients and is a key factor in the development of recurrent disease, which may result in hearing impairment and developmental delays. Bacterial biofilms are inherently impervious to most antibiotics and present a significant challenge to the immune system. In this study, we demonstrate that antimicrobial photodynamic therapy (aPDT) using the photosensitizer chlorin e6 elicits significant bactericidal activity versus planktonic and biofilm-associated otopathogens and supports further analyses of this novel, efficacious, and promising technology as an adjunctive treatment for acute and recurrent OM.

Bioactivity studies of porphyrinoids against microsporidia isolated from honeybees

Microsporidian infections are dangerous to honeybees due to the absence of an efficient treatment for nosemosis. In the present work, the abilities of several porphyrins to directly inactivate microsporidia derived from Nosema-infected honeybees were studied in vitro. Amide derivatives of protoporphyrin IX (PPIX) conjugated with one and two amino acid moieties were synthesized, and their activities were compared with those of two cationic porphyrins, TMePyP and TTMePP. The most active porphyrins, PP[Lys-Asp]₂, PP[Lys-TFA]₂, PP[Asp(ONa)₂]₂ and PP[Lys-Lys]₂ at concentrations as low as 10–50 µM exerted significant effects on microsporidia, reducing the number of spores by 67–80% compared to the control. Live-cell imaging of the spores treated with porphyrins showed that only 1.6% and 3.0% of spores remained alive after 24 h-incubation with 50 µM PP[Asp(ONa)₂]₂ and PP[Lys-Asp]₂, respectively. The length of the amino acid side chains and their identity in the PPIX molecules affected the bioactivity of the porphyrin. Importantly, the irradiation of the porphyrins did not enhance their potency in destroying Nosema spores. We showed that the porphyrins accumulated inside the living spores but not inside dead spores, thus the destruction of the microsporidia by non-metallated porphyrins is not dependent on photosensitization, but is associated with their active transport into the spore cell. When administered to honeybees in vivo, PPIX[Lys-TFA]₂ and PPIX[Lys-Lys]₂ reduced spore loads by 69–76% in infected individuals. They both had no toxic effect on honeybees, in contrast to zinc-coordinated porphyrin.

Innovative Strategies Toward the Disassembly of the EPS Matrix in Bacterial Biofilms

Bacterial biofilms represent a major concern at a worldwide level due to the high demand for implantable medical devices and the rising numbers of bacterial resistance. The complex structure of the extracellular polymeric substances (EPS) matrix plays a major role in this phenomenon, since it protects bacteria from antibiotics, avoiding drug penetration at bactericidal concentrations. Besides, this structure promotes bacterial cells to adopt a dormant lifestyle, becoming less susceptible to antibacterial agents. Currently, the available treatment for biofilm-related infections consists in the administration of conventional antibiotics at high doses for a long-term period. However, this treatment lacks efficiency against mature biofilms and for implant-associated biofilms it may be necessary to remove the medical device. Thus, biofilm-related infections represent an economical burden for the healthcare systems. New strategies focusing on the matrix are being highlighted as alternative therapies to eradicate biofilms. Here, we outline reported matrix disruptive agents, nanocarriers, and technologies, such as application of magnetic fields, photodynamic therapy, and ultrasounds, that have been under investigation to disrupt the EPS matrix of clinically relevant bacterial biofilms. In an ideal therapy, a synergistic effect between antibiotics and the explored innovated strategies is aimed to completely eradicate biofilms and avoid antimicrobial resistance phenomena.