Development of Photodynamic Antimicrobial Chemotherapy (PACT) for Clostridium difficile

5-aminolevulinic acid photodynamic therapy for chronic wound infection in rats with diabetes

Recent research indicated that ulcers and peripheral vascular disease resulting from drug-resistant bacterial infections are the main causes of delayed healing in chronic diabetic wounds. 5-Aminolevulinic acid (ALA) is a second-generation endogenous photosensitizer. The therapeutic effect and mechanism of ALA-mediated photodynamic therapy (ALA-PDT) on methicillin-resistant Staphylococcus aureus (MRSA)-infected wounds in diabetic rats were investigated in this study. The results revealed the promising antibacterial effects of ALA-PDT MRSA in vitro, with a minimum inhibitory concentration and minimum bactericidal concentration of 250 and 500 μM, respectively. ALA-PDT also changed the permeability and structural integrity of bacterial cell membranes by producing reactive oxygen species. Meanwhile, ALA-PDT accelerated wound healing in MRSA-infected diabetic rats, with 5 % ALA-PDT achieving complete sterilization in 14 days and wound closure in 21 days. Treatment with 5 % ALA-PDT additionally improved the histopathological appearance of skin tissue, as well as fibrosis, inflammatory cytokine release, and angiogenesis-related protein expression. These findings indicated that ALA-PDT significantly promoted the healing of MRSA-infected wounds in diabetic rats by eliminating bacteria, inhibiting inflammation, generating granulation tissues, promoting neovascularization, and restoring damaged nerves. In addition, the healing mechanism was related to the activation of inflammatory and angiogenesis pathways through the regulation of tumor necrosis factor-alpha and interleukin-6 expression and upregulation of CD206, CD31, and VEGF. These findings underscored the potential role of ALA-PDT in promoting the healing of chronic diabetic wounds.

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.

The role of the light source in antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (APDT) is a promising approach to fight the growing problem of antimicrobial resistance that threatens health care, food security and agriculture. APDT uses light to excite a light-activated chemical (photosensitiser), leading to the generation of reactive oxygen species (ROS). Many APDT studies confirm its efficacy in vitro and in vivo against bacteria, fungi, viruses and parasites. However, the development of the field is focused on exploring potential targets and developing new photosensitisers. The role of light, a crucial element for ROS production, has been neglected. What are the main parameters essential for effective photosensitiser activation? Does an optimal light radiant exposure exist? And finally, which light source is best? Many reports have described the promising antibacterial effects of APDT in vitro, however, its application in vivo, especially in clinical settings remains very limited. The restricted availability may partially be due to a lack of standard conditions or protocols, arising from the diversity of selected photosensitising agents (PS), variable testing conditions including light sources used for PS activation and methods of measuring anti-bacterial activity and their effectiveness in treating bacterial infections. We thus sought to systematically review and examine the evidence from existing studies on APDT associated with the light source used. We show how the reduction of pathogens depends on the light source applied, radiant exposure and irradiance of light used, and type of pathogen, and so critically appraise the current state of development of APDT and areas to be addressed in future studies. We anticipate that further standardisation of the experimental conditions will help the field advance, and suggest key optical and biological parameters that should be reported in all APDT studies. More in vivo and clinical studies are needed and are expected to be facilitated by advances in light sources, leading to APDT becoming a sustainable, alternative therapeutic option for bacterial and other microbial infections in the future.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

Efficacy of Photodynamic Anti-Microbial Chemotherapy for Acanthamoeba Keratitis In Vivo

BACKGROUND AND OBJECTIVES

Acanthamoeba keratitis is a sight-threatening infectious disease that is difficult to treat. The aim of this study was to evaluate TONS504 (cationic chlorin derivative photosensitizer)-mediated photodynamic antimicrobial chemotherapy (PACT) in vivo as a potential treatment for Acanthamoeba keratitis.

STUDY DESIGN/MATERIALS AND METHODS

Acanthamoeba keratitis was induced by soft contact lenses incubated with 1 × 10⁵ /ml Acanthamoeba castellanii, which were placed over debrided corneas with temporary tarsorrhaphy. Thirty-eight male Japanese white rabbits were randomly divided into three groups (normal eye, no treatment, and treatment groups). TONS504 was administered as eye drops at 1 mg/ml, followed by light-emitting diode irradiation after the establishment of keratitis at 7 days after infectious contact lens exposure. All animals were evaluated under a slit-lamp microscope every 3 days for 6 days after the treatment. Clinical scores based on corneal epithelial defects detected by fluorescein staining, stromal opacity edema, and vascular infiltration into the cornea were determined. After 6 days, the eyes were enucleated for histopathological analysis.

RESULTS

Clinical signs of infection in the treatment group were markedly reduced for up to 6 days after treatment. Histopathology showed a regular arrangement of stromal fibers and a small number of inflammatory cells in 58% of the corneas. However, 42% of corneas in the treatment group showed infiltrating neutrophils and irregular alignment of stromal collagen fibers.

CONCLUSIONS

Our TONS504-PACT achieved complete recovery from keratitis in 58% of the rabbit models. Further studies are required to determine the conditions for the maximal effectiveness of our TONS504-PACT for Acanthamoeba keratitis. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Polyhedral Oligomeric Silsesquioxane (POSS)-Based Cationic Conjugated Oligoelectrolyte/Porphyrin for Efficient Energy Transfer and Multiamplified Antimicrobial Activity

Cationic quaternary ammonium (QA) groups and reactive oxygen species as two main approaches for antibacterial study have been intensively studied. Herein, we report a multifunctional antimicrobial agent (porphyrin-POSS-OPVE, PPO), which combines bacterial membrane intercalation, high density of local QA groups, efficient energy transfer, significantly reduced aggregation, and high water solubility into one single molecule. The light-harvesting PPO contains multiple donor-absorbing arms (oligo( p-phenylenevinylene) electrolytes, OPVEs) on its globular periphery and a central porphyrin acceptor in the core by using three-dimensional nanocages (polyhedral oligomeric silsesquioxanes, POSSs) as bridges. The antiaggregation ability of POSS and the highly efficient energy transfer from multiple OPVE arms to porphyrin could greatly amplify singlet oxygen generation in PPO. Particularly, OPVEs with QA terminal chains were able to intercalate into Escherichia coli membranes, which facilitated ¹O₂ diffusion and bacterial cell membrane disintegration by QA groups. The increased local cationic QA charges in OPVE arms can also enhance the biocidal activity of PPO. Benefiting from these satisfactory features, PPO exhibits multiamplified antibacterial efficacy under a very low concentration level and white light dose (400-700 nm, 6 mW·cm^-2, 5 min, 1.8 J·cm^-2) to Escherichia coli (8 μM) and Staphylococcus aureus (500 nM). Therefore, PPO shows great potential for photodynamic antimicrobial chemotherapy at a much lower irradiation light dose and photosensitizer concentration level compared to previous reports.

Combined Antimicrobial Activity of Photodynamic Inactivation and Antimicrobials-State of the Art

Antimicrobial photodynamic inactivation (aPDI) is a promising tool for the eradication of life-threatening pathogens with different profiles of resistance. This study presents the state-of-the-art published studies that have been dedicated to analyzing the bactericidal effects of combining aPDI and routinely applied antibiotics in in vitro (using biofilm and planktonic cultures) and in vivo experiments. Furthermore, the current paper reviews the methodology used to obtain the published data that describes the synergy between these antimicrobial approaches. The authors are convinced that even though the combined efficacy of aPDI and antimicrobials could be investigated with the wide range of methods, the use of a unified experimental methodology that is in agreement with antimicrobial susceptibility testing (AST) is required to investigate possible synergistic cooperation between aPDI and antimicrobials. Conclusions concerning the possible synergistic activity between the two treatments can be drawn only when appropriate assays are employed. It must be noticed that some of the described papers were just aimed at determination if combined treatments exert enhanced antibacterial outcome, without following the standard methodology to evaluate the synergistic effect, but in most of them (18 out of 27) authors indicated the existence of synergy between described antibacterial approaches. In general, the increase in bacterial inactivation was observed when both therapies were used in combination.

An In Vitro Model to Study the Effect of 5-Aminolevulinic Acid-mediated Photodynamic Therapy on Staphylococcus aureus Biofilm

Staphylococcus aureus (S. aureus) is a common human pathogen, which causes pyogenic and systemic infections. S. aureus infections are difficult to eradicate not only due to the emergence of antibiotic-resistant strains but also its ability to form biofilms. Recently, photodynamic therapy (PDT) has been indicated as one of the potential treatments for controlling biofilm infections. However, further studies are required to improve our knowledge of its effect on bacterial biofilms, as well as the underlying mechanisms. This manuscript describes an in vitro model of PDT with 5-aminolevulinic acid (5-ALA), a precursor of the actual photosensitizer, protoporphyrin IX (PpIX). Briefly, mature S. aureus biofilms were incubated with ALA and then exposed to light. Subsequently, the antibacterial effect of ALA-PDT on S. aureus biofilm was quantified by calculating the colony forming units (CFUs) and visualized by viability fluorescent staining via confocal laser scanning microscopy (CLSM). Representative results demonstrated a strong antibacterial effect of ALA-PDT on S. aureus biofilms. This protocol is simple and can be used to develop an in vitro model to study the treatment of S. aureus biofilms with ALA-PDT. In the future, it could also be referenced in PDT studies utilizing other photosensitizers for different bacterial strains with minimal adjustments.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Sensitizing Clostridium difficile Spores with Germinants on Skin and Environmental Surfaces Represents a New Strategy for Reducing Spores via Ambient Mechanisms

Background

Clostridium difficile is a leading cause of healthcare-associated infections worldwide. Prevention of C. difficile transmission is challenging because spores are not killed by alcohol-based hand sanitizers or many commonly used disinfectants. One strategy to control spores is to induce germination, thereby rendering the spores more susceptible to benign disinfection measures and ambient stressors.

Methods/Results

C. difficile spores germinated on skin after a single application of cholic acid-class bile salts and co-germinants; for 4 C. difficile strains, recovery of viable spores from skin was reduced by ~0.3 log₁₀CFU to 2 log₁₀CFU after 2 hours and ~1 log₁₀CFU to > 2.5 log₁₀CFU after 24 hours. The addition of taurocholic acid to 70% and 30% ethanol significantly enhanced reduction of viable spores on skin and on surfaces. Desiccation, and to a lesser extent the presence of oxygen, were identified as the stressors responsible for reductions of germinated spores on skin and surfaces. Additionally, germinated spores became susceptible to killing by pH 1.5 hydrochloric acid, suggesting that germinated spores that remain viable on skin and surfaces might be killed by gastric acid after ingestion. Antibiotic-treated mice did not become colonized after exposure to germinated spores, whereas 100% of mice became colonized after exposure to the same quantity of dormant spores.

Conclusions

Germination could provide a new approach to reduce C. difficile spores on skin and in the environment and to render surviving spores less capable of causing infection. Our findings suggest that it may be feasible to develop alcohol-based hand sanitizers containing germinants that reduce spores on hands.

A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection

In spite of increased awareness and the efforts taken to optimize Clostridium difficile infection (CDI) management, with the limited number of currently available antibiotics for C. difficile the halt of this increasing epidemic remains out of reach. There are, however, close to 80 alternative treatment methods with controversial anti-clostridial efficacy or in experimental phase today. Indeed, some of these therapies are expected to become acknowledged members of the recommended anti-CDI arsenal within the next few years. None of these alternative treatment methods can respond in itself to all the major challenges of CDI management, which are primary prophylaxis in the susceptible population, clinical cure of severe cases, prevention of recurrences, and forestallment of asymptomatic C. difficile carriage and in-hospital spread. Yet, the greater the variety of treatment choices on hand, the better combination strategies can be developed to reach these goals in the future. The aim of this article is to provide a comprehensive summary of these experimental and currently off-label therapeutic options.

The potential of photodynamic therapy (PDT)-Experimental investigations and clinical use

Photodynamic therapy (PDT) is an intensively studied part of medicine based on free radicals. These reactive species, extremely harmful for whole human organism, are used for eradication numerous diseases. Specific structure of ill tissues causes accumulation free radicals inside them without attack remaining healthy tissues. A rapid development of medicine and scientific research has led to extension of PDT towards treatment many diseases such as cancer, herpes, acne and based on antimicrobials. The presented review article is focused on the aforementioned disorders with accurate analysis of the newest available scientific achievements. The discussed cases explicitly indicate on high efficacy of the therapy. In most cases, free radicals turned out to be solution of many afflictions. Photodynamic therapy can be considered as promising treatment with comparable effectiveness but without side effects characteristic for chemotherapy.