Photosensitized inactivation of E. coli cells in toluidine blue-light system

Role of Toluidine Blue-O Binding Mechanism for Photooxidation in Bioinspired Bacterial Membranes

The alarming increase in bacterial resistance to antibiotics has demanded new strategies for microbial inactivation, which include photodynamic therapy whose activity relies on the photoreaction damage to the microorganism membrane. Herein, the binding mechanisms of the photosensitizer toluidine blue-O (TBO) on simplified models of bacterial membrane with Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) were correlated to the effects of the photoinduced lipid oxidation. Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were also used as a reference of mammalian membranes. The surface pressure isotherms combined with polarization-modulated infrared reflection absorption spectroscopy revealed that TBO expands DOPC, DOPE, and DOPG monolayers owing to electrostatic interactions with the negatively charged groups in the phospholipids, with a stronger adsorption on DOPG, which has a net surface charge. Light irradiation made the TBO-containing DOPC and DOPE monolayers less unstable as a result of the singlet oxygen (¹O₂) reaction with the chain unsaturation and hydroperoxide formation. In contrast, the decreased stability of the irradiated TBO-containing DOPG monolayer suggests the cleavage of carbon chains. The anionic nature of DOPG allowed a deeper penetration of TBO into the chain region, favoring contact-dependent reactions between the excited triplet state of TBO and lipid unsaturations or/and hydroperoxide groups, which is the key for the cleavage reactions and further membrane permeabilization.

Indocyanine Green-Mediated Photodynamic Therapy Reduces Methicillin-Resistant Staphylococcus aureus Drug Resistance

Methicillin-resistant Staphylococcus aureus (MRSA) skin-wound infections are associated with considerable morbidity and mortality. Indocyanine green (ICG), a safe and inexpensive dye used in clinical imaging, can be activated by near-infrared in photodynamic therapy (PDT) and photothermal therapy (PTT) to effectively kill MRSA. However, how this treatment affects MRSA drug sensitivity remains unknown. The drug-sensitivity phenotypes, bacterial growth rate, and cell-wall thickness of three MRSA strains were analyzed after ICG-PDT. Drug-resistant gene expressions were determined by polymerase chain reaction (PCR) and quantitative reverse transcription (qRT)-PCR. Related protein expressions were examined with immunoblotting. Drug sensitivity was further evaluated in animal models. MRSA that survived the treatment grew faster, and the cell wall became thinner compared to parental cells. These cells became more sensitive to oxacillin, which was partly related to mecA complex gene deletion. Skin necrosis caused by ICG-PDT-treated MRSA infection was smaller and healed faster than that infected with parental cells. With oxacillin therapy, no bacteria could be isolated from mouse lung tissue infected with ICG-PDT-treated MRSA. ICG-PDT drives MRSA toward an oxacillin-sensitive phenotype. It has the potential to develop into an alternative or adjuvant clinical treatment against MRSA wound infections.

Discovering the mechanisms of strain-dependent response of Staphylococcus aureus to photoinactivation: oxidative stress toleration, endogenous porphyrin level and strain's virulence

BACKGROUND

Staphylococcus aureus is generally known to be susceptible to photoinactivation. However, the phenomenon of its strain-dependent response to photodynamic treatment has been reported. Moreover, the factors determining the emerging variation among strains according to photoinactivation remain unclear.

METHODS

This work aimed to investigate any relevant correlation between bacterial toleration of oxidative stress, porphyrin level, photosensitizer uptake and strain's virulence of studied methicillin-susceptible and methicillin-resistant S. aureus strains and their response to photodynamic inactivation (using protoporphyrin diarginate, toluidine blue O and 5-aminolevulinic acid).

RESULTS

Obtained data let to demonstrate that studied factors have limited impact on strain response to PDI. However, we have shown that multicomponent sensitizing agent i.e. consisted of PPArg2, ALA and TBO would eliminate the S. aureus elevated resistance to photoinactivation and that both highly virulent and low virulent S. aureus strains could be easily eradicated with the use of PDI. Moreover, we have shown that photodynamic inactivation could decrease the virulence of S. aureus extracellular fraction.

CONCLUSION

The mechanism underlying strain-dependent response to photoinactivation is complex and multifactorial nevertheless with the use of several sensitizing agents the elevated resistance to photodynamic treatment can be omitted.

Laser light combined with a photosensitizer may eliminate methicillin-resistant strains of Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital acquired infection throughout the world especially in wound and burn infections, pneumonia, septicaemia and endocarditis. We describe the effect of a HeNe laser in combination with a TBO dye on the viability of MRSA. A total of 34 isolates of S. aureus were obtained from 100 patients suffering from burns or wounds and from the nasal vestibulum of medical and nonmedical staff as carriers; eight isolates were methicillin-resistant. The isolates were exposed for 5, 10 and 15 min to a HeNe laser at a wavelength of 632.8 nm and 7.5 mW output power in the presence of 50 microg/ml toluidune blue O photosensitizer. The viable count was substantially decreased as determined by the plate count method for the three exposure times, with 100% killing with the 15-min exposure time. No significant effect was observed on MRSA isolates exposed to the laser alone. So MRSA was completely eradicated following 15 min exposure to a 632.8-nm HeNe laser in the presence of 50 microg/ml toluidune blue O photosensitizer under in vitro conditions.

Toluidine blue O photodynamic inactivation on multidrug-resistant Pseudomonas aeruginosa

BACKGROUND AND OBJECTIVES

Multidrug-resistant (MDR) Pseudomonas aeruginosa infection is becoming a critical problem worldwide. Currently, only limited therapeutic options are available for the treatment of infections caused by MDR P. aeruginosa, therefore, the development of new alternative treatments is needed. Toluidine blue O (TBO) is an effective antibacterial photosensitizing agent against various bacteria. However, reports on antibacterial photosensitization of MDR bacteria are limited. This study aims to determine the in vitro photobactericidal activity of TBO against MDR P. aeruginosa.

STUDY DESIGN/MATERIALS AND METHODS

The efficacy of antibacterial photodynamic inactivation, DNA fragmentation and protein carbonylation of three MDR P. aeruginosa strains and one susceptible strain was compared using TBO as the photosensitizer followed by red light irradiation (630 nm, 90 J/cm(2)) from a light-emitting diode light source. Subsequently, the efficacy of TBO photodynamic inactivation (TBO-PDI) on 60 MDR strains, including 11 with the efflux pump phenotype and 49 with no pump activity, was tested using the minimum lethal drug concentration (MLC) assay.

RESULTS

TBO-PDI caused similar bactericidal effect (6-7 logs of killing effect), DNA fragmentation and protein carbonylation in three MDR and one susceptible P. aeruginosa strains. Although the TBO accumulation assay indicated that TBO is a substrate for the efflux pump, TBO-PDI produce similar photobactericidal activity against 60 MDR P. aeruginosa strains, either with or without efflux-pump phenotype, and 19 susceptible strains.

CONCLUSION

MDR did not affect the susceptibility of P. aeruginosa strains to TBO-PDI. The efflux pump played an insignificant role in TBO-PDI of MDR P. aeruginosa.

Anti-microbial photodynamic therapy: useful in the future?

Previous chapters in this volume have focused on fundamental principles and clinical applications of PDT. This chapter will attempt to outline emerging areas of research to identify some new applications that may become useful in the future in clinical practise. The worldwide rise in antibiotic resistance has driven research to the development of novel anti-microbial strategies. Cutaneous diseases caused by MRSA are ideally suited to treatment by anti-microbial photodynamic therapy for eradicating localized infections and for modulating wound healing due to the ability to deliver photosensitizer and light with topical application. The use of photosensitizer and light as an anti-microbial agent against periodontal microbial biofilms should also represent an attractive method of eliminating oral bacteria. Suitable light sources, laser light and non-coherent light will be briefly covered. This chapter will focus on some aspects of anti-microbial photodynamic therapy that appear to be promising for dermatological indications and inactivation of pathogenic bacteria within the oral cavity.

Methylene blue in photodynamic therapy: From basic mechanisms to clinical applications

Methylene blue (MB) is a molecule that has been playing important roles in microbiology and pharmacology for some time. It has been widely used to stain living organisms, to treat methemoglobinemia, and lately it has been considered as a drug for photodynamic therapy (PDT). In this review, we start from the fundamental photophysical, photochemical and photobiological characteristics of this molecule and evolved to show in vitro and in vivo applications related to PDT. The clinical cases shown include treatments of basal cell carcinoma, Kaposi's Sarcoma, melanoma, virus and fungal infections. We concluded that used together with a recently developed continuous light source (RL50(®)), MB has the potential to treat a variety of cancerous and non-cancerous diseases, with low toxicity and no side effects.

Photo-Activated Disinfection Of The Root Canal: A New Role For Lasers In Endodontics

Because micro-organisms play a crucial role in the development of pulpal and periapical disease, the prognosis of endodontic therapy is intimately related to the presence of bacteria within the root canal system. Micro-organisms may persist in the apical region of the root canal system despite chemomechanical preparation. The usefulness of Class IV lasers (such as Nd:YAG, diode, KTP and Er:YAG) for photo-thermal disinfection of the root canal has been demonstrated in numerous studies. An alternative approach to microbial killing in the root canal system by laser light involves the use of low-power lasers to drive a photochemical reaction that produces reactive oxygen species, a technique termed photo-activated disinfection (PAD). By using exogenous photosensitisers such as tolonium chloride, killing of all types of bacteria can be achieved. In vitro studies of PAD have demonstrated its ability to kill photosensitised oral bacteria (such as E. faecalis), and more recently microbial killing in vivo in the root canal system has been demonstrated. While PAD can be undertaken as part of the routine disinfection of the root canal system, it also has potential use for eradicating persistent endodontic infections for which conventional methods have been unsuccessful.

The phototoxicity of phenothiazinium derivatives against Escherichia coli and Staphylococcus aureus

Phenothiazinium dyes, and derivatives, were tested for toxicity to Escherichia coli and Staphylococcus aureus. The dyes were generally lipophilic (log P>1) and showed inherent dark toxicity (minimum lethal concentrations: 3.1-1000 microM). Dye illumination (total light dose of 3.15 J cm(-1) over 30 min) led to up to eight-fold reductions in minimum lethal concentrations. Most of the illuminated dyes showed significant relative singlet oxygen yields (phi'delta: 0.18-1.35) suggesting a type II mechanism of generating a phototoxic response. Although generally up to six-fold more effective against S. aureus, the dyes tested efficiently killed E. coli and may be of particular use in combating Gram-negative pathogens.

Factors influencing the susceptibility of Gram-negative bacteria to toluidine blue O-mediated lethal photosensitization

AIMS

Bacteria can be killed by red light in the presence of a photosensitizer. The purpose of this study was to evaluate the effect of physiological and environmental factors on the susceptibility of some bacteria associated with oral infections in immunocompromised patients to killing by the photosensitizer toluidine blue O (TBO).

METHODS AND RESULTS

Suspensions of Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae in human saliva, horse serum or saline were exposed to light from a helium/ neon laser in the presence of TBO. Additional suspensions at various growth phases and pHs were treated in an identical manner. Survivors were enumerated by viable counting. All three species were susceptible to lethal photosensitization under all of the conditions tested. The presence of serum and, to a lesser extent, saliva decreased the level of kill attained. The bactericidal effect was reduced at acid pHs but was unaffected by the growth phase of the organism.

CONCLUSIONS

The composition and pH of the fluid in which bacteria are suspended influenced the effectiveness of TBO-mediated lethal photosensitization, whereas killing was unaffected by the growth phase of the organism.

SIGNIFICANCE AND IMPACT OF THE STUDY

Environmental factors operating in the mouths of patients with mucositis could reduce the effectiveness of TBO-mediated lethal photosensitization of bacteria associated with this condition.

Comparison of the methylene blue and toluidine blue photobactericidal efficacy against gram-positive and gram-negative microorganisms

BACKGROUND AND OBJECTIVE

Studies on the photobactericidal efficacy of methylene blue (MB) and toluidine blue (TB) have shown inconsistent results in the literature. This study evaluated the bactericidal efficacy of MB and TB against different bacteria under light and dark conditions to determine the most effective bactericidal dye.

STUDY DESIGN/MATERIALS AND METHODS

Suspensions of Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, Hemophilus influenzae, Escherichia coli, and Pseudomonas aeruginosa in saline were treated in dark and red laser light conditions in the presence of each dye using an argon pumped-dye and a diode laser emitting light at 630 and 664 nm, respectively. The effect of dye concentration, dark incubation time, the fluence and intensity of laser light on the destruction of different bacteria were compared.

RESULTS

Both dyes eradicated all examined bacteria under laser light. The complete photodestruction of microorganisms was reached at TB concentrations of 1.5-7-fold less than that of MB.

CONCLUSION

TB exhibits a greater bactericidal activity than MB against most bacteria in dark and light conditions. Mostly, these results are consistent with their respective dye partition coefficients.

Methylene blue derivatives--suitable photoantimicrobials for blood product disinfection?

Photodynamic antimicrobial agents based on the well-established phenothiazinium biological stain methylene blue offer a simple method for the inactivation or destruction of pathogens contained in donated blood and blood products. The technique is currently concentrated on viruses and the disinfective procedure can be carried out in blood bags using basic low-power light sources. Pathogens of the bacterial, yeast and protozoal classes are also susceptible to phenothiaziniums. The photoantimicrobial mode of action is usually via oxidative damage to cellular components, either due to redox reactions between the agent and a biomolecular target or by the action of reactive oxygen species generated in situ by photodynamic action. The targeting of various microbial species is discussed in relation to the physicochemical make-up of the photosensitizers, and future directions are suggested.

A study of photobactericidal activity in the phenothiazinium series

The photodynamic antibacterial properties of a closely related series of commercially available phenothiazinium dyes were tested against a range of pathogenic strains of Gram-positive (Staphylococcus aureus, Enterococcus faecalis, Bacillus cereus) and Gram-negative organisms (Escherichia coli, Pseudomonas aeruginosa). The photosensitisers were illuminated using a non-laser light source at a fluence of 1.75 mW cm-2 and this resulted in the enhancement of antibacterial activity in liquid culture. In several cases, illumination resulted in considerable decreases in the minimum lethal concentrations required, giving up to 100-fold increases in bactericidal activity.

Photochemical interactions of methylene blue and analogues with DNA and other biological substrates

The light-induced reactions of methylene blue and related phenothiazinium dyes with biological substrates are described. The properties of the excited states of the dyes, their reactions with nucleic acids and their photosensitised chemical modifications of nucleic acid bases are examined. Reports on phenothiazinium dye-induced damage to proteins, lipids, biological membranes, organelles, viruses, bacteria, mammalian cells and carcinomas are reviewed.

Oxygen radicals are generated by dye-mediated intracellular photooxidations: a role for superoxide in photodynamic effects

Representative thiazines, xanthenes, acridines, and phenazines photosensitized the oxidation of reduced pyridine nucleotides and reduced glutathione when illuminated with low intensity visible light. Photooxidation resulted in oxygen consumption and in superoxide generation, assayed as the superoxide dismutase (SOD)-inhibitable reduction of ferricytochrome c. The major pathway of electron transfer involved dye reduction rather than singlet oxygen-mediated oxidation of the substrate, as demonstrated by the relative insensitivity of the oxidation to inhibition by sodium azide and by the observable bleaching of the dye. Hydrogen peroxide was a stable end product of photooxidation. Photosensitive dyes were photoreduced intracellularly. These dyes were transported across the membranes of Escherichia coli B and stimulated a light- and concentration-dependent increase in the cyanide-insensitive respiration. Dyes reduced intracellularly subsequently diffused out of the cell where they reduced extracellular cytochrome c. The photosensitive dyes examined in this study exhibited a light-dependent bacteriostatic effect on E. coli B grown in nutrient broth, manifested as an increased lag prior to growth. Restoration of growth coincided with increased levels of SOD, and the intracellular level of SOD correlated with the level of illumination, the dye concentration, and the reactivity of the dye to NADH in vitro. The thiazine dye, toluidine blue o, imposed a light- and oxygen-dependent lethality on E. coli B grown in glucose minimal medium. Toxicity was relieved by hydroxyl radical scavengers, and their ability to protect the cells was proportional to their reactivity with the hydroxyl radical. The results indicate that oxygen radicals and related species mediate photodynamic effects in E. coli B.

Photomodification of biological membranes with emphasis on singlet oxygen mechanisms

This review discusses photomodification of biological membranes and model membrane systems. Current concepts of membrane structure are first reviewed briefly. The role of preillumination association of sensitizer with membranes as it relates to photomodification rate is discussed, as well as the role of singlet oxygen in membrane photomodification. Finally the characteristics of singlet oxygen generation in membranes are considered. The evidence clearly indicates that membrane photomodification cannot be understood based only on the properties of sensitizers and singlet oxygen in aqueous solution. Rather the properties of sensitizers in association with membranes are the determinants of membrane photomodifcation. These properties differ significantly in aqueous solution and in membranes.

Relaxation of supercoiled plasmid DNA by oxidative stresses in Escherichia coli

The relaxation of plasmid DNA was observed after the visible light irradiation of Escherichia coli AB1157 harboring plasmid pBR322 or some other plasmids in the presence of a photosensitizing dye, such as toluidine blue or acridine orange, and molecular oxygen. Treatment of the cells with hydroperoxides, such as tert-butyl hydroperoxide, cumene hydroperoxide, and hydrogen peroxide, also caused the plasmid DNA relaxation in vivo. Relaxation was not observed in these treatments of purified pBR322 DNA in vitro. Plasmid DNA relaxation was also detected after near-UV irradiation. Far-UV irradiation did not induce such relaxation.

Gene responsible for protecting Escherichia coli from sodium dodecyl sulfate and toluidine blue plus light

Escherichia coli cells were killed by visible light irradiation in the presence of the photosensitizing dye, toluidine blue. Two uvrB mutant strains of E. coli K-12 (AB1885 and N3-1) were much more sensitive than the isogenic uvrA and uvrC strains to treatment with toluidine blue plus light, suggesting that the uvrB+ gene product was involved in repair of DNA damage induced by the treatment. The uvrB+ gene cloned in a high- or low-copy-number plasmid was transformed into the uvrB strain (AB1885). Although all the transformants showed the same resistance as its wild-type strain (AB1157) to UV irradiation, they were as sensitive as AB1885 was to treatment with toluidine blue plus light. The two uvrB strains were more sensitive to sodium dodecyl sulfate than the other strains, suggesting that these strains had a defect in the cell surface. A sodium dodecyl sulfate-resistant revertant obtained from AB1885 was more resistant than AB1885 was to treatment with toluidine blue plus light. The two uvrB strains (AB1885 and N3-1) appear to have a defective gene (tentatively called dvl) different from uvrB. Its map position was around 7 min on the E. coli map.