Photodynamic destruction of Haemophilus parainfluenzae by endogenously produced porphyrins

Acquiring of photosensitivity by Mycobacterium tuberculosis in vitro and inside infected macrophages is associated with accumulation of endogenous Zn-porphyrins

Mycobacterium tuberculosis (Mtb) is able to transition into a dormant state, causing the latent state of tuberculosis. Dormant mycobacteria acquire resistance to all known antibacterial drugs and can survive in the human body for decades before becoming active. In the dormant forms of M. tuberculosis, the synthesis of porphyrins and its Zn-complexes significantly increased when 5-aminolevulinic acid (ALA) was added to the growth medium. Transcriptome analysis revealed an activation of 8 genes involved in the metabolism of tetrapyrroles during the Mtb transition into a dormant state, which may lead to the observed accumulation of free porphyrins. Dormant Mtb viability was reduced by more than 99.99% under illumination for 30 min (300 J/cm2) with 565 nm light that correspond for Zn-porphyrin and coproporphyrin absorptions. We did not observe any PDI effect in vitro using active bacteria grown without ALA. However, after accumulation of active cells in lung macrophages and their persistence within macrophages for several days in the presence of ALA, a significant sensitivity of active Mtb cells (ca. 99.99%) to light exposure was developed. These findings create a perspective for the treatment of latent and multidrug-resistant tuberculosis by the eradication of the pathogen in order to prevent recurrence of this disease.

The influence of growth medium on the photodynamic susceptibility of Aggregatibacter actinomycetemcomitans to antimicrobial blue light

The aim of this study was to investigate whether antimicrobial blue light (aBL) can cause the death of Aggregatibacter actinomycetemcomitans (A.a) and to determine the influence of different culture media, specifically brain heart infusion and blood agar, on bacterial survival fraction. An LED emitting at 403 ± 15 nm, with a radiant power of 1W, irradiance of 588.2 mW/cm2, and an irradiation time of 0 min, 1 min, 5 min, 10 min, 30 min, and 60 min, was used. The plates were incubated in microaerophilic conditions at 37 °C for 48 h, and the colony-forming units were counted. The photosensitizers were investigated using spectroscopy and fluorescence microscopy. There was no significant difference between the culture media (p > 0.05). However, a statistical reduction in both media was observed at 30 min (1058 J/cm2) (p < 0.05). The findings of this study suggest that aBL has the potential to kill bacteria regardless of the culture media used. Light therapy could be a promising and cost-effective strategy for preventing periodontal disease when used in combination with mechanical plaque control.

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

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

Corynebacterium jeikeium Dormant Cell Formation and Photodynamic Inactivation

Pathogenic non-spore forming bacteria enter a dormant state under stressful conditions, which likely allows them to acquire resistance to various antibiotics. This work revealed the efficient formation of dormant "non-culturable" (NC) Corynebacterium jeikeium cells in stationary phase upon gradual acidification of the growth medium. Such cells were unable to form colonies and existed in a prolonged stationary phase. At an early stage of dormancy (approximately 14 days post-inoculation), dormant cells are able for resuscitation in liquid medium. However, those stored for long time in dormant state needed addition of supernatant taking from active C. jeikeium cultures for successful resuscitation. NC cells possessed low RNA synthesis and significant tolerance to antibiotics (rifampicin and vancomycin). They also accumulated free porphyrins, and 5-aminolevulinic acid addition enhanced free porphyrin accumulation which makes them potentially sensitive to photodynamic inactivation (PDI). PDI of dormant bacteria was accomplished by exposing cells to a 565 nm wavelength of light using a SOLIS-4C light-emitting diode for 60 min. This revealed that increased porphyrin concentrations were correlated with elevated PDI sensitivity. Results shown here demonstrate the potential utility of employing PDI to minimize levels of dormant, persistent corynebacteria and the C. jeikeium dormancy model developed here may be useful for finding new drugs and techniques for combatting persistent corynebacteria.

Photodynamic inactivation mediated by 5-aminolevulinic acid of bacteria in planktonic and biofilm forms

Bacterial photodynamic inactivation (PDI) employing endogenous production of porphyrins from 5-aminolevulinic acid (ALA) - named ALA-PDI-, is a new promising tool to achieve bacteria control in non-spread infections. The technique combines the action of the porphyrins acting as photosensitisers with light, to produce reactive oxygen species to target the pathogen. To date, some clinical applications of ALA-PDI have been reported although variable responses ranging from total eradication to absence of photokilling were found. ALA-PDI conducted at suboptimal conditions may lead to misleading results and the complexity of haem synthesis in bacteria hinders the optimization of the treatment. The present work aimed to gain insight on the variables affecting ALA-PDI in Gram-positives and Gram-negatives bacteria growing on planktonic and biofilm cultures and to correlate the degree of the response with the amount and type of porphyrin synthesised. Staphylococcus epidermidis and Escherichia coli clinical isolates and Pseudomonas aeruginosa ATCC27853 and Staphylococcus aureus ATCC25923 strains were utilised, and the optimal conditions of concentration and time exposure of ALA, and light dose were set. In both Gram-positive species analysed, a peak of porphyrin synthesis was observed at 1-2 mM ALA in biofilm and planktonic cultures, which fairly correlated with the decrease in the number of CFU after PDI (5 to 7 logs) and porphyrin content was in the same order of magnitude. In addition, ALA-PDI was similarly effective for planktonic and biofilm S. aureus cultures, and more effective in S. epidermidis planktonic cultures at low light doses. Beyond a certain light dose, it was not possible to achieve further photosensitization. Similarly, a plateau of cell death was attained at a certain ALA incubation time. Accumulation of hydrophilic porphyrins at longer incubation periods was observed. The proportion of porphyrins changed as a function of ALA concentration and incubation time in the Gram-positive bacteria, though we did not find a clear correlation between the porphyrin type and PDI response. As a salient feature was the presence of isococroporphyrin isoforms in both Gram-positive and Gram-negative bacteria. Gram-negative bacteria were quite refractory to the treatment: P. aeruginosa was slightly inactivated (4-logs reduction) at 40 mM ALA, whereas E. coli was not inactivated at all. These species accumulated high ALA quantities and the amount of porphyrins did not correlate with the degree of photoinactivation. Our microscopy studies show that porphyrins are not located in the envelopes of Gram-negative bacteria, reinforcing the hypothesis that endogenous porphyrins fail to attack these structures.

Photoinactivation of dormant Mycobacterium smegmatis due to its endogenous porphyrins

Mycobacterium tuberculosis is able to transition into a dormant state, causing a latent state of tuberculosis. Dormant mycobacteria acquire phenotypic resistance to all known antibacterial drugs; they are also able to maintain vitality in the host for decades and become active, causing the active form of the disease. In order to cure latent tuberculosis, new approaches should be developed. Earlier, we discovered accumulation in significant concentrations of porphyrins in dormant Mycobacterium smegmatis, which is a close, fast-growing relative of the causative agent of tuberculosis. In this study, we explore a new possibility to kill dormant mycobacteria by photodynamic inactivation (PDI) using accumulated porphyrins as endogenous photosensitisers. The dormant M. smegmatis were obtained under gradual acidification in Sauton's medium, for 14 days. Cells were exposed to light with different wavelengths emitted by three Spectra X light-emitting diodes (395/25, 470/24, 575/25 nm) and one separated 634-nm LED for 15 min. An increase in the concentration of coproporphyrin in M. smegmatis after 6 days of growth correlated with the beginning of a decrease in metabolic activity and formation of ovoid dormant forms. Dormant bacteria were sensitive to PDI and killed after 15-30 min of illumination, in contrast to active cells. The greatest inactivation of dormant mycobacteria occurred at 395 and 575 nm, which coincides with the main maximum of the absorption spectrum of extracted porphyrins. We, for the first time, demonstrate a successful application of PDI for inactivation of dormant mycobacteria, due to significant accumulation of endogenous photosensitisers-porphyrins.

Sensitization of Salmonella enterica with 5-aminolevulinic acid-induced endogenous porphyrins: a spectroscopic study

The fluorescence spectroscopy data reflecting time-dependent changes in the type and localization of endogenous porphyrins reveal the sensitization potential of a precursor 5-ALA for Gram-negative foodborne pathogen Salmonella enterica.

Light as a Broad-Spectrum Antimicrobial

Antimicrobial resistance is a significant and growing concern. To continue to treat even simple infections, there is a pressing need for new alternative and complementary approaches to antimicrobial therapy. One possible addition to the current range of treatments is the use of narrow-wavelength light as an antimicrobial, which has been shown to eliminate a range of common pathogens. Much progress has already been made with blue light but the potential of other regions of the electromagnetic spectrum is largely unexplored. In order that the approach can be fully and most effectively realized, further research is also required into the effects of energy dose, the harmful and beneficial impacts of light on eukaryotic tissues, and the role of oxygen in eliciting microbial toxicity. These and other topics are discussed within this perspective.

Photo Inactivation of Streptococcus mutans Biofilm by Violet-Blue light

Among various preventive approaches, non-invasive phototherapy/photodynamic therapy is one of the methods used to control oral biofilm. Studies indicate that light at specific wavelengths has a potent antibacterial effect. The objective of this study was to determine the effectiveness of violet-blue light at 380-440 nm to inhibit biofilm formation of Streptococcus mutans or kill S. mutans. S. mutans UA159 biofilm cells were grown for 12-16 h in 96-well flat-bottom microtiter plates using tryptic soy broth (TSB) or TSB with 1 % sucrose (TSBS). Biofilm was irradiated with violet-blue light for 5 min. After exposure, plates were re-incubated at 37 °C for either 2 or 6 h to allow the bacteria to recover. A crystal violet biofilm assay was used to determine relative densities of the biofilm cells grown in TSB, but not in TSBS, exposed to violet-blue light. The results indicated a statistically significant (P < 0.05) decrease compared to the non-treated groups after the 2 or 6 h recovery period. Growth rates of planktonic and biofilm cells indicated a significant reduction in the growth rate of the violet-blue light-treated groups grown in TSB and TSBS. Biofilm viability assays confirmed a statistically significant difference between violet-blue light-treated and non-treated groups in TSB and TSBS. Visible violet-blue light of the electromagnetic spectrum has the ability to inhibit S. mutans growth and reduce the formation of S. mutans biofilm. This in vitro study demonstrated that violet-blue light has the capacity to inhibit S. mutans biofilm formation. Potential clinical applications of light therapy in the future remain bright in preventing the development and progression of dental caries.

An insight on bacterial cellular targets of photodynamic inactivation

The emergence of microbial resistance is becoming a global problem in clinical and environmental areas. As such, the development of drugs with novel modes of action will be vital to meet the threats created by the rise in microbial resistance. Microbial photodynamic inactivation is receiving considerable attention for its potentialities as a new antimicrobial treatment. This review addresses the interactions between photosensitizers and bacterial cells (binding site and cellular localization), the ultrastructural, morphological and functional changes observed at initial stages and during the course of photodynamic inactivation, the oxidative alterations in specific molecular targets, and a possible development of resistance.

5-Aminolevulinic acid induced photodynamic inactivation on Staphylococcus aureus and Pseudomonas aeruginosa

The aim of the present study was to develop a simple and fast screening technique to directly evaluate the bactericidal effects of 5-aminolevulinic acid (ALA)-mediated photodynamic inactivation (PDI) and to determine the optimal antibacterial conditions of ALA concentrations and the total dosage of light in vitro. The effects of PDI on Staphylococcus aureus and Pseudomonas aeruginosa in the presence of various concentrations of ALA (1.0 mM, 2.5 mM, 5.0 mM, 10.0 mM) were examined. All bacterial strains were exponentially grown in the culture medium at room temperature in the dark for 60 minutes and subsequently irradiated with 630 ± 5 nm using a light-emitting diode (LED) red light device for accumulating the light doses up to 216 J/cm². Both bacterial species were susceptible to the ALA-induced PDI. Photosensitization using 1.0 mM ALA with 162 J/cm² light dose was able to completely reduce the viable counts of S. aureus. A significant decrease in the bacterial viabilities was observed for P. aeruginosa, where 5.0 mM ALA was photosensitized by accumulating the light dose of 162 J/cm². We demonstrated that the use of microplate-based assays—by measuring the apparent optical density of bacterial colonies at 595 nm—was able to provide a simple and reliable approach for quickly choosing the parameters of ALA-mediated PDI in the cell suspensions.

Persistence of Bacteroides ovatus under simulated sunlight irradiation

Background

Bacteroides ovatus, a member of the genus Bacteroides, is considered for use in molecular-based methods as a general fecal indicator. However, knowledge on its fate and persistence after a fecal contamination event remains limited. In this study, the persistence of B. ovatus was evaluated under simulated sunlight exposure and in conditions similar to freshwater and seawater. By combining propidium monoazide (PMA) treatment and quantitative polymerase chain reaction (qPCR) detection, the decay rates of B. ovatus were determined in the presence and absence of exogenous photosensitizers and in salinity up to 39.5 parts per thousand at 27°C.

Results

UVB was found to be important for B. ovatus decay, averaging a 4 log₁₀ of decay over 6 h of exposure without the presence of extracellular photosensitizers. The addition of NaNO₂, an exogenous sensitizer producing hydroxyl radicals, did not significantly change the decay rate of B. ovatus in both low and high salinity water, while the exogenous sensitizer algae organic matter (AOM) slowed down the decay of B. ovatus in low salinity water. At seawater salinity, the decay rate of B. ovatus was slower than that in low salinity water, except when both NaNO₂ and AOM were present.

Conclusion

The results of laboratory experiments suggest that if B. ovatus is released into either freshwater or seawater environment in the evening, 50% of it may be intact by the next morning; if it is released at noon, only 50% may be intact after a mere 5 min of full spectrum irradiation on a clear day. This study provides a mechanistic understanding to some of the important environmental relevant factors that influenced the inactivation kinetics of B. ovatus in the presence of sunlight irradiation, and would facilitate the use of B. ovatus to indicate the occurrence of fecal contamination.

Role of temperature and Suwannee River natural organic matter on inactivation kinetics of rotavirus and bacteriophage MS2 by solar irradiation

Although the sunlight-mediated inactivation of viruses has been recognized as an important process that controls surface water quality, the mechanisms of virus inactivation by sunlight are not yet clearly understood. We investigated the synergistic role of temperature and Suwannee River natural organic matter (SRNOM), an exogenous sensitizer, for sunlight-mediated inactivation of porcine rotavirus and MS2 bacteriophage. Upon irradiation by a full spectrum of simulated sunlight in the absence of SRNOM and in the temperature range of 14-42 °C, high inactivation rate constants, k(obs), of MS2 (k(obs) ≤ 3.8 h(-1) or 1-log(10) over 0.6 h) and rotavirus (k(obs) ≤ 11.8 h(-1) or ∼1-log(10) over 0.2 h) were measured. A weak temperature (14-42 °C) dependence of k(obs) values was observed for both viruses irradiated by the full sunlight spectrum. Under the same irradiation condition, the presence of SRNOM reduced the inactivation of both viruses due to attenuation of lower wavelengths of the simulated sunlight. For rotavirus and MS2 solutions irradiated by only UVA and visible light in the absence of SRNOM, inactivation kinetics were slow (k(obs) < 0.3 h(-1) or <1-log(10) unit reduction over 7 h) and temperature-independent for the range considered. Conversely, under UVA and visible light irradiation and in the presence of SRNOM, temperature-dependent inactivation of MS2 was observed. For rotavirus, the SRNOM-mediated exogenous inactivation was only important at temperatures >33 °C, with low rotavirus k(obs) values (k(obs) ≈ 0.2 h(-1); 1-log(10) unit reduction over 12 h) for the temperature range of 14-33 °C. These k(obs) values increased to 0.5 h(-1) at 43 °C and 1.5 h(-1) (1-log(10) reduction over 1.6 h) at 50 °C. While SRNOM-mediated exogenous inactivation of MS2 was triggered by singlet oxygen, the presence of hydrogen peroxide was important for rotavirus inactivation in the 40-50 °C range.

Photodynamic therapy based on 5-aminolevulinic acid and its use as an antimicrobial agent

Exogenous 5-aminolevulinic acid (ALA) is taken up directly by bacteria, yeasts, fungi, and some parasites, which then induces the accumulation of protoporphyrin IX (PPIX). Subsequent light irradiation of PPIX leads to the inactivation of these organisms via photodamage to their cellular structures. ALA uptake and light irradiation of PPIX produced by host cells leads to the inactivation of other parasites, along with some viruses, via the induction of an immune response. ALA-mediated PPIX production by host cells and light irradiation result in the inactivation of other viruses via either the induction of a host cell response or direct photodynamic attack on viral particles. This ALA-mediated production of light-activated PPIX has been extensively used as a form of photodynamic therapy (PDT) and has shown varying levels of efficacy in treating conditions that are associated with microbial infection, ranging from acne and verrucae to leishmaniasis and onychomycosis. However, for the treatment of some of these conditions by ALA-based PDT, the role of an antimicrobial effect has been disputed and in general, the mechanisms by which the technique inactivates microbes are not well understood. In this study, we review current understanding of the antimicrobial mechanisms used by ALA-based PDT and its role in the treatment of microbial infections along with its potential medical and nonmedical applications.

Therapeutic effect of photodynamic therapy using Na-pheophorbide a on osteomyelitis models in rats

OBJECTIVE

In this study, we examined the therapeutic effect of photodynamic therapy (PDT) using the photosensitizer Na-Pheophorbide a (Na-Phde a) on osteomyelitis models in rats.

BACKGROUND

Osteomyelitis is one of the most serious infectious problems in the orthopedic field. Recently, as a new clinical approach against septic arthritis, an experimental in vivo and in vitro model for the inactivation of methicillin-resistant-Staphylococcus aureus by PDT using Na-Phde a has been developed.

METHODS

Methicillin-sensitive Staphylococcus aureus (MSSA) was injected into the tibia of the rats to create osteomyelitis models (n = 10, 10 legs). A total of 560 μmol/l of Na-Phde a solution was injected into five of these tibial osteomyelitis models (five legs) 48 h after the initial MSSA infection. Sixty minutes after the Na-Phde a injection, a semiconductor laser (125 mW, 670 nm) was used to irradiate the models for 10 min with a total energy of 93.8 J/mm(2). As a control group, five rats (five legs) were treated with a phosphate buffered saline injection at 48 h after MSSA infection. Weight and leg perimeter changes were plotted. Bacterial growth, histological examination and radiological examination were evaluated at 14 days after initial treatment.

RESULTS

PDT with Na-Phde a significantly prevented leg swelling. In the PDT group, bone destruction owing to osteomyelitis was inhibited not only histologically but also radiographically.

CONCLUSIONS

The results in these experiments show that PDT using Na-Phde a improved osteomyelitis in rats. This suggests that PDT using Na- Phde a can be a useful treatment for osteomyelitis.

Bactericidal effect of photodynamic therapy using Na-pheophorbide a: evaluation of adequate light source

OBJECTIVE

To evaluate the efficacy of photodynamic therapy (PDT) against methicillin resistant-Staphylococcus aureus (MRSA) by selecting different light sources for irradiation and combining them with the photosensitizer Na-Pheophorbide a (Na-Phde a).

BACKGROUND

The treatment of drug-resistant bacterial infection is a serious issue. Recently, as a new clinical approach against septic arthritis, an experimental in vivo and in vitro model for the inactivation of MRSA by PDT using the photosensitizer Na-Phde a has been developed.

MATERIALS AND METHODS

Na-Phde a solution (280 micromol/L) was mixed with MRSA strain bacterial inoculum. After 60 minutes, light was irradiated for 30 minutes using the following light sources: GaA1p semiconductor laser (300 mW, 670 nm), halogen lamp (75 W), xenon lamp (300 W) and fluorescent lamp (27 W). Bacterial growth was evaluated after 24 hours incubation in a blood agar culture.

RESULTS

The semiconductor laser and halogen lamp groups showed perfect bactericidal effects after PDT. The xenon lamp and fluorescent lamp groups showed partial bactericidal effects.

CONCLUSIONS

The results of this experiment showed that PDT using the combination of Na-Phde a with a semiconductor laser or halogen lamp showed a better bactericidal performance than with xenon or fluorescent lamps. These findings indicated that PDT using Na-Phde a could be a useful treatment for septic arthritis and soft tissue infection.

Inactivation of bacterial pathogens following exposure to light from a 405-nanometer light-emitting diode array

This study demonstrates the susceptibility of a variety of medically important bacteria to inactivation by 405-nm light from an array of light-emitting diodes (LEDs), without the application of exogenous photosensitizer molecules. Selected bacterial pathogens, all commonly associated with hospital-acquired infections, were exposed to the 405-nm LED array, and the results show that both gram-positive and gram-negative species were successfully inactivated, with the general trend showing gram-positive species to be more susceptible than gram-negative bacteria. Detailed investigation of the bactericidal effect of the blue-light treatment on Staphylococcus aureus suspensions, for a range of different population densities, demonstrated that 405-nm LED array illumination can cause complete inactivation at high population densities: inactivation levels corresponding to a 9-log(10) reduction were achieved. The results, which show the inactivation of a wide range of medically important bacteria including methicillin-resistant Staphylococcus aureus, demonstrate that, with further development, narrow-spectrum 405-nm visible-light illumination from an LED source has the potential to provide a novel decontamination method with a wide range of potential applications.

The minimum influences for murine normal joint tissue by novel bactericidal treatment and photodynamic therapy using na-pheophorbide a for septic arthritis

OBJECTIVE

In this study, we examined the effect of photodynamic therapy (PDT) using Na-pheophorbide a (Na-Phde a) on normal joint tissue.

BACKGROUND DATA

The treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection is a serious issue. Recently, an experimental in vivo and in vitro model for the inactivation of MRSA by PDT using a photosensitizer, Na-Phde a, has been developed.

MATERIALS AND METHODS

The knee joints of mice were injected with 560 or 280 micromol/L of Na-Phde a. Thirty minutes after injection, percutaneous laser irradiation was applied for 5 min using a semiconductor laser (power: 125 mW; wavelength: 664 nm; total energy: 12 J/cm2). The joint perimeter and body weight of the treated mice were monitored, and histological evaluation was also done.

RESULTS

Joint swelling was observed up to 3 wk after PDT (p < 0.05). On histology 1 wk post-PDT, the treated knees were found to have inflammatory changes, primarily in synovial tissue. Eight weeks after PDT, the synovitis was no longer present. No significant effects were observed on cartilage, bone marrow, or menisci.

CONCLUSIONS

The results of this experiment showed that PDT with Na-Phde a induced arthritis for a short time after treatment. However, this arthritis was reversible, and the PDT did not appear to induce osteoarthritic changes in normal joint tissue. These findings indicate that PDT using Na-Phde a caused minimal but reversible changes in joint tissue, suggesting that it would be a safe and useful treatment for bacterial septic arthritis.

Use of merocyanine 540 for photodynamic inactivation of Staphylococcus aureus planktonic and biofilm cells

Photodynamic inactivation of Staphylococcus aureus planktonic and biofilm cells by a phtotosensitizer, merocyanine 540 (MC 540), was investigated. For the planktonic experiments, MC 540 binding efficiency to bacterial cells was found to increase with both increasing MC 540 concentration and increasing incubation time, but the binding became saturated following 10 min of incubation. The antimicrobial activity was enhanced with an increasing light dose, but an increase in the light dose could not further improve the antimicrobial activity if the maximum excitation level attainable was less than the necessary minimum threshold level. Complete inactivation was achieved when the excitation level of MC 540 was somewhere above the threshold level. The relationship between antimicrobial activity and the excitation level of MC 540 revealed that the more MC 540 was excited, the more S. aureus cells were killed. For the biofilm experiments, the antimicrobial activity was enhanced with an increase in the light dose. No viable cells were detected when organisms were exposed to 15 mug of MC 540 per ml and a light dose of 600 J/cm2 or to 20 mug of MC 540 per ml and a light dose of 450 J/cm2. A quantitative analysis of MC 540 bound to biofilms was also performed, and the images from confocal laser scanning microscopy provided direct evidence that revealed the difference between the MC 540 remaining in the biofilms prior to irradiation and the MC 540 remaining in the biofilms after irradiation. The results of both the planktonic and biofilm experiments suggest that the antimicrobial activity of photodynamic inactivation of S. aureus is closely related to the excitation level of MC 540.

Photodynamic therapy: a new antimicrobial approach to infectious disease?

Photodynamic therapy (PDT) employs a non-toxic dye, termed a photosensitizer (PS), and low intensity visible light which, in the presence of oxygen, combine to produce cytotoxic species. PDT has the advantage of dual selectivity, in that the PS can be targeted to its destination cell or tissue and, in addition, the illumination can be spatially directed to the lesion. PDT has previously been used to kill pathogenic microorganisms in vitro, but its use to treat infections in animal models or patients has not, as yet, been much developed. It is known that Gram-(-) bacteria are resistant to PDT with many commonly used PS that will readily lead to phototoxicity in Gram-(+) species, and that PS bearing a cationic charge or the use of agents that increase the permeability of the outer membrane will increase the efficacy of killing Gram-(-) organisms. All the available evidence suggests that multi-antibiotic resistant strains are as easily killed by PDT as naive strains, and that bacteria will not readily develop resistance to PDT. Treatment of localized infections with PDT requires selectivity of the PS for microbes over host cells, delivery of the PS into the infected area and the ability to effectively illuminate the lesion. Recently, there have been reports of PDT used to treat infections in selected animal models and some clinical trials: mainly for viral lesions, but also for acne, gastric infection by Helicobacter pylori and brain abcesses. Possible future clinical applications include infections in wounds and burns, rapidly spreading and intractable soft-tissue infections and abscesses, infections in body cavities such as the mouth, ear, nasal sinus, bladder and stomach, and surface infections of the cornea and skin.

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.

Treatment of cutaneous leishmaniasis by photodynamic therapy

BACKGROUND

Cutaneous leishmaniasis represents a common health problem and standard treatments are often ineffective or yield poor cosmetic results.

OBJECTIVE

We compared the efficacy of photodynamic therapy (PDT) with paromomycin sulfate in 10 lesions of cutaneous leishmaniasis.

METHODS

Five lesions were treated by PDT with Metvix (Photocure, Oslo, Norway) and 75 J/cm(2) red light. PDT was performed twice weekly and, after 12 weeks, once weekly. The other 5 lesions were treated with paromomycin sulfate once daily. All nonresponding lesions of the paromomycin-treated plaques finally also underwent PDT.

RESULTS

All 5 lesions treated by PDT and 2 of the paromomycin sulfate-treated plaques were clinically and histologically Leishmania free. Three lesions with poor response to paromomycin sulfate finally responded to subsequent PDT. Ten months after therapy there was no recurrence, and cosmetic outcome after PDT was excellent.

CONCLUSION

PDT may be an effective therapeutic alternative in cutaneous leishmaniasis.

Photoeradication of Helicobacter pylori using 5-aminolevulinic acid: preliminary human studies

BACKGROUND AND OBJECTIVES

Helicobacter pylori (HP) is an endemic pathogenic bacterium causing gastritis and gastroduodenal ulceration in humans and is linked to the development of gastric malignancies. These first human in vivo studies investigated the photoeradication of HP using laser and white light.

STUDY DESIGN/MATERIALS AND METHODS

In 13 HP-positive volunteers, a zone of gastric antrum was irradiated with laser (410 nm, 50 J/cm(2)) or endoscopic white light (10 J/cm(2)) 45 minutes after oral 5-aminolevulinic acid (5-ALA) 20 mg/kg. HP-eradication was assessed by biopsy urease test and HP-culture from irradiated and control zones 5 minutes, 4 and 48 hours post-irradiation.

RESULTS

A maximum eradication effect was achieved at 4 hours post-irradiation when 85% of biopsies in the monochromatic and 66% in the white light exposed zones, and 58 and 33% in the respective control zones were HP-negative.

CONCLUSIONS

HP numbers were greatly reduced following exposure to 5-ALA and either laser or white light in vivo. Photoeradication appears feasible, but further light dosimetry and the development of convenient application methods is required.

Eradication of Propionibacterium acnes by its endogenic porphyrins after illumination with high intensity blue light

Propionibacterium acnes is a Gram-positive, microaerophilic bacterium that causes skin wounds. It is known to naturally produce high amounts of intracellular porphyrins. The results of the present study confirm that the investigated strain of P. acnes is capable of producing endogenic porphyrins with no need for any trigger molecules. Extracts from growing cultures have demonstrated emission peaks around 612 nm when excited at 405 nm, which are characteristic for porphyrins. Endogenic porphyrins were determined and quantified after their extraction from the bacterial cells by fluorescence intensity and by elution retention time on high-performance liquid chromatography (HPLC). The porphyrins produced by P. acnes are mostly coproporphyrin, as shown by the HPLC elution patterns. Addition of delta-aminolevulinic acid (ALA) enhanced intracellular porphyrin synthesis and higher amounts of coproporphyrin have been found. Eradication of P. acnes by its endogenic porphyrins was examined after illumination with intense blue light at 407-420 nm. The viability of 24 h cultures grown anaerobically in liquid medium was reduced by less than two orders of magnitude when illuminated once with a light dose of 75 J cm(-2). Better photodynamic effects were obtained when cultures were illuminated twice or three times consecutively with a light dose of 75 J cm(-2) and an interval of 24 h between illuminations. The viability of the culture under these conditions decreased by four orders of magnitude after two illuminations and by five orders of magnitude after three illuminations. When ALA-triggered cultures were illuminated with intense blue light at a light dose of 75 J cm(-2) the viability of the treated cultures decreased by seven orders of magnitude. This decrease in viability can occur even after a single exposure of illumination for the indicated light intensity. X-ray microanalysis and transmission electron microscopy revealed structural damages to membranes in the illuminated P. acnes. Illumination of the endogenous coproporphyrin with blue light (407-420 nm) apparently plays a major role in P. acnes photoinactivation. A treatment protocol with a series of several illuminations or illumination after application of ALA may be suitable for curing acne. Treatment by both pathways may overcome the resistance of P. acnes to antibiotic treatment.

Fluorescence lifetime measurements of disulfonated aluminium phthalocyanine in the presence of microbial cells

The fluorescence lifetimes of disulfonated aluminium phthalocyanine (AlPcS2) in the presence of several different microbial cells are measured using the technique of time correlated single photon counting (TCSPC) employing front-face illumination. The microbes studied are: Escherichia coli, Porphyromonas gingivalis (Gram-negative bacteria), Streptococcus mutans (a Gram-positive bacterium), and the yeast Candida albicans. Complex fluorescence decays are observed when AlPcS2 is in the presence of these microbes; the fluorescence decay data can be fitted to a distribution of exponential lifetimes indicating that the AlPcS2 molecules experience a range of micro-environments The average fluorescence lifetimes of AlPcS2 in the presence of the microbes studied range from 4.85 to 5.95 ns, indicating differences in the cellular localisation of AlPcS2 with each of the microbes studied. These novel data are presented alongside a brief summary of existing AlPcS2 fluorescence lifetime data measured both in solution and in model biological systems.

delta-Aminolaevulinic acid-induced porphyrin synthesis and photodynamic inactivation of Escherichia coli B

The possibility and conditions for the induction of porphyrin synthesis by exogenous delta-aminolaevulinic acid (ALA) and its applicability for the inactivation of Gram-negative bacteria Escherichia coli B. by photodynamic therapy (PDT) have been studied. The bacteria are supplemented with ALA in the log phase of growth, and are grown in a synthetic medium at 37 degrees C in the dark. The efficiency of porphyrin synthesis is detected by fluorescence spectroscopy performed on the isolated bacterial cells and the medium, respectively, and compared with results of high-performance liquid chromatography (HPLC) analysis. ALA stimulates the synthesis of protoporphyrin in the bacteria by a factor of five to six, and an increased amount of the more hydrophilic derivatives with a significant contribution of mesoporphyrin by a factor of two to three is observed in the culturing medium. The optimal conditions of ALA treatment with respect to PDT are 10-15 min of incubation of a bacterial culture of 2 x 10(7) cells ml-1 with (5-9) x 10(-3) mol l-1 ALA. The ALA-treated cells are irradiated by white light of 80 mW cm-2 under growth conditions and a decrease to 0.6% of the number of colony-forming units (CFUs ml-1) is observed after 90 min of irradiation.

Endogenous porphyrin accumulation and photosensitization in the yeast Saccharomyces cerevisiae in the presence of 2,2'-dipyridyl

The chelator 2,2'-dipyridyl (0.2 mM) induces a remarkable increase of protoporphyrin IX concentration as well as of its Zn-containing complex in the yeast Saccharomyces cerevisiae. Endogenous porphyrin accumulation results in five- to six-fold cell sensitization to visible light (400-600 nm). Mitochondria isolated from the cells grown in the presence of 2,2'-dipyridyl accumulate protoporphyrin IX and Zn-protoporphyrin IX, while plasma membranes besides that exhibit porphyrin-type fluorescence at 670-675 nm in chloroform extract. The protoporphyrin IX content increases more than four-fold in mitochondria and two-fold in plasma membranes isolated from chelator-treated cells. The relative contribution of subcellular structure photodestruction to photoinduced cell inactivation is discussed.