Antimicrobial Photoinactivation

Virulence. 2011 Nov-Dec;2(6):509-20. Epub 2011 Nov 1.

All you need is light: antimicrobial photoinactivation as an evolving and emerging discovery strategy against infectious disease.

St Denis TG, Dai T, Izikson L, Astrakas C, Anderson RR, Hamblin MR, Tegos GP.


Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA.


The story of prevention and control of infectious diseases remains open and a series of highly virulent pathogens are emerging both in and beyond the hospital setting. Antibiotics were an absolute success story for a previous era. The academic and industrial biomedical communities have now come together to formulate consensus beliefs regarding the pursuit of novel and effective alternative anti-infective countermeasures. Photodynamic therapy was established and remains a successful modality for malignancies but photodynamic inactivation has been transformed recently to an antimicrobial discovery and development platform. The concept of photodynamic inactivation is quite straightforward and requires microbial exposure to visible light energy, typically wavelengths in the visible region, that causes the excitation of photosensitizer molecules (either exogenous or endogenous), which results in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation. It is an area of increasing interest, as research is advancing i) to identify the photochemical and photophysical mechanisms involved in inactivation; ii) to develop potent and clinically compatible photosensitizer; iii) to understand how photoinactivation is affected by key microbial phenotypic elements (multidrug resistance and efflux, virulence and pathogenesis determinants, biofilms); iv) to explore novel delivery platforms inspired by current trends in pharmacology and nanotechnology; and v) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants.

Mini Rev Med Chem.  Jul;9(8):974-83.

A new strategy to destroy antibiotic resistant microorganisms: antimicrobial photodynamic treatment.

Maisch T.


Antimicrobial PDT, Clinic and Polyclinic for Dermatology, Regensburg University Hospital, Germany, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany.


Photodynamic activity of chemical compounds towards microorganisms was first published at the turn of 20th century and it is based on the concept that a chemical compound, known as the photosensitizer, is localized preferentially in the microorganism and subsequently activated by low doses of visible light of an appropriate wavelength to generate reactive oxygen species that are toxic to the target microorganisms. Processes, in which absorption of light by a photosensitizer induces chemical changes in another molecule, are defined as photosensitizing reactions. Since the middle of the last century, antibacterial photosensitizing reactions were forgotten because of the discovery and the beginning of the Golden Age of antibiotics. Certainly, in the last decades the worldwide rise in antibiotic resistance has driven research to the development of new anti-microbial strategies. Different classes of molecules including phenothiazine, porphyrines, phthalocyanines, and fullerenes have demonstrated antimicrobial efficacy against a broad spectrum of antibiotic resistant microorganisms upon illumination. Due to their extended pi-conjugated system these molecules absorb visible light, have a high triplet quantum yield and can generate reactive oxygen species upon illumination. This mini-review will focus on some major advances regarding physical and chemical properties of photosensitizers and light sources that appear to be suitable in the field of antimicrobial photodynamic therapy. Currently, topical application of a photosensitizer on infected tissues and subsequent illumination seems to be the most promising feature of antimicrobial photodynamic therapy, thereby not harming the surrounding tissue or disturbing the residual bacteria-flora of the tissue.

Photochem Photobiol. 2009 Nov-Dec;85(6):1364-74.

Near-infrared photoinactivation of bacteria and fungi at physiologic temperatures.

Bornstein E<>, Hermans W<>, Gridley S<>, Manni J<>.

Nomir Medical Technologies, Waltham, MA, USA.

We examined a laser system (870 and 930 nm), employing wavelengths that have exhibited cellular photodamage properties in optical traps. In vitro, with 1.5 cm diameter flat-top projections (power density of 5.66 W cm(-2)), at physiologic temperatures, we achieved photoinactivation of Staphylococcus aureus, Escherichia coli, Candida albicans and Trichophyton rubrum. Using nonlethal dosimetry, we measured a decrease in trans-membrane potentials (DeltaPsimt and DeltaPsip) and an increase in reactive oxygen species (ROS) generation in methicillin-resistant S. aureus (MRSA), C. albicans and human embryonic kidney cells. We postulate that these multiplexed wavelengths cause an optically mediated mechano-transduction of cellular redox pathways, decreasing DeltaPsi and increasing ROS. The cellular energetics of prokaryotic and fungal pathogens, along with mammalian cells, are affected in a similar manner when treated with these multiplexed wavelengths at the power densities employed. Following live porcine thermal tolerance skin experiments, we then performed human pilot studies, examining photodamage to MRSA in the nose and fungi in onychomycosis. No observable damage to the nares or the nail matrix was observed, yet photodamage to the pathogens was achieved at physiologic temperatures. The selective aspect of this near-infrared photodamage presents the possibility for its future utilization in human cutaneous antimicrobial therapy.

Acta Odontol Latinoam. 2009;22(2):93-7.

In vitro lethal photosensitization of S. mutans using methylene blue and toluidine blue O as photosensitizers.

Araújo PV<>, Teixeira KI<>, Lanza LD<>, Cortes ME<>, Poletto LT<>.

Departamento de Odontologia Restauradora da Faculdade de Odontologia da Universidade Federal de Minas Gerais, Brazil.


The purpose of this in vitro study was to evaluate the antimicrobial effect of photodynamic therapy on Streptococcus mutans (A TCC 25175) suspensions, using a red laser for one minute in combination with toluidine blue O (TBO) or methylene blue (MB). Both photosensitizers were used in three concentrations (25, 10 and 5 mg/L). The activity of photosensitizers and laser irradiation were tested separately on the bacteria, as well as the irradiation of this light source in the presence of the TBO or MB. These groups were compared to a control group, in which the microorganism did not receive any treatment. The activity of both TBO and MB or laser irradiation, alone, were not able to reduce the number of S. mutans. In the groups of lethal photosensitization, a bacterial reduction of 70% for TBO and 73% for MB was observed when these photosensitizers were used at 25 mg/L and a reduction of 48% was observed for MB at 5mg/L. In other concentrations there were no significant differences in comparison to the control group. Both the TBO and the MB at 25 mg/L associated with a red laser had an excellent potential for use in PDT in lethal sensitization of S. mutans.

Photomed Laser Surg. 2007 Jun;25(3):150-8

Antiinfectives and low-level light: a new chapter in photomedicine.

Sommer AP<>.

Materials Division, University of Ulm, Ulm, Germany.

OBJECTIVE: The purpose of this study was to identify synergistic effects in the interaction of light with biosystems in the presence of chemical agents. Their systematic analysis promises therapeutic strategies.

BACKGROUND DATA: Light intensities around 1000 Wm(2) potentially induce density variations in nanoscopic water layers adhering to surfaces in air or subaquatically. In permeable nanoscopic compartments in the interior of biosystems, this could result in powerful flow processes and bidirectional flows for repetitive applications of light. Consequently, external stimulation with light will force microorganisms and cells to incorporate a suitable antiinfective. Nanoscale biosystems, which respond to both light stimulation and antibiotics, are nanobacteria. Responses include growth, inhibition, and slime secretion. Slime secretion was provoked in vitro by gentamycin, an agent proposed for in vivo eradication, and blocked by light. Depending on the field of action, co-operative effects between light and an antiinfective can be exploited by considering two properties of the drug: transmission of light and resorption by the tissue. Antiinfectives can be administered in an active form or via drug delivery systems. In the latter case, a double action of the light could be exploited: stimulated release from the carrier and subsequent uptake by the targeted biosystem.

METHODS: The attenuation of laser light (670 nm) by antiinfectives was measured in films of different thickness of a vaginal suppository. The effect of 670-nm laser light – not absorbed by water – on nanoscopic water layers was examined by comparing the evaporation time of irradiated drops of water-based nanosuspensions with non-irradiated controls.

RESULTS: The 6-microm-thick suppository films were virtually transparent to the laser light, and the 1-mm-thick films totally attenuated it. Nanosuspension drops irradiated with 670-nm light needed more time to evaporate than controls.

CONCLUSION: Low-level light (LLL) therapy is compatible with antiinfectives, and even capable of boosting effects of superficially applied and/or absorbed antiinfectives. Temporal coordination between light treatment and drug administration maximizes drug effects and minimizes possible adverse effects. Irradiation should start when the drug concentration has reached its maximum in the desired field of action. Light-induced flow in nanoscale cavities could represent one mechanism of LLL therapy.

Vopr Kurortol Fizioter Lech Fiz Kult. 2006 Sep-Oct;(5):20-3.

 Low intensity effects on local immunity of female reproductive system affected with chlamidia infection

[Article in Russian]

Gizinger OA<>, Dolgushin II<>.

Low-intensity laser impact on the main effector functions of the cervical secretion neutrophils in females suffering from Chlamidia infection has been studied. Dysfunction of neutrophil granulocytes of the cervical secretion was revealed. This manifested in the decreased number of phagocytes and lower rates of phagocytosis. The study of cervical secretion neutrophils has found that the content of active intracellular forms of oxygen was decreased in patients compared to healthy subjects. Low-intensity laser stimulated not only phagocytosis but also intracellular generation of active oxygen forms. Thus, low-intensity laser eliminates dysfunction of cervical secretion neutrophils.

Zh Mikrobiol Epidemiol Immunobiol. 2006 Jul-Aug;(4):105-9.

Immunological and microbiological aspects of low intensity laser effect on the factors of local immunity of the reproductive tract in women with chlamydia infection.

 [Article in Russian]

Dolgushin II<>, Gizinger OA<>, Telesheva LF<>.

Assessment of immunological and microbiological efficacy of Chlamydia cervicitis management was made by a complex method with a low intensity laser. The total number of leukocytes, percentage of viable cells and the number of neutrophils were detected in cervical secrets. Functional status of neutrophils was studied by a content of lysosomes on the ground of spontaneous and induced by latex HCT-reducing capacity, phagocytic activity. A system of cytokines was studied by interleukine level (IL-1 alpha, IL-1 beta, TNF-alpha, IL-8) and IFN-gamma content in cervical mucus. Positive clinical effect of the local use of the low intensity laser for Chlamydia cervicitis treatment was accompanied by positive changes in immunological indices of cervical secret, normal concentration of cytokines in cervical secret, restoration of the number and functions of neutrophils. Local use of the low intensity laser contributed to decreased number of opportunistic pathogenic microorganisms and their associations, and restored local flora.

J Photochem Photobiol B. 2006 May 1;83(2):87-93. Epub 2006 Feb 7.

Effect of low-level helium-neon laser therapy on the healing of third-degree burns in rats.

 Bayat M<>, Vasheghani MM<>, Razavi N<>.

Cell and Molecular Biology Research Center, Department of Anatomy, School of Medicine, Shaheed Beheshti University of Medical Sciences, P.O. Box 19395/4719, Tehran, Evin 1985717443, Iran.

This paper presents the results of a study on the effects of low-level helium-neon laser therapy (LL He-Ne LT) on the healing of burns. Seventy-eight adult male rats, having been subjected to third-degree burns, were randomly divided into four groups: two laser treated groups (n=20, each), one control group (n=19) and one nitrofurazone treated group (n=19). In the two laser treated groups, the burns were treated on a daily basis with LL He-Ne LT with an energy density of 1.2 and 2.4 J/cm(2), respectively. The response to treatment was assessed histologically at 7, 16 and 30 days after burning, and microbiologically at day 15. Analysis of variance showed that the mean of blood vessel sections in the 1.2J/cm(2) laser group was significantly higher than those in the other groups and the mean of the depth of new epidermis in the 2.4 J/cm(2) laser group on day 16 was significantly lower than in the nitrofurazone treated group (P=0.025, P=0.047, respectively). When Staphylococcus aureus and Pseudomonas aeruginosa grew in more than 50% of samples obtained from control group, there were no S. aureus and P. aeruginosa in the samples of 2.4 J/cm(2) laser group. It is concluded that LL He-Ne LT induced the destruction of S. aureus and P. aeruginosa in third-degree burns of rats, yet at the same time our histological findings showed that LL He-Ne LT caused a significant increase in the mean of blood vessel sections on day 7 after third degree burns and a decrease in the mean of the depth of new epidermis on day 16 after the same burns in rats.

Photomed Laser Surg. 2005 Dec;23(6):571-4.

Helium-neon and nitrogen irradiation accelerates the phagocytic activity of human monocytes.

Hemvani N<>, Chitnis DS<>, Bhagwanani NS<>.

Department of Microbiology and Immunology, Choithram Hospital & Research Centre, Indore, India.

OBJECTIVE: Intracellular survival of mycobacteria within monocytes is a crucial stage in the pathogenesis of tuberculosis. The aim was to check intracellular survival of Mycobacterium fortuitum within the human monocytes exposed to He-Ne and nitrogen laser irradiation.

BACKGROUND DATA: Tuberculosis remains one of the most important infectious diseases for developing countries. Low-level laser therapy (LLLT) has been tried to treat tubercular cavitory lung disease with encouraging results. The in vitro photobiological effect of low level laser radiation on the intracellular mycobacteria needs to be evaluated before we could go for large clinical trials.

METHODS: The aliquots of human monocytes from peripheral blood of healthy volunteers and tuberculosis cases were exposed to He-Ne or nitrogen laser beam. The non-irradiated monocytes from the same source served as controls. The monocytes were then challenged with M. fortuitum, and surviving mycobacteria within monocytes were subjected to viable counts.

RESULTS: Enhanced killing of mycobacterial cells was seen among monocytes exposed to He-Ne and nitrogen laser irradiation.

CONCLUSIONS: He-Ne and nitrogen laser irradiation activates the monocytes to increase intracellular killing of mycobacteria.

J Periodontal Res. 2003 Aug;38(4):428-35.

Lethal photosensitization of periodontal pathogens by a red-filtered Xenon lamp in vitro.

 Matevski D<>, Weersink R<>, Tenenbaum HC<>, Wilson B<>, Ellen RP<>, Lépine G<>.

Faculty of Dentistry, University of Toronto, University of Toronto, Ontario, Canada.


BACKGROUND: The ability of Helium-Neon (He-Ne) laser irradiation of a photosensitizer to induce localized phototoxic effects that kill periodontal pathogens is well documented and is termed photodynamic therapy (PDT).

OBJECTIVES: We investigated the potential of a conventional light source (red-filtered Xenon lamp) to activate toluidine blue O (TBO) in vitro and determined in vitro model parameters that may be used in future in vivo trials.

MATERIALS AND METHODS: Porphyromonas gingivalis 381 was used as the primary test bacterium.

RESULTS: Treatment with a 2.2 J/cm2 light dose and 50 micro g/ml TBO concentration resulted in a bacterial kill of 2.43 +/- 0.39 logs with the He-Ne laser control and 3.34 +/- 0.24 logs with the lamp, a near 10-fold increase (p = 0.028). Increases in light intensity produced significantly higher killing (p = 0.012) that plateaued at 25 mW/cm2. There was a linear relationship between light dose and bacterial killing (r2 = 0.916); as light dose was increased bacterial survival decreased. No such relationship was found for the drug concentrations tested. Addition of serum or blood at 50% v/v to the P. gingivalis suspension prior to irradiation diminished killing from approximately 5 logs to 3 logs at 10 J/cm2. When serum was washed off, killing returned to 5 logs for all species tested except Bacteroides forsythus (3.92 +/- 0.68 logs kill).

CONCLUSIONS: The data indicate that PDT utilizing a conventional light source is at least as effective as laser-induced treatment in vitro. Furthermore, PDT achieves significant bactericidal activity in the presence of serum and blood when used with the set parameters of 10 J/cm2, 100 mW/cm2 and 12.5 micro g/ml TBO.

J Chemother. 2003 Aug;15(4):329-34.

Comparative antistreptococcal activity of photobactericidal agents.

 O’Neill J<>, Wilson M<>, Wainwright M<>.

Department of Microbiology, Eastman Dental Institute, University College London, 256 Gray’s Inn Road, London WC1X 8LD, UK.


In order to establish a comparative order of efficacy among established photosensitising compounds currently under investigation, the in vitro photobactericidal activities of six commercially available photosensitisers were investigated at equal concentration against Streptococcus sanguis using a Helium Neon (HeNe) laser (632.8 nm). Of the photosensitisers used, the four phenothiazinium compounds were efficient photobactericidal agents as was the protoporphyrin IX salt. However, the zinc phthalocyaninetetrasulfonate was less effective. Of the active agents, 1,9-dimethyl Methylene Blue (DMMB) was notable in achieving complete bacterial kill when used at a concentration of 40.85 microM in conjunction with a light energy dose of 21.8 J cm(-2), although there was inherent dark activity associated with this compound. Since each of the photosensitisers is well known to produce singlet oxygen, the relative activities exhibited are thought to be due to differences in bacterial cell uptake, which in turn are related to the physicochemical properties of the photosensitisers, in particular, to the combination of lipophilicity and ionic character.

J Clin Laser Med Surg. 2003 Oct;21(5):283-90.  

Effects of low-level laser therapy (LLLT) of 810 nm upon in vitro growth of bacteria: relevance of irradiance and radiant exposure.

Nussbaum EL, Lilge L, Mazzulli T.

Rehabilitation Services, Mount Sinai Hospital and Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada.<>

OBJECTIVE: The aim of this study was to investigate the irradiance-dependency of low-level laser therapy (LLLT) effects on bacterial growth.

BACKGROUND: LLLT is applied to open wounds to improve healing; however, its effect on wound bacteria is not well understood.

MATERIALS AND METHODS: Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were irradiated using a wavelength of 810 nm at irradiances of 0.015 W/cm2 (0-50 J/cm2) and 0.03 W/cm2 (0-80 J/cm2). Bacteria were counted after 20 h of incubation.

RESULTS: LLLT effects varied significantly with species. P.aeruginosa growth decreased overall dependent on an interaction of irradiance and radiant exposure; greatest inhibition was produced using high irradiance delivering radiant exposures in the range of 1-20 J/cm2 (p = 0.001-0.04). In contrast, E. coli growth increased overall (p = 0.01), regardless of irradiance; greatest effects were produced using low radiant exposures (1-20 J/cm2). There was a main effect for irradiance (p = 0.03) on S. aureus growth; however, growth was not different compared with controls. Additional analysis showed that there were differences in growth of P.aeruginosa when comparing samples that were matched by exposure times (66, 329, 658, 1316, 1974, and 2632 sec) rather than radiant exposure; this suggests that irradiance rather than exposure time was the significant factor in P. aeruginosa inhibition.

CONCLUSION: These findings have immediate relevancy in the use of LLLT for infected wounds. Exposure to 810-nm irradiation (0.03 W/cm2) could potentially benefit wounds infected with P. aeruginosa. However, increased E. coli growth could further delay recovery.

J Clin Laser Med Surg. 2003 Aug;21(4):231-5.

A preliminary investigation into light-modulated replication of nanobacteria and heart disease.

Sommer AP<>, Oron U<>, Pretorius AM<>, McKay DS<>, Ciftcioglu N<>, Mester AR<>, Kajander EO<>, Whelan HT<>.

Central Institute of Biomedical Engineering, University of Ulm, 89081 Ulm, Germany.

OBJECTIVE: The purpose of this preliminary study is to evaluate the effect of various wavelengths of light on nanobacteria (NB).

BACKGROUND DATA: NB and mitochondria use light for biological processes. NB have been described as multifunctional primordial nanovesicles with the potential to utilize solar energy for replication. NB produce slime, a process common to living bacteria. Slime release is an evolutionary important stress-dependent phenomenon increasing the survival chance of individual bacteria in a colony. In the cardiovascular system, stress-induced bacterial colony formation may lead to a deposition of plaque.

METHODS: Cultured NB were irradiated with NASA-LEDs at different wavelengths of light: 670, 728 and 880 nm. Light intensities were about 500k Wm(-2), and energy density was 1 x 10(4) J m(-2).

RESULTS: Monochromatic light clearly affected replication of NB. Maximum replication was achieved at 670 nm.

CONCLUSIONS: The results indicate that suitable wavelengths of light could be instrumental in elevating the vitality level of NB, preventing the production of NB-mediated slime, and simultaneously increasing the vitality level of mitochondria. The finding could stimulate the design of cooperative therapy concepts that could reduce death caused by myocardial infarcts.

J Clin Laser Med Surg. 2002 Dec;20(6):325-33.  

Effects of 630-, 660-, and 905-nm laser irradiation delivering radiant exposure of 1-50 J/cm2 on three species of bacteria in vitro.

Nussbaum EL, Lilge L, Mazzulli T.

Rehabilitation Services, Mount Sinai Hospital and Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada.

OBJECTIVE: To examine the effects of low-intensity laser therapy (LILT) on bacterial growth in vitro.

BACKGROUND DATA: LILT is undergoing investigation as a treatment for accelerating healing of open wounds. The potential of coincident effects on wound bacteria has received little attention. Increased bacterial proliferation could further delay recovery; conversely inhibition could be beneficial.

MATERIALS AND METHODS: Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus were plated on agar and then irradiated with wavelengths of 630, 660, 810, and 905 nm (0.015 W/cm(2)) and radiant exposures of 1-50 J/cm(2). In addition, E. coli was irradiated with 810 nm at an irradiance of 0.03 W/cm(2) (1-50 J/cm(2)). Cells were counted after 20 h of incubation post LILT. Repeated measures ANOVA and Tukey adjusted post hoc tests were used for analysis.

RESULTS: There were interactions between wavelength and species (p = 0.0001) and between wavelength and radiant exposure (p = 0.007) in the overall effects on bacterial growth; therefore, individual wavelengths were analyzed. Over all types of bacteria, there were overall growth effects using 810- and 630-nm lasers, with species differences at 630 nm. Effects occurred at low radiant exposures (1-20 J/cm(2)). Overall effects were marginal using 660 nm and negative at 905 nm. Inhibition of P. aeruginosa followed irradiation using 810 nm at 5 J/cm(2) (-23%; p = 0.02). Irradiation using 630 nm at 1 J/cm(2) inhibited P. aeruginosa and E. coli (-27%). Irradiation using 810 nm (0.015 W/cm(2)) increased E. coli growth, but with increased irradiance (0.03 W/cm(2)) the growth was significant (p = 0.04), reaching 30% at 20 J/cm(2) (p = 0.01). S. aureus growth increased 27% following 905-nm irradiation at 50 J/cm(2).

CONCLUSION: LILT applied to wounds, delivering commonly used wavelengths and radiant exposures in the range of 1-20 J/cm(2), could produce changes in bacterial growth of considerable importance for wound healing. A wavelength of 630 nm appeared to be most commonly associated with bacterial inhibition. The findings of this study might be useful as a basis for selecting LILT for infected wounds.

J Appl Microbiol. 2002;92(4):618-23.

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

 Kömerik N<>, Wilson M<>.

Department of Microbiology, Eastman Dental Institute for Oral Health Care Sciences, University College London, UK.


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.

2002. 91f.

Low-intensity laser coupled with photosensitizer to reduce bacteria in root canals compared to chemical control.


Dissertation (Professional Master’s Degree “Lasers in Dentistry”) – Nuclear and Energy Research Institute / School of Dentistry, University of São Paulo, São Paulo. Advisor: Martha Simões Ribeiro, DDS, PhD, José Luiz Lage-Marques. DDS, PhD

The photodynamic therapy is a process in which a dye is associated with an appropriate wavelength of light and this dye goes to an excited state. The excited photosensitizer reacts with oxygen to form the highly reactive compound singlet oxygen, and this compound can kill bacteria and tumor cells. The purpose of this study was to evaluate the bacterial reduction in root canal contaminated with Enterococcus Faecalis. Thirty teeth with their root canals prepared were contaminated with E. faecalis. Ten teeth have received the chemical substance sodium hypochlorite for 30 minutes; ten teeth have received the azulene dye paste for 5 minutes and have been irradiated with a diode laser, output power 10mW and ?= 685nm for 3 minutes. Ten teeth have not received treatment (control group). The bacterial reduction was significantly higher for laser group when compared to chemical and control groups. These results indicate that photodynamic therapy was an effective method to kill bacteria.

Lasers Med Sci. 2001;16(4):267-75.  

The effect of He-Ne laser (632.8 nm) and Solcoseryl in vitro.

al-Watban FA, Andres BL.

Laser Medicine Section, Biological and Medical Research Department, MBC-03, King Faisal Specialist Hospital and Research Centre, PO Box 3354, 11211 Riyadh, Saudi Arabia.

He-Ne laser (632.8 nm) and Solcoseryl (SS), a non-protein calf haemodialysate, were used in the enhancement of wound healing. Nonetheless, a study on the use of He-Ne laser with SS has not been done. The purpose of this study is to determine the effect of He-Ne laser biostimulation in combination with SS on Chinese hamster ovary (CHO) and human skin fibroblast (HSF). A dose response for the cloning efficiency (CE) of CHO and HSF cells in 5% fetal bovine serum in minimum essential medium (FBS-MEM) with 6-125 micrograms/ml SS and He-Ne laser using an optimum power density of 1.25 mW/cm2 and cumulative doses (CD) of 60-600 mJ/cm2 given for three consecutive days, were done. The combined effects of He-Ne laser 180 mJ/cm2 with 6 and 12 micrograms/ml SS were determined. Quadruplicate cultures were done. Student t-test was used to determine differences of treatment groups from controls. CHO and HSF CE were increased using 180 mJ/cm2 laser by 13.1% +/- 4.5% (p < 0.0025) and 39.1% +/- 7.9% (p < 0.0005); SS 6 micrograms/ml by 14.4% +/- 8.7% (p = 0.01) and 20.7% +/- 10.9% (p = 0.01); SS 12 micrograms/ml by 17.7% +/- 6.3% (p = 0.001) and 23.9% +/- 5.6% (p < 0.0025); laser + SS 6 micrograms/ml by 15.1% +/- 8.8% (p < 0.01) and 60.9% +/- 9.4% (p < 0.0001); laser + SS 12 micrograms/ml by 23.0% +/- 1.5% (p < 0.0001) and 70.7% +/- 11.4% (p < 0.0001), respectively. Additional significant increases in CE were observed on CHO using laser + SS 12 micrograms/ml by 8.6% +/- 1.3% (p < 0.025) and on HSF using laser + SS 6 micrograms/ml and laser + SS 12 micrograms/ml by 15.6% +/- 6.8% (p < 0.025) and 22.7% +/- 10.6% (p = 0.01), respectively, when compared to the effect of 180 mJ/cm2 laser. Results suggest that further stimulation can be achieved by using He-Ne laser with SS. This could be exploited as a new treatment modality.

Urologiia. 2000 Jan-Feb;(1):11-5.

Low-intensity laser radiation in preoperative preparation of patients with benign prostatic hyperplasia

[Article in Russian]

Ne?mark AI<>, Muzalevskaia NI<>.

Low-intensity laser therapy administered in the form of intravenous blood irradiation, transrectal and transurethral prostatic irradiation and their combination as preoperative preparation and correction of immunity disturbances in patients with benign prostatic hyperplasia (BPH) were studied. The response to the treatment was evaluated by positive changes in the immune status and bacterial contamination of the urine and prostatic tissue. Conventional preoperative preparation (uroantiseptics, antibiotics and phytotherapy) fails to correct signs of T-cell immunodeficiency, depression of phagocytic activity of neutrophils, significantly reduce bacteriurea. Laser therapy as intravenous laser blood radiation acts immunomodulatorily on cellular immunity and normalized the proportion of T-helpers of the first and second order (T-suppressors) and neutrophil phagocytosis. The antibacterial effect of this technique on urinary microflora and prostatic tissue is not very high. Local laser therapy is a potent immunostimulator of T- and B-lymphocytes, increased the index of immunoregulatory cells’ proportion, activated phagocytosis of neutrophils. It has pronounced antibacterial effect against gram-negative urinary microflora and tissue of the prostate. Combined laser therapy produced the highest immunomodulating action on T-lymphocytes and immunostimulating one on B-lymphocytes, potentiated phagocytic ability of neutrophils, elevated index of the immunoregulatory cells, but was unable to correct their imbalance completely. Antibacterial effects of combined laser therapy were the highest, including the bacterial group Proteus-Providencia. Preoperative low-intensity laser therapy of BPH reduced the number of postoperative pyoinflammatory complications, hospital stay, severity of postoperative period.

Phys Ther. 1999 Sep;79(9):839-46.

Bactericidal effect of 0.95-mW helium-neon and 5-mW indium-gallium-aluminum-phosphate laser irradiation at exposure times of 30, 60, and 120 seconds on photosensitized Staphylococcus aureus and Pseudomonas aeruginosa in vitro.

 DeSimone NA<>, Christiansen C<>, Dore D<>.

Veterans Administration Medical Center, 507 Fulton St, Durham, NC 27705, USA.

Erratum in:

Phys Ther 1999 Nov;79(11):1082.


BACKGROUND AND PURPOSE: Studies have demonstrated a bactericidal effect of laser irradiation when lasers with power outputs of (6 mW are directed toward pathogenic or opportunistic bacteria previously treated with a photosensitizing agent. The purpose of this study was to determine the bactericidal capabilities of irradiation from lasers with power outputs of less than 6 mW on photosensitized microorganisms.

METHODS: Two bacteria that commonly infect skin lesions, Staphylococcus aureus and Pseudomonas aeruginosa, were used. The 2 lasers used, the 0.95-mW helium -neon laser and the 5-mW indium-gallium-aluminum-phosphate laser, emit light at a wavelength close to the absorption maxima of the sensitizing agent chosen, toluidine blue O. This agent was used because of its proven effectiveness in sensitizing bacteria. For each bacterial strain, toluidine blue O was added to a 108 cells/mL solution until a 0.01% weight/volume ratio was obtained. These mixtures were spread on agar-coated petri dishes, which were then exposed to 1 of the 2 lasers for 30, 60, and 120 seconds. The cultures were then grown overnight and examined for one or more visible zones of inhibition. The areas surrounding the irradiated zone provided a control for the effects of toluidine blue O alone. To determine the effects of laser irradiation without prior toluidine blue O sensitization, separate plates were established using unsensitized bacteria.

RESULTS: Although inconsistencies between plates were noted, both lasers produced at least one zone of inhibition in both bacterial species at all 3 time periods. The 5-mW laser, however, produced a greater number of these zones.

CONCLUSION AND DISCUSSION: Laser-induced microbial killing of photosensitized organisms could have clinical applications in the treatment of infected skin lesions, pending in vivo studies.

J Antimicrob Chemother. 1997 Dec;40(6):873-6.

Killing of methicillin-resistant Staphylococcus aureus in vitro using aluminum disulphonated phthalocyanine, a light-activated antimicrobial agent.

Griffiths MA<>, Wren BW<>, Wilson M<>.

Department of Microbiology, Eastman Dental Institute for Oral Health Care Sciences, University of London, UK.


The aim of this study was to determine whether 16 epidemic methicillin-resistant strains of Staphylococcus aureus (EMRSA) could be killed by the light-activated antimicrobial agent aluminium disulphonated phthalocyanine (AIPcS2). EMRSA suspensions were irradiated with light from a laser diode in the presence of AIPcS2 and survivors enumerated. All strains were susceptible to killing, the bactericidal effect being dependent on the AIPcS2 concentration and the light dose. AIPcS2 rendered the bacteria light-sensitive almost immediately and killing was unaffected by the growth phase of the organism. Scavengers of singlet oxygen and free radicals protected the bacteria from killing. These results imply that light-activated antimicrobial agents may be useful in eliminating EMRSA from wounds or carriage sites.

Photochem Photobiol. 1997 Jun;65(6):1026-31.

Effect of dosimetric and physiological factors on the lethal photosensitization of Porphyromonas gingivalis in vitro.

Bhatti M<>, MacRobert A<>, Meghji S<>, Henderson B<>, Wilson M<>.

Department of Microbiology, Eastman Dental Institute for Oral Health Care Sciences, University of London, UK.


The aims of this study were to (1) determine the effect of dosimetric and physiological factors on the lethal photosensitization of Porphyromonas gingivalis using toluidine blue O (TBO) and light from a helium/neon (HeNe) laser; (2) determine the influence of sensitizer concentration, preirradiation time, serum and growth phase on sensitizer uptake by P. gingivalis. The dosimetric factors studied were concentration of TBO, light dose and preirradiation time. The physiological factors were presence of serum, pH and bacterial growth phase. Sensitizer uptake by P. gingivalis under various conditions was determined using tritiated TBO (3H-TBO). In the presence of TBO, a light dose-dependent increase in kill was attained (100% kill at 4.4 J). There was no significant effect on the numbers killed when TBO was increased from 12.5 to 50 micrograms/mL. An increase in preirradiation time gave slightly increased kills. High kills were achieved at all three pH (6.8-8.0). Although kills were substantial in the presence of serum, they were significantly less than those obtained in the presence of saline. Cells in all three growth phases were susceptible to lethal photosensitization, although stationary phase cells were slightly less susceptible. Maximum uptake of TBO occurred within 60 s and uptake in serum was less than in saline. The uptake by the log phase cells was greater at lower concentrations of sensitizer (50 micrograms/mL), compared to the other two phases.

Med Microbiol. 1996 Apr;44(4):245-52.

The killing of Helicobacter pylori by low power laser light in the presence of a photosensitiser.

 Millson CE<>, Wilson M<>, Macrobert AJ<>, Bedwell J<>, Bown SG<>.

The National Medical Laser Centre, University College London Medical School, UK.


Helicobacter pylori is associated with various gastrointestinal disorders. Lethal photosensitisation was investigated as a possible technique for killing H. pylori which might offer a better alternative to antibiotics. The susceptibility of H. pylori to lethal photosensitisation was determined by mixing suspensions of H. pylori with various photosensitisers and plating out on blood agar before irradiation with low-power laser light. Five sensitisers were studied further by mixing them with H. pylori in a tissue-culture plate and counting survivors after irradiation as a function of laser exposure time, dye concentration and pre-irradiation time. Crystal violet and thionine were ineffective as sensitisers, but zones of inhibition appeared with methylene blue (MB), protoporphyrin IX (PPIX), haematoporphyrin derivative (HPD), toluidine blue O (TBO) and disulphonated aluminium phthalocyanine (S2). Laser light or sensitiser alone did not affect bacterial viability. S2 (100 microg/ml) with a laser light energy density of 16 J/cm2, HPD (10O microg/ml) with 160 J/cm2, MB (100 microg/ml) with 21 J/cm2, PPIX (150 microg/ml) with 320 J/cm2 and TBO (50 microg/ml) with 160 J/cm2 all reduced bacterial viability by >99%. The killing of sensitised H. pylori by laser light offers a new approach to the treatment of localised infections when all colonised areas are accessible to light.

J Antimicrob Chemother. 1996 Feb;37(2):377-81.

Killing of Streptococcus sanguis in biofilms using a light-activated antimicrobial agent.

 Wilson M<>, Burns T<>, Pratten J<>.

Department of Microbiology, Eastman Dental Institute of Oral Health Care Sciences, University of London, UK.


The aim of this study was to determine whether Streptococcus sanguis, when in a biofilm, could be killed using a light-activated antimicrobial agent. Biofilms were grown on hydroxyapatite, irradiated with up to 12.2 J of light from a gallium aluminium arsenide laser in the presence of aluminium disulphonated phthalocyanine (AlPcS2) and survivors enumerated. No significant decrease in the viable count was found when either the AlPcS2 or the laser light was used alone. There was a light dose related decrease in the viable counts of irradiated AlPcS2-treated biofilms. No viable streptococci were detectable following irradiation with 12.2 J of laser light.

J Photochem Photobiol B. 1996 Jan;32(1-2):59-65.

Ex-vivo treatment of gastric Helicobacter infection by photodynamic therapy.

 Millson CE<>, Wilson M<>, MacRobert AJ<>, Bown SG<>.

National Medical Laser Centre, University College London Medical School, UK.


Attempts to develop PDT for eradication of Helicobacter infection have only been successful in vitro. We have investigated the effect of topical sensitization (except ALA) of Helicobacter mustelae on explanted ferret gastric mucosa using one of five sensitizers (methylene blue (MB), toluidine blue O (TBO), phthalocyanine, haematoporphyrin derivative and 5-aminolavulinic acid), followed by irradiation with an appropriately tuned copper vapour pumped dye laser. A 90% reduction in counts of bacteria sensitized with 0.75 mg TBO kg-1 were seen after irradiation with 200 J cm-2. Concentrations of MB of 0.75 mg kg-1 and 7.5 mg kg-1 were not toxic to H. mustelae, but the further addition of 20 J cm-2 laser light reduced colony counts by more than 99%. MB at a concentration of 75 mg kg-1 exhibited significant dark toxicity towards H. mustelae, but further addition of 20 J cm-2 laser light resulted in near eradication of all colonies. The remaining three compounds were ineffective. Finally, we studied the microscopic fluorescence distribution of MB (7.5 mg kg-1) on ferret gastric mucosa after topical administration. Fluorescence was greatest in the superficial mucosal layer, upon which lies the bacteria. However, from experiments on rats, the energy required to kill the sensitized bacteria was insufficient to damage the underlying mucosa. We conclude that Helicobacter can be killed on host mucosal epithelium following topical administration of MB and subsequent exposure to laser light.

Acta Univ Palacki Olomuc Fac Med. 1996;140:43-6.

In vitro He-Ne laser effect on some immunological functions of polymorphonuclears and monocytes in rabbits.

Luza J<>, Hubácek J<>.

Department of Physiology, Medical Faculty, Palacký University, Olomouc, Czech Republic.

The aim of this study is to evaluate in vitro the effect of Helium-Neon (He-Ne) laser irradiation on the viability, adherence, phagocytic activity of the polymorphonuclears and monocytes. Also the level of metabolic processes in phagocytizing blood cells, monocytes and polymorphonuclears was estimated and evaluated by the INT-test. Evaluation of the leukocyte adherence, the method of MacGregor was used. Phagocytic activity was examined by classical method using microspherical hydrophilic particles (Hema-particles). He-Ne laser in a small dosage (< or = 0.8 J) increases the leukocyte adherence, after higher laser irradiation dosage (> 1.2 J) the leukocyte adherence is decreased. The laser effect on the phagocytic activity of both types of blood cells, polymorphonuclears and monocytes is similar. Small dosage of the laser irradiation increases the phagocytic activity, and after higher laser irradiation phagocytic activity is decreased. Also the changes of the level of metabolic processes in the phagocytizing cells are very similar with the changes of phagocytic activity. The viability of the blood cells examined after higher laser irradiation is gradually decreased.

Caries Res. 1995;29(3):192-7.

Effect of dentine and collagen on the lethal photosensitization of Streptococcus mutans.

 Burns T<>, Wilson M<>, Pearson GJ<>.

Department of Microbiology, Eastman Dental Institute for Oral and Dental Health Care Sciences, London, UK.


Suspensions of the cariogenic bacterium, Streptococcus mutans were treated with either toluidine blue O or aluminium disulphonated phthalocyanine and then exposed to light from a helium-neon or gallium-aluminium-arsenide laser, respectively, after passing through demineralized dentine slices. Bacteria were also embedded in a collagen matrix prior to sensitization and exposure to the laser light. When dentine slices were interposed between the laser light and the bacterial suspension, substantial kills (10(7) CFU) were achieved at energy doses of 876, 1,752, and 3,504 mJ with the helium-neon laser and of 1,188, 2,376, and 4,752 mJ with the gallium-aluminium-arsenide laser. There was no apparent relationship between the extent of killing and the degree of demineralization of the dentine. Prolonging the exposure of the sensitized bacteria to the laser light increased the kill achieved. Substantial numbers (10(8) to 10(10) CFU) of S. mutans were also killed when embedded in a collagen matrix and exposed to 438 and 1,314 mJ of helium-neon laser light and 594 and 1,782 mJ of light from the gallium-aluminium-arsenide laser. These results imply that lethal photosensitization may be effective at killing S. mutans in a carious lesion, even when the organism is embedded in demineralized dentine.

J Appl Bacteriol. 1995 May;78(5):569-74.

Bacteria in supragingival plaque samples can be killed by low-power laser light in the presence of a photosensitizer.

 Wilson M<>, Burns T<>, Pratten J<>, Pearson GJ<>.

Department of Microbiology, Eastman Dental Institute for Oral Health Care Sciences, University of London, UK.


The purpose of this study was to determine whether bacteria in supragingival plaque samples could be killed by low-power laser light in the presence of a suitable photosensitizer. Plaque samples were obtained from 10 volunteers, treated with either toluidine blue O (TBO) or aluminum disulphonated phthalocyanine (AlPcS2), and then exposed to light from a helium/neon (HeNe) or gallium aluminium arsenide (GaAs) laser respectively. Following irradiation, substantial reductions were achieved in the total anaerobic count as well as in the number of viable streptococci and actinomyces present in the samples. In the absence of laser light, the sensitizers themselves had little effect on the viability of the bacteria in the plaque samples. The HeNe/TBO combination appeared to be more effective than the GaAs/AlPcS2 combination, achieving log10 reductions of 2.95, 5.40 and 3.34 in the total anaerobic count, streptococci and actinomyces respectively with a light energy dose of 1.31 J. If effective in vivo, lethal photosensitization may be useful as a means of eliminating plaque bacteria from a carious lesion prior to its restoration.

J Med Microbiol. 1995 Jan;42(1):62-6.

Killing of methicillin-resistant Staphylococcus aureus by low-power laser light.

 Wilson M<>, Yianni C<>.

Department of Microbiology, Eastman Dental Institute for Oral Health Sciences, University of London.


The purpose of this study was to determine whether a methicillin-resistant strain of Staphylococcus aureus (MRSA) could be sensitised by toluidine blue O (TBO) to killing by light from a low-power helium/neon (HeNe) laser. Suspensions containing c. 10(10) cfu of MRSA were irradiated with light from a 35 mW HeNe laser (energy dose: 0.5-2.1 J) in the presence of TBO (1.6-12.5 micrograms/ml) and the survivors were enumerated. The kills attained depended on both the light energy dose and concentration of TBO employed. A 4.47 log10 reduction in the viable count was achieved with a TBO concentration of 12.5 micrograms/ml and a light dose of 2.1 J (energy density 43 J/cm2). MRSA were susceptible to killing by the laser light within 30 s of exposure to the TBO. The results of this study have demonstrated that MRSA can be rapidly sensitised by TBO to killing by HeNe laser light and that killing depends on the light energy dose and sensitiser concentration.

J Dent. 1994 Oct;22(5):273-8.

Killing of cariogenic bacteria by light from a gallium aluminum arsenide diode laser.

Burns T<>, Wilson M<>, Pearson GJ<>.

Department of Microbiology, Institute of Dental Surgery, London, UK.


Suspensions of Streptococcus mutans, S. sobrinus, Lactobacillus casei and Actinomyces viscosus were exposed to light from a gallium aluminium arsenide laser in the presence of aluminium disulphonated phthalocyanine and the numbers of survivors determined. Exposure to the laser light in the absence of the dye, or the dye in the absence of the laser light, had no significant effect on the viability of the organisms. However, a light-dose-related decrease in the viable count of all four target organisms was found on exposure to the laser light in the presence of the dye. The kills attributable to lethal photosensitization amounted to approximately 10(6) CFU in the case of each organisms. As appreciable kills were achieved within clinically convenient exposure times (30-90 s), these results imply that lethal photosensitization may be a useful technique for eliminating bacteria from carious lesions prior to restoration.

Int Dent J. 1994 Apr;44(2):181-9.

Bactericidal effect of laser light and its potential use in the treatment of plaque-related diseases.

 Wilson M<>.

Department of Microbiology, Institute of Dental Surgery, University of London, UK.


Chemical antibacterial agents are increasingly being used in prophylactic and therapeutic regimes for plaque-related diseases. As these agents can be rendered ineffective by the development of resistance in the target organisms there is a need to develop alternative antimicrobial approaches. Light from high-power lasers is known to be bactericidal and investigations have shown that it is effective against organisms implicated in caries and inflammatory periodontal diseases. However, the adverse effects of such light on dental hard tissues argue against its use solely as an antibacterial agent. Although light from low-power lasers has no adverse effect on bacterial viability, bacteria can be sensitised to killing by such light by prior treatment with a chemical photosensitising agent. Lethal photosensitisation of a wide range of cariogenic and periodontopathogenic bacteria has been demonstrated using light from a helium/neon or gallium aluminium arsenide laser in conjunction with a dye such as toluidine blue or aluminium disulphonated phthalocyanine as a photosensitiser. The advantages of the technique are that killing is achieved in very short periods of time (< 60 s), resistance development in the target bacteria would be unlikely and damage to adjacent host tissues can be avoided. This approach may be a useful alternative to antibiotics and antiseptics in eliminating cariogenic and periodontopathogenic bacteria from disease lesions.

Microbios. 1994;78(316):163-8.

Lethal photosensitisation of Staphylococcus aureus.

Wilson M<>, Pratten J<>.

Department of Microbiology, Institute of Dental Surgery, University of London, Great Britain.


The purpose of this study was to determine whether toluidine blue O (TBO) could sensitise Staphylococcus aureus to killing by light from a low-power helium/neon (HeNe) laser. Suspensions of the organism were irradiated with light from a HeNe laser in the presence and absence of TBO and the survivors enumerated. A 95% reduction (9 x 10(7) cfu) in the viable count was achieved following irradiation with 0.88 J of HeNe laser light in the presence of 12.5 micrograms/ml TBO whereas no significant reductions in viability were found when suspensions were exposed to this dose of laser light in the absence of TBO. With higher doses (3.5 J) of laser light statistically significant kills (3 x 10(7) cfu) were obtained in the absence of TBO implying the presence of an endogenous photosensitiser in the organism.

J Med Microbiol. 1993 Jun;38(6):401-5.

Sensitisation of cariogenic bacteria to killing by light from a helium-neon laser.

 Burns T<>, Wilson M<>, Pearson GJ<>.

Department of Microbiology, Institute of Dental Surgery, London.


Suspensions of the cariogenic bacteria Streptococcus mutans, S. sobrinus, Lactobacillus casei and Actinomyces viscosus were exposed to light from a 7.3-mW helium-neon laser in the presence of toluidine blue O. A substantial killing rate (c. 10(6) cfu) of all four species was achieved with a dye concentration of 50 micrograms/ml and a light energy dose of 33.6 J/cm2. This was achieved in 60 s, an exposure time that is clinically acceptable. Exposure to laser light in the absence of the dye did not significantly affect the viability of any of the organisms. This approach may be useful in dentistry to sterilise a carious lesion prior to its repair.

Oral Microbiol Immunol. 1993 Jun;8(3):182-7.

Sensitization of periodontopathogenic bacteria to killing by light from a low-power laser.

 Wilson M<>, Dobson J<>, Sarkar S<>.

Microbiology Department, Institute of Dental Surgery, London, United Kingdom.


Cultures of Porphyromonas gingivalis, Fusobacterium nucleatum and Actinobacillus actinomycetemcomitans were treated with a range of photosensitizers and then exposed to light from a 7.3 mW helium/neon laser for up to 80 s. Toluidine blue O (25 micrograms/ml) and methylene blue (25 micrograms/ml) were effective lethal photosensitizers of all 3 target organisms, enabling substantial light dose-related reductions in viable counts. Dihaematoporphyrin ester and aluminium disulphonated phthalocyanine were lethal photosensitizers only of P. gingivalis. In the absence of a photosensitizer, exposure to laser light had no significant effect on the viability of the cultures. If such low doses of light (22 J/cm2) are effective at killing bacteria in vivo, the technique may be useful as a means of eliminating periodontopathogenic bacteria from diseased sites.

J Periodontal Res. 1993 May;28(3):204-10.

Lethal photosensitization of bacteria in subgingival plaque from patients with chronic periodontitis.

 Sarkar S<>, Wilson M<>.

Department of Microbiology, Institute of Dental Surgery, London, England.


Subgingival plaque samples from patients with chronic periodontitis were exposed to light from a 7.3 mW Helium/Neon laser for 30 s in the presence and absence of 50 micrograms/ml toluidine blue O as a photosensitizer. Viable counts of various groups and species of bacteria were carried out before and after irradiation. The median numbers of viable bacteria initially present in the 30-microliters aliquots irradiated were 1.13 x 10(5) cfu (aerobes), 4.08 x 10(5) cfu (anaerobes), 4.92 x 10(3) cfu (black-pigmented anaerobes), 4.75 x 10(2) cfu (Porphyromonas gingivalis), 6.15 x 10(3) cfu (Fusobacterium nucleatum) and 1.7 x 10(4) cfu (streptococci). The dye/laser combination achieved significant reductions in the viability of these organisms, the median reductions in the viable counts being 91.1% for aerobes, 96.6% for anaerobes, 100% for black-pigmented anaerobes, P. gingivalis and F. nucleatum and 94.2% for streptococci. Overall, the viability of bacteria in the 20 plaque samples was not significantly decreased by the dye alone. However, in a small minority of samples there were indications of light-independent, dye-induced toxicity. Low-power lasers, in conjunction with appropriate photosensitizers, may be a useful adjunct to mechanical debridement in the treatment of inflammatory periodontal diseases if a similar effectiveness against subgingival plaque bacteria can be achieved in vivo.

Arch Oral Biol. 1992 Nov;37(11):883-7.

Sensitization of oral bacteria in biofilms to killing by light from a low-power laser.

 Dobson J<>, Wilson M<>.

Microbiology Laboratory, Institute of Dental Surgery, London, U.K.


Biofilms of Streptococcus sanguis, Porphyromonas gingivalis, Fusobacterium nucleatum and Actinobacillus actinomycetemcomitans were prepared on the surfaces of agar plates and a number of compounds were screened for their ability to sensitize bacteria in these biofilms to killing by light from a 7.3 mW Helium/Neon (He/Ne) laser. Toluidine blue O and methylene blue enabled detectable killing of all four target organisms after exposure to He/Ne light for 30 s. Aluminium disulphonated phthalocyanine, haematoporphyrin HCl and haematoporphyrin ester were effective photosensitizers of only some of the target organisms. These findings suggest that lethal photosensitization may be an effective means of eliminating periodontopathogenic bacteria from dental plaque.

Curr Microbiol. 1992 Aug;25(2):77-81.

Sensitization of oral bacteria to killing by low-power laser radiation.

Wilson M<>, Dobson J<>, Harvey W<>.

Microbiology Laboratory, Institute of Dental Surgery, London, UK.


Twenty-seven compounds were screened for their ability to sensitize Streptococcus sanguis to killing by light from a 7.3-mW Helium/Neon (HeNe) laser. Bacteria were mixed with various concentrations of the test compounds, spread over the surfaces of agar plates, and then exposed to light from the HeNe laser for various time periods. The plates were then incubated and examined for zones of inhibition. Those compounds found to be effective photosensitizers were then tested against Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum. Toluidine blue O, azure B chloride, and methylene blue at concentrations of 0.005% (wt/vol) were effective photosensitizers of all four species, enabling killing of bacteria following exposure to laser light for only 30 s.