The effectiveness of photodynamic therapy on planktonic cells and biofilms and its role in wound healing

The effect of low-dose photodynamic therapy using the photosensitizer chloroaluminum phthalocyanine on a scratch wound model in skin fibroblasts

Different approaches on wound healing have been developed over the years but they suffer from high costs and adverse effects for the patients. The current paper was designed to study low dose PDT, a novel healing approach, in an in vitro fibroblasts wound healing model. Chloroaluminum phthalocyanine (AlClPc) was used as photosensitizer and was activated by a red diode laser at 661 nm. After PDT optimization, wound closure rate and reactive oxygen species were quantified by image processing and analysis. Our results revealed that wound healing rates were significantly higher in PDT treated groups than in the control. Additionally, the study revealed that a prolonged ROS increase did not promote wound closure, while a small increase acted as a trigger, resulting in faster wound closure. Concluding, low dose PDT using AlClPc enhances wound healing in vitro in a ROS dependent manner, allowing the assumption of similar positive effects in vivo.

Clostridioides difficile Biofilm

Clostridioides difficile infection (CDI), previously Clostridium difficile infection, is a symptomatic infection of the large intestine caused by the spore-forming anaerobic, gram-positive bacterium Clostridioides difficile. CDI is an important healthcare-associated disease worldwide, characterized by high levels of recurrence, morbidity, and mortality. CDI is observed at a higher rate in immunocompromised patients after antimicrobial therapy, with antibiotics disrupting the commensal microbiota and promoting C. difficile colonization of the gastrointestinal tract.A rise in clinical isolates resistant to multiple antibiotics and the reduced susceptibility to the most commonly used antibiotic molecules have made the treatment of CDI more complicated, allowing the persistence of C. difficile in the intestinal environment.Gut colonization and biofilm formation have been suggested to contribute to the pathogenesis and persistence of C. difficile. In fact, biofilm growth is considered as a serious threat because of the related antimicrobial tolerance that makes antibiotic therapy often ineffective. This is the reason why the involvement of C. difficile biofilm in the pathogenesis and recurrence of CDI is attracting more and more interest, and the mechanisms underlying biofilm formation of C. difficile as well as the role of biofilm in CDI are increasingly being studied by researchers in the field.Findings on C. difficile biofilm, possible implications in CDI pathogenesis and treatment, efficacy of currently available antibiotics in treating biofilm-forming C. difficile strains, and some antimicrobial alternatives under investigation will be discussed here.

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

The photosensitizer-based therapies enhance the repairing of skin wounds

Wound repair remains a clinical challenge and bacterial infection is a common complication that may significantly delay healing. Therefore, proper and effective wound management is essential. The photosensitizer-based therapies mainly stimulate the photosensitizer to generate reactive oxygen species through appropriate excitation source irradiation, thereby killing pathogenic microorganisms. Moreover, they initiate local immune responses by inducing the recruitment of immune cells as well as the production of proinflammatory cytokines. In addition, these therapies can stimulate the proliferation, migration and differentiation of skin resident cells, and improve the deposition of extracellular matrix; subsequently, they promote the re-epithelialization, angiogenesis, and tissue remodeling. Studies in multiple animal models and human skin wounds have proved that the superior sterilization property and biological effects of photosensitizer-based therapies during different stages of wound repair. In this review, we summarize the recent advances in photosensitizer-based therapies for enhancing tissue regeneration, and suggest more effective therapeutics for patients with skin wounds.

Promising Photocytotoxicity of Water-Soluble Phtalocyanine against Planktonic and Biofilm Pseudomonas aeruginosa Isolates from Lower Respiratory Tract and Chronic Wounds

Alternative methods of killing microbes have been extensively researched in connection with the widespread appearance of antibiotic resistance among pathogenic bacteria. In this study, we report on in vitro antimicrobial phototoxicity research of cationic phthalocyanine with 2-(4-N-methylmorpholin-4-ium-4-yl)ethoxy substituents against selected clinical strains of Pseudomonas aeruginosa isolated from the lower respiratory tract and chronic wounds. The microorganisms tested in the research were analyzed in terms of drug resistance and biofilm formation. The photocytotoxic effect of phthalocyanine was determined by the reduction factor of bacteria. The studied cationic phthalocyanine at a concentration of 1.0 × 10−4 M, when activated by light, revealed a significant reduction factor, ranging from nearly 4 to 6 log, of P. aeruginosa cells when compared to the untreated control group. After single irradiation, a decrease in the number of bacteria in biofilm ranging from 1.3 to 4.2 log was observed, whereas the second treatment significantly improved the bacterial reduction factor from 3.4 to 5.5 log. It is worth mentioning that a boosted cell-death response was observed after the third irradiation, with a bacterial reduction factor ranging from 4.6 to 6.4 log. According to the obtained results, the tested photosensitizer can be considered as a potential antimicrobial photodynamic therapy against multidrug-resistant P. aeruginosa.

Understanding How Staphylococcal Autolysin Domains Interact With Polystyrene Surfaces

Biofilms, when formed on medical devices, can cause malfunctions and reduce the efficiency of these devices, thus complicating treatments and serving as a source of infection. The autolysin protein of Staphylococcus epidermidis contributes to its biofilm forming ability, especially on polystyrene surfaces. R2ab and amidase are autolysin protein domains thought to have high affinity to polystyrene surfaces, and they are involved in initial bacterial attachment in S. epidermidis biofilm formation. However, the structural details of R2ab and amidase binding to surfaces are poorly understood. In this study, we have investigated how R2ab and amidase influence biofilm formation on polystyrene surfaces. We have also studied how these proteins interact with polystyrene nanoparticles (PSNPs) using biophysical techniques. Pretreating polystyrene plates with R2ab and amidase domains inhibits biofilm growth relative to a control protein, indicating that these domains bind tightly to polystyrene surfaces and can block bacterial attachment. Correspondingly, we find that both domains interact strongly with anionic, carboxylate-functionalized as well as neutral, non-functionalized PSNPs, suggesting a similar binding interaction for nanoparticles and macroscopic surfaces. Both anionic and neutral PSNPs induce changes to the secondary structure of both R2ab and amidase as monitored by circular dichroism (CD) spectroscopy. These changes are very similar, though not identical, for both types of PSNPs, suggesting that carboxylate functionalization is only a small perturbation for R2ab and amidase binding. This structural change is also seen in limited proteolysis experiments, which exhibit substantial differences for both proteins when in the presence of carboxylate PSNPs. Overall, our results demonstrate that the R2ab and amidase domains strongly favor adsorption to polystyrene surfaces, and that surface adsorption destabilizes the secondary structure of these domains. Bacterial attachment to polystyrene surfaces during the initial phases of biofilm formation, therefore, may be mediated by aromatic residues, since these residues are known to drive adsorption to PSNPs. Together, these experiments can be used to develop new strategies for biofilm eradication, ensuring the proper long-lived functioning of medical devices.

Effect of Different Irradiation Modes of Azulene-mediated Photodynamic Therapy on Singlet Oxygen and PGE2 Formation

Azulene samples in ethanol/distilled water (1, 10 and 100 µm) were irradiated with a 638 nm red laser (0.5 watts, light-to-target distance 2 cm, energy density 4 or 40 J cm^-2 ) by either continuous, fractionation or pulse mode. Singlet oxygen in the samples was measured using 10 µm 9,10-dimethyl anthracene (positive control 10 μm erythrosine) and relative fluorescence intensities were measured at 375/436 nm excitation/emission. Peripheral blood mononuclear cells (PBMCs, 1 × 10⁵ cells/well) preincubated with 0.01 μg mL^-1 rhTNF-α for 6 h were cultured with irradiated azulene samples in RPMI-1640 under standard conditions. PGE₂ was quantified by rhPGE₂ ELISA kit using a Varioscan® microplate reader at an excitation wavelength of 420 nm. Kruskal Wallis with Dunn`s test was performed at a significance level of P < 0.05. The highest singlet oxygen amount was found in 10 µm azulene samples irradiated at 40 J cm^-2 under continuous mode (P = 0.001 when compared with 10 µm erythrosine). PGE₂ expression in rhTNF-α-induced PBMCs was reduced to 45% of control by 1 µm azulene irradiated at 40 J cm^-2 under fractionation mode. Fractionation mode with intermediate laser energy density in the presence of low concentration of azulene could increase singlet oxygen and tend to reduce PGE₂ .

Efficacy of the combination of minimally invasive CO2 laser incision with photodynamic therapy for infected epidermoid cysts

BACKGROUND

There are three main techniques for the removal of epidermoid cysts: traditional wide excision, minimal excision, and punch biopsy excision. For inflamed cysts, the wall is more friable and, therefore, more difficult to remove completely. The classic surgical excision always leads to a long scar or high rate of recurrence. CO₂ laser has been proven to result in minimal incision, less bleeding, no suture, and a smaller or no scar. Photodynamic therapy (PDT) has been proposed as an antimicrobial alternative for common and drug-resistant bacteria in nonspecific and multiple sites. It was also shown to be effective in accelerating healing and inhibiting excessive proliferation of hyperplastic scar. Thus, we combined minimally invasive CO₂ laser incision with PDT for epidermoid cysts with infection.

METHODS

Thirty-three patients had a total of 39 infectious cysts. Two of the patients withdrew due to the high cost after 1 treatment session. After local injection of anesthesia, a hole measuring 2-3 mm was made at the pore in the upper part of the cyst along skin texture by CO₂ laser (power 5 W, surgical pattern). The contents of the cyst were extracted through the hole using a curette and compression with gauze. PDT was then performed immediately. A total of 3 PDT sessions were recommended. The overall clinical effects, recurrence rates, cosmetic outcomes, adverse events, and patient satisfaction were assessed.

RESULTS

We achieved a 97% success rate in 31 patients with 34 lesions using a combination of minimally invasive CO₂ laser incision with PDT. At the 6- to 12-month follow-up, 30 of the patients had excellent cosmetic outcomes and satisfactory therapeutic effect. Pain during the illumination process, which can be relieved by dynamic cold air, was the primary adverse event.

CONCLUSION

Our results demonstrate promise for the combination of minimally invasive CO₂ laser incision with PDT as a safe and effective therapy for epidermoid cysts with infection. This treatment can inactivate a wide range of microbes including gram-positive and -negative bacteria, without developing drug resistance. Furthermore, it can promote fast wound healing and reduce scar formation.

Photodynamic therapy in infected venous and mixed leg ulcers: a pilot experience

OBJECTIVE

To assess the tolerability and efficacy of photodynamic therapy (PDT) with RLP068, a novel phthalocyanine-derived photosensitiser, in controlling the bacterial load in different leg ulcers, due to vascular pathophysiology.

METHOD

An observational study of patients with infected leg ulcers of different pathophysiology, admitted to the hospital for a skin grafting procedure, were included. All patients underwent two sessions of PDT at time zero and after 72 hours. A semi-quantitative swab was taken before and 30 minutes after both sessions of PTD. During the time interval between the two treatments the ulcer was covered with foam dressing and compression therapy was applied to all patients. No systemic or topical antibiotics were administered. Statistical analysis of results was performed.

RESULTS

A total of 36 patients (13 males, 23 females; aged 72.4±8.6 years, range: 55-85 years) were recruited; two had ulcers on both legs. PDT was shown to be effective in reducing bacterial load after the first treatment. Before the second PDT treatment (72 hours after first PDT treatment), a slight increase of the bacterial load was observed in all ulcers. However, after the second PDT session, bacterial swab results were negative in all but two ulcers. The procedure was well tolerated in all but four patients, who reported a very severe pain at baseline, which increased during treatment.

CONCLUSION

In this study, PDT was effective in reducing bacterial load in patients with infected vascular leg ulcers, and allowed successful skin grafting to take place in all patients. The treatment was generally well tolerated. Studies with a greater number of patients and a control group are planned to confirm these results.

Novel Polycationic Photosensitizers for Antibacterial Photodynamic Therapy

Antibacterial photodynamic therapy (APDT) is a promising method of treating local infected foci, in particular, surgical and burn wounds, trophic and diabetic ulcers. Photodynamic inactivation (PDI) is able to effectively destroy bacterial cells without them developing resistance in response to treatment.This work was dedicated to the study of photophysical and antibacterial properties of new photosensitizers (PS) based on polycationic phthalocyanines and synthetic bacteriochlorins for photodynamic inactivation of P. aeruginosa bacteria and their biofilms. Gram-negative bacteria P. aeruginosa are often found in infected wounds, presumably in biofilm state and are characterized by rather low susceptibility to APDT, which is a problem. PS were studied for possible aggregation at various concentrations by means of absorption and fluorescence spectroscopy. The results of studies of the ZnPcChol₈, (3-PyHp)₄BCBr₄ and (3-PyEBr)₄BCBr₄ in water and serum confirm the assumption of a low degree of their aggregation at high concentrations.Consequently, their photodynamic efficiency is high enabling to use these PS at high concentrations to sensitize pathological foci for APDT.It was shown that all the investigated PS had a high efficiency of photodynamic inactivation of Gram-negative bacteria P. aeruginosa, as well as their biofilms. Tetracationic hydrophilic near-infrared photosensitizer (3-PyEBr)₄BCBr₄ with reduced molecule size had significantly higher efficacy of photodynamic inactivation of P. aeruginosa biofilms compared with other studied photosensitizers.

Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action

Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC₅₀) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.

Antimicrobial photodynamic therapy-a promising treatment for prosthetic joint infections

Periprosthetic joint infection (PJI) is associated with high patient morbidity and a large financial cost. This study investigated Photodynamic Therapy (PDT) as a means of eradicating bacteria that cause PJI, using a laser with a 665-nm wavelength and methylene blue (MB) as the photosensitizer. The effectiveness of MB concentration on the growth inhibition of methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa and Acinetobacter baumannii was investigated. The effect of laser dose was also investigated and the optimized PDT method was used to investigate its bactericidal effect on species within planktonic culture and following the formation of a biofilm on polished titanium and hydroxyapatite coated titanium discs. Results showed that Staphylococci were eradicated at the lowest concentration of 0.1 mM methylene blue (MB). With P. aeruginosa and A. baumannii, increasing the MB concentration improved the bactericidal effect. When the laser dose was increased, results showed that the higher the power of the laser the more bacteria were eradicated with a laser power ≥ 35 J/cm² and an irradiance of 35 mW/cm², eradicating all S. epidermidis. The optimized PDT method had a significant bactericidal effect against planktonic MRSA and S. epidermidis compared to MB alone, laser alone, or control (no treatment). When biofilms were formed, PDT treatment had a significantly higher bactericidal effect than MB alone and laser alone for all species of bacteria investigated on the polished disc surfaces. P. aeruginosa grown in a biofilm was shown to be less sensitive to PDT when compared to Staphylococci, and a HA-coated surface reduced the effectiveness of PDT. This study demonstrated that PDT is effective for killing bacteria that cause PJI.

Extracellular Bacterial Proteases in Chronic Wounds: A Potential Therapeutic Target?

Significance: Bacterial biofilms are considered to be responsible for over 80% of persistent infections, including chronic lung infections, osteomyelitis, periodontitis, endocarditis, and chronic wounds. Over 60% of chronic wounds are colonized with bacteria that reside within a biofilm. The exaggerated proteolytic environment of chronic wounds, more specifically elevated matrix metalloproteinases, is thought to be one of the possible reasons as to why chronic wounds fail to heal. However, the role of bacterial proteases within chronic wounds is not fully understood. Recent Advances: Recent research has shown that bacterial proteases can enable colonization and facilitate bacterial immune evasion. The inhibition of bacterial proteases such as Pseudomonas aeruginosa elastase B (LasB) has resulted in the disruption of the bacterial biofilm in vitro. P. aeruginosa is thought to be a key pathogen in chronic wound infection, and therefore, the disruption of these biofilms, potentially through the targeting of P. aeruginosa bacterial proteases, is an attractive therapeutic endeavor. Critical Issues: Disrupting biofilm formation through the inhibition of bacterial proteases may lead to the dissemination of bacteria from the biofilm, allowing planktonic cells to colonize new sites within the wound. Future Directions: Despite a plethora of evidence supporting the role of bacterial proteases as virulence factors in infection, there remains a distinct lack of research into the effect of bacterial proteases in chronic wounds. To assess the viability of targeting bacterial proteases, future research should aim to understand the role of these proteases in a variety of chronic wound subtypes.

Modulation of virulence in Acinetobacter baumannii cells surviving photodynamic treatment with toluidine blue

INTRODUCTION

Widespread resistance to antimicrobial agents has led to a dearth of therapeutic choices in treating Acinetobacter baumannii infections, leading to new strategies for treatment being needed. We evaluated the effects of photodynamic therapy (PDT) as an alternative antimicrobial modality on the virulence features of cell-surviving PDT.

MATERIALS AND METHODS

To determine the sublethal PDT (sPDT), a colistin-resistant, extensively drug-resistant A. baumannii (CR-XDR-AB) clinical isolate and A. baumannii and ATCC 19606 strains, photosensitized with toluidine blue O (TBO), were irradiated with light emitting diodes, following bacterial viability measurements. The biofilm formation ability, outer membrane (OM) integrity, and antimicrobial susceptibility profiles were assessed for cell-surviving PDT. The effects of sPDT on the expression of virulent genes were evaluated by real-time quantitative reverse transcription PCR (qRT-PCR).

RESULTS

sPDT resulted in the reduction of the biofilm formation capacity, and its metabolic activity in strains. The OM permeability and efflux pump inhibition of the sPDT-treated CR-XDR-AB cells were increased; however, there was no significant change in OM integrity in ATCC 19606 strain after sPDT. sPDT reduced the minimum inhibitory concentrations of the most tested antimicrobials by ≥2-fold in CR-XDR-AB. lpsB, blsA, and dnaK were upregulated after the strains were treated with sPDT; however, a reduction in the expression of csuE, epsA, and abaI was observed in the treated strains after sPDT.

CONCLUSION

The susceptibility of CR-XDR-AB to a range of antibiotics was enhanced following sPDT. The virulence of strains is reduced in cells surviving PDT with TBO, and this may have potential implications of PDT for the treatment of A. baumannii infections.

Healthcare-associated infections, medical devices and biofilms: risk, tolerance and control

Biofilms are of great importance in infection control and healthcare-associated infections owing to their inherent tolerance and 'resistance' to antimicrobial therapies. Biofilms have been shown to develop on medical device surfaces, and dispersal of single and clustered cells implies a significant risk of microbial dissemination within the host and increased risk of infection. Although routine microbiological testing assists with the diagnosis of a clinical infection, there is no 'gold standard' available to reveal the presence of microbial biofilm from samples collected within clinical settings. Furthermore, such limiting factors as viable but non-culturable micro-organisms and small-colony variants often prevent successful detection. In order to increase the chances of detection and provide a more accurate diagnosis, a combination of microbiological culture techniques and molecular methods should be employed. Measures such as antimicrobial coating and surface alterations of medical devices provide promising opportunities in the prevention of biofilm formation on medical devices.