Assessment of multispecies biofilm growth on root canal dentin under different radiation therapy regimens

OBJECTIVES

To assess the growth of a multispecies biofilm on root canal dentin under different radiotherapy regimens.

MATERIALS AND METHODS

Sixty-three human root dentin cylinders were distributed into six groups. In three groups, no biofilm was formed (n = 3): NoRT) non-irradiated dentin; RT55) 55 Gy; and RT70) 70 Gy. In the other three groups (n = 18), a 21-day multispecies biofilm (Enterococcus faecalis, Streptococcus mutans, and Candida albicans) was formed in the canal: NoRT + Bio) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. The biofilm was quantified (CFUs/mL). Biofilm microstructure was assessed under SEM. Microbial penetration into dentinal tubules was assessed under CLSM. For the biofilm biomass and dentin microhardness pre- and after biofilm growth assessments, 45 bovine dentin specimens were distributed into three groups (n = 15): NoRT) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm.

RESULTS

Irradiated specimens (70 Gy) had higher quantity of microorganisms than non-irradiated (p = .010). There was gradual increase in biofilm biomass from non-irradiated to 55 Gy and 70 Gy (p < .001). Irradiated specimens had greater reduction in microhardness after biofilm growth. Irradiated dentin led to the growth of a more complex and irregular biofilm. There was microbial penetration into the dentinal tubules, regardless of the radiation regimen.

CONCLUSION

Radiotherapy increased the number of microorganisms and biofilm biomass and reduced dentin microhardness. Microbial penetration into dentinal tubules was noticeable.

CLINICAL RELEVANCE

Cumulative and potentially irreversible side effects of radiotherapy affect biofilm growth on root dentin. These changes could compromise the success of endodontic treatment in oncological patients undergoing head and neck radiotherapy.

Photodynamic Therapy With Resveratrol and an Nd:YAG Laser for Enterococcus faecalis Elimination

BACKGROUND/AIM

Enterococcus faecalis is the leading cause of endodontic treatment failures. Despite various conventional disinfection approaches, microorganisms often persist in root canals. Photodynamic therapy (PDT) is an adjunct antimicrobial strategy employing a nontoxic photosensitizer (PS) and light source. This study evaluated the antimicrobial effect of PDT using an Nd:YAG laser and resveratrol (RSV) with or without pigment, and confirmed that RSV is nontoxic as a PS.

MATERIALS AND METHODS

We employed laser irradiation at a 3W output power, using RSV and red pigment as the PS, on an E. faecalis bacterial solution. Subsequently, colony-forming units were quantified. The impact of RSV on osteoblasts was measured using an MTT assay.

RESULTS

E. faecalis counts declined after laser irradiation. The combined application of laser irradiation with RSV, red pigment, or both showed a reduction compared to no irradiation and control groups without RSV and red pigment. The 50% cytotoxic concentration against osteoblast cells from mice incubated with RSV for 48 h was 162 μM. The value with RSV and laser was 201 μM and that with RSV and red pigment was 199 μM. The value with RSV, laser and red pigment was 357 μM.

CONCLUSION

The combination of Nd:YAG laser irradiation and RSV as the PS with pigment was efficacious for E. faecalis elimination without inducing any toxic effects on osteoblasts. This combination holds potential as a root canal irrigation strategy.

An in vitro study on the efficacy of hydrogen peroxide mediated high-power photodynamic therapy affecting Enterococcus faecalis biofilm formation and dispersal

OBJECTIVE

Biofilms are involved in failure of root canal treatment due to their high resistance to antimicrobial agents, which make their removal as a big challenge. The present study aims at utilizing hydrogen peroxide (HP) plus high frequency laser reinforced antimicrobial photodynamic therapy (a-PDT) as a complementary therapy against Enterococcus faecalis (E. faecalis) at planktonic and biofilm stages.

MATERIALS AND METHODS

E. faecalis at planktonic and biofilm stages was treated with the photosensitizer HP, followed by no irradiation or irradiation with a power of 2.5 W (ʎ = 980 nm). The cell viability, anti-biofilm, anti-metabolic potential, and temperature changes were evaluated.

RESULTS

The combination of HP and 980 nm diode laser intensely boosted antibacterial and anti-biofilm efficacy compared with either component alone, affirming HP reinforcement as a bacteriostatic agent. The maximum effect on biofilm occurs in 5.25% sodium hypochlorite (NaOCl) group. During laser irradiations, the mean of temperature changes remains below 5.6 °C.

CONCLUSIONS

It could be concluded that the HP could improve anti-biofilm efficacy as a photosensitizer in a-PDT.

Enhanced disinfection of E. faecalis and levofloxacin antibiotic degradation using tridoped B-Ce-Ag TiO2 photocatalysts synthesized by ecofriendly citrate EDTA complexing method

Since its use for photochemical water splitting reported first in 1972, TiO₂ is one of the most extensively studied photocatalysts for a diverse range of applications. Monodoping or codoping of the catalyst is a proven strategy to enhance the functionality of TiO₂ under solar or visible light. However, the use of three or more dopants in the development of more efficient and visible light active photocatalysts has not been investigated widely, especially for microbial disinfection. Boron/cerium/silver tridoped TiO₂ photocatalysts with curated amounts of the dopants (B = 1, 2 at.%, Ce = 0.1 at.%, Ag = 0.06 at.%), synthesized by the ecofriendly EDTA-citrate method, were evaluated for the disinfection of water using Enterococcus faecalis under UV-A irradiation and degradation of levofloxacin antibiotic under solar light. The catalyst characterization revealed that the spherical nanoparticles had a crystallite size of ~ 13 nm and bandgap energy values of 2.8-2.9 eV. 2B-0.1Ce-0.06Ag-TiO₂ is the best catalyst for microbial disinfection with a log reduction and kinetic rate constant ~ 30 and ~ 4.5 times higher than those values determined for the other codoped or monodoped catalysts, confirming an enhanced performance. Regarding levofloxacin degradation, the best performing catalyst is 1B-0.1Ce-0.06Ag-TiO₂ with degradation of 99% and 83% COD reduction in 100 min. The tridoped photocatalysts are very effective in the inactivation of Enterococcus faecalis, thus solving the problem of antimicrobial resistance in waters containing antibiotic residues.

Hybrid UV-C/microfiltration process in membrane photoreactor for wastewater disinfection

A novel hybrid UV-C/microfiltration process for water disinfection is presented, and its application in continuous mode operation to the removal of different pathogen germs (Escherichia coli, Enterococcus faecalis, and Candida albicans) present in urban wastewater. The membrane photoreactor is based on porous stainless steel membranes coated with a TiO₂ layer and illuminated by a UV-C lamp (254 nm). A valve actuator in the outlet of the UV-C stream allows operation of the system under conditions of constant transmembrane pressure (TMP) keeping the UV-C contact time in few seconds, significantly lower than the typical irradiation time employed in TiO₂ photocatalytic processes. An E. coli removal of up to 4-log in the permeate stream and up to 2-log in the UV-C outlet was achieved with a 0.2 μm membrane operating with a TMP of 0.5 bar and a UV-C contact time as low as 8 s. The microbial balance data from the cells recovered from the membrane confirmed that 96-98% of the removed microorganisms died due to the UV-C action over the membrane surface. Modification of the membrane with a TiO₂ layer has been also shown to be a suitable way to improve both the UV-C inactivation and the filtration efficiency. The results reported in this work constitute a proof of concept of the synergy between UV-C and filtration that can be achieved in a hybrid UV-C/microfiltration system, being a good example of process intensification where two products of different quality can be simultaneously obtained.

Triphenylphosphonium cation: A valuable functional group for antimicrobial photodynamic therapy

Light-mediated killing of pathogens by cationic photosensitisers is a promising antimicrobial approach that avoids the development of resistance inherent to the use of antimicrobials. In this study, we demonstrate that modification of different photosensitisers with the triphenylphosphonium cation yields derivatives with excellent photoantimicrobial activity against Gram-positive bacteria (ie, Staphylococcus aureus and Enterococcus faecalis). Thus, the triphenylphosphonium functional group should be considered for the development of photoantimicrobials for the selective killing of Gram-positive bacteria in the presence of Gram-negative species.

Antimicrobial Potential of Laser Diode in Infected Dentin

AIM

To evaluate the antibacterial effect of diode laser, associated or not with 2.5% sodium hypochlorite (NaOCl), against Enterococcus faecalis.

MATERIALS AND METHODS

Eighty dentin blocks were obtained from single-rooted human teeth and sterilized. Seventy were inoculated with 0.01 mL of fresh bacterial inoculum (within 24 hours of preparation from pure culture) standardized to 1 McFarland turbidity. Contaminated blocks were incubated for 7 days at 37°C in humid conditions. Ten uncontaminated samples were incubated at 37°C during the contamination period to serve as a negative control group, while 10 of the infected specimens served as a positive control group. The dentin blocks were randomly divided into eight experimental groups (n = 10 each) according to the method of decontamination: 2.5% NaOCl alone; 2.5% NaOCl + photodynamic therapy (PDT) with methylene blue/660 nm laser at 18 J for 180 seconds; 2.5% NaOCl + PDT with methylene blue/660 nm laser at 8 J for 80 seconds; methylene blue alone; PDT alone with methylene blue/660 nm laser at 18 J for 180 seconds; PDT alone with methylene blue/660 nm laser at 8 J laser for 80 seconds; positive control group; and negative control group. Microbial growth was evaluated by culture medium turbidity and microbial concentration was analyzed by UV spectrophotometry (adjusted to read at wavelength l = 600 nM).

RESULTS

Root canals treated with laser alone at 18 J for 180 seconds had higher bacterial contamination compared with groups in which NaOCl was used, with or without laser irradiation at 18 J for 180 seconds (p < 0.05).

CONCLUSION

Photodynamic therapy with a 660 nm diode laser effectively reduced E. faecalis contamination. These findings can guide development of further studies in search of better alternatives for endodontic treatment.

CLINICAL RELEVANCE

Chemical and mechanical root canal preparation plays an essential role in reducing microbial burden. However, microorganisms present in areas not mechanically reachable by endodontic instruments. As an alternative to fix this problem, the laser can be applied.

A Comparison of Er:YAG Laser with Photon-Initiated Photoacoustic Streaming, Nd:YAG Laser, and Conventional Irrigation on the Eradication of Root Dentinal Tubule Infection by Enterococcus faecalis Biofilms: A Scanning Electron Microscopy Study

This study evaluated the antimicrobial efficacy of Er:YAG laser activation with photon-initiated photoacoustic streaming (PIPS), Nd:YAG laser disinfection, and conventional irrigation on Enterococcus faecalis biofilms using scanning electron microscopy (SEM). Biofilms were grown on 110 root halves and divided into the following: Groups 1 and 2 (saline and 1% NaOCl with apical position of PIPS, resp.), Groups 3 and 4 (saline and 1% NaOCl with coronal position of PIPS, resp.), Groups 5 and 6 (Nd:YAG laser after saline and 1% NaOCl irrigation, resp.) and Groups 7, 8, and 9 (conventional irrigation with 1% NaOCl, 6% NaOCl, and saline, resp.). SEM images of the apical, middle, and coronal levels were examined using a scoring system. Score differences between Groups 1 and 2 were insignificant at all levels in the remaining biofilm. Group 4 had significantly greater bacterial elimination than Group 3 at all levels. Differences in Nd:YAG laser irradiation between Groups 5 and 6 were insignificant. Groups 7 and 8 were insignificantly different, except at the middle level. Saline group had a higher percentage of biofilms than the others. In this study, PIPS activation with NaOCl eliminates more E. faecalis biofilms in all root canals regardless of the position of the fiber tip.

Properties of halogenated and sulfonated porphyrins relevant for the selection of photosensitizers in anticancer and antimicrobial therapies

The impact of substituents on the photochemical and biological properties of tetraphenylporphyrin-based photosensitizers for photodynamic therapy of cancer (PDT) as well as photodynamic inactivation of microorganisms (PDI) was examined. Spectroscopic and physicochemical properties were related with therapeutic efficacy in PDT of cancer and PDI of microbial cells in vitro. Less polar halogenated, sulfonamide porphyrins were most readily taken up by cells compared to hydrophilic and anionic porphyrins. The uptake and PDT of a hydrophilic porphyrin was significantly enhanced with incorporation in polymeric micelles (Pluronic L121). Photodynamic inactivation studies were performed against Gram-positive (S. aureus, E. faecalis), Gram-negative bacteria (E. coli, P. aeruginosa, S. marcescens) and fungal yeast (C. albicans). We observed a 6 logs reduction of S. aureus after irradiation (10 J/cm²) in the presence of 20 μM of hydrophilic porphyrin, but this was not improved with incorporation in Pluronic L121. A 2–3 logs reduction was obtained for E. coli using similar doses, and a decrease of 3–4 logs was achieved for C. albicans. Rational substitution of tetraphenylporphyrins improves their photodynamic properties and informs on strategies to obtain photosensitizers for efficient PDT and PDI. However, the design of the photosensitizers must be accompanied by the development of tailored drug formulations.

Ultraviolet-C light as a means of disinfecting anesthesia workstations

BACKGROUND

Anesthesia workstations (AWs) are a reservoir for pathogenic organisms potentially associated with surgical site infections. This study examined the effectiveness of the Tru-D SmartUVC device (Tru-D LLC, Nashville, TN) on bioburden reduction (BR) on AWs.

METHODS

Strips of tissue inoculated with a known concentration of either Staphylococcus aureus, Enterococcus faecalis, or Acinetobacter sp were placed on 22 high-touch surfaces of an AW. Half of the AW surfaces received direct ultraviolet (UV) light exposure and half received indirect exposure. Two inoculated strips, in sterile tubes outside of the room, represented the control. Trials were conducted on AWs in an operating room and a small room. Strips were placed in a saline solution, vortexed, and plated on blood agar to assess BR by the number of colony forming units.

RESULTS

All experimental trials, compared with controls, exhibited a BR >99%. There was a significantly greater reduction of E faecalis colony forming units in the operating room AW under direct exposure (P = .019) compared with indirect exposure. There was no significant difference in reduction when comparing AWs between rooms.

CONCLUSION

Regardless of room size and exposure type, automated UV-C treatment greatly influences BR on AW high-touch surfaces. Hospitals instituting an automated UV-C system as an infection prevention adjunct should consider utilizing it in operating rooms for BR as part of a horizontal infection prevention surgical site infection-reduction strategy.

Determining the optimal dose of 1940-nm thulium fiber laser for assisting the endodontic treatment

Insufficient cleaning, the complex anatomy of the root canal system, inaccessible accessory canals, and inadequate penetration of irrigants through dentinal tubules minimizes the success of the conventional endodontic treatment. Laser-assisted endodontic treatment enhances the quality of conventional treatment, but each laser wavelength has its own its own limitations. The optimal parameters for the antibacterial efficiency of a new wavelength, 1940-nm Thulium Fiber Laser, were firstly investigated in this study. This paper comprises of two preliminary analyses and one main experimental study, presents data about thermal effects of 1940-nm laser application on root canal tissue, effective sterilization parameters for bacteria, Enterococcus faecalis, and finally the antibacterial effectiveness of this 1940-nm Thulium Fiber Laser irradiation in single root canal. Based on these results, the optimal parameter range for safe laser-assisted root canal treatment was investigated in the main experiments. Comparing the antibacterial effects of four laser powers on an E. faecalis bacteria culture in vitro in 96-well plates showed that the most effective group was the one irradiated with 1 W of laser power (antibacterial effect corresponding to a log kill of 3). After the optimal laser power was determined, varying irradiation durations (15, 30, and 60 s) were compared in disinfecting E. faecalis. Laser application caused significant reduction in colony-forming unit values (CFU) compared with control samples in the 17% ethylenediaminetetraacetic acid (EDTA) group. The results of bacteria counts showed that 1 W with 30 s of irradiation with a 1940-nm thulium fiber laser was the optimal dose for safely achieving maximal bactericidal effect.

[Bactericidal effects and smear layer removal of Er:YAG-laser radiation against Enterococcus faecalis in root canals]

To evaluate the cleaning ability of Er:YAG laser against Enterococcus faecalis in root canals.
 Methods: The single-rooted human teeth were sterilized and inoculated with Enterococcus faecalis and were randomly assigned into 2 groups. A group of teeth was irrigated with saline during root canal preparation while another group with NaClO. After mechanical preparation, the two groups were randomly divided into 3 subgroups according to the different treatments: Samples, laser radiation, and calcium hydroxide intracanal medication for 7 days. Bactericical effects were compared among groups. Root canal walls and dental tubules were observed under scanning electron microscope.
 Results: Er:YAG laser was the most efficient way for anti-bacteria among the groups (P<0.05), but there was no significant difference between the 2 laser groups (P>0.05). Meanwhile the smear laser was efficiently removed by laser compared with other treatments, and the laser could open the dentinal tubules.
 Conclusion: Er:YAG laser can be effectively used for root canal disinfection without NaClO and Ca(OH)2.

Comparison of Riboflavin and Toluidine Blue O as Photosensitizers for Photoactivated Disinfection on Endodontic and Periodontal Pathogens In Vitro

Photoactivated disinfection has a strong local antimicrobial effect. In the field of dentistry it is an emerging adjunct to mechanical debridement during endodontic and periodontal treatment. In the present study, we investigate the effect of photoactivated disinfection using riboflavin as a photosensitizer and blue LED light for activation, and compare it to photoactivated disinfection with the widely used combination of toluidine blue O and red light. Riboflavin is highly biocompatible and can be activated with LED lamps at hand in the dental office. To date, no reports are available on the antimicrobial effect of photoactivated disinfection using riboflavin/blue light on oral microorganisms. Planktonic cultures of eight organisms frequently isolated from periodontal and/or endodontic lesions (Aggregatibacter actinomycetemcomitans, Candida albicans, Enterococcus faecalis, Escherischia coli, Lactobacillus paracasei, Porphyromonas gingivalis, Prevotella intermedia and Propionibacterium acnes) were subjected to photoactivated disinfection with riboflavin/blue light and toluidine blue O/red light, and survival rates were determined by CFU counts. Within the limited irradiation time of one minute, photoactivated disinfection with riboflavin/blue light only resulted in minor reductions in CFU counts, whereas full kills were achieved for all organisms when using toluidine blue O/red light. The black pigmented anaerobes P. gingivalis and P. intermedia were eradicated completely by riboflavin/blue light, but also by blue light treatment alone, suggesting that endogenous chromophores acted as photosensitizers in these bacteria. On the basis of our results, riboflavin cannot be recommended as a photosensitizer used for photoactivated disinfection of periodontal or endodontic infections.

Influence of formulation on photoinactivation of bacteria by lumichrome

Lumichrome, a photodegradation product of riboflavin, is an endogenous compound in humans. The compound is more photostable and a more efficient photogenerator of singlet oxygen than riboflavin. It absorbs radiation in the UVA and blue-light region, which can be an advantage in antibacterial photodynamic therapy (aPDT) of superficial infections. The aim of this study was to investigate the in vitro aPDT effect of various lumichrome pharmaceutical formulations. Solutions of lumichrome (10(-5) - 10(-3)M) were prepared in plain phosphate buffered saline (PBS) or in PBS solutions containing cyclodextrins, DMSO, PEG 400 or polyoxamers (Pluronic). Supersaturated solutions of lumichrome in PBS were prepared via the cosolvent and solvent evaporation method. Phototoxic effects of selected lumichrome preparations were studied in planktonic Gram-positive (E. faecalis) and Gram-negative (E. coli) bacteria models. The UVA/blue light source emitted mainly in the range 340-440 nm. Lumichrome was up to tenfold more phototoxic against Gram-positive than to Gram-negative bacteria. Bacterial eradication was induced after exposure of lumichrome formulations (PBS, PEG 400 and HPγCD) combined with 24J/cm2 UVA/blue light. Increasing the concentration of lumichrome did not enhance the phototoxic effect, probably due to radiation attenuation in the highly absorbing solution (inner filter effect). Cyclodextrins were efficient enhancers of the lumichrome solubility in aqueous solutions, but inhibited the phototoxic effect. The study demonstrates that assuming the use of an optimized formulation, lumichrome has potential as a UVA/blue light photosensitizer in aPDT.

Gold nanoshell-decorated silicone surfaces for the near-infrared (NIR) photothermal destruction of the pathogenic bacterium E. faecalis

Catheter-related infections (CRIs) are associated with the formation of pathogenic biofilms on the surfaces of silicone catheters, which are ubiquitous in medicine. These biofilms provide protection against antimicrobial agents and facilitate the development of bacterial resistance to antibiotics. The application of photothermal agents on catheter surfaces is an innovative approach to overcoming biofilm-generated CRIs. Gold nanoshells (AuNSs) represent a promising photothermal tool, because they can be used to generate heat upon exposure to near-infrared (NIR) radiation, are biologically inert at physiological temperatures, and can be engineered for the photothermal ablation of cells and tissue. In this study, AuNSs functionalized with carboxylate-terminated organosulfur ligands were attached to model catheter surfaces and tested for their effectiveness at killing adhered Enterococcus faecalis (E. faecalis) bacteria. The morphology of the AuNSs was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while the elemental composition was characterized by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Furthermore, optical and photothermal properties were acquired by ultraviolet-visible (UV-vis) spectroscopy and thermographic imaging with an infrared camera, respectively. Bacterial survival studies on AuNS-modified surfaces irradiated with and without NIR light were evaluated using a colony-formation assay. These studies demonstrated that AuNS-modified surfaces, when illuminated with NIR light, can effectively kill E. faecalis on silicone surfaces.

[Photoreactivation of Escherichia coli and Enterococcus faecalis in the secondary effluent disinfected by UV-TiO2]

Effects of photoreactivating light intensity (0-41 microW x cm(-2)) on photoreactivation of Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) in the secondary effluent after UV and UV-TiO2 disinfection were investigated. The results indicated that the disinfection efficiency of UV-TiO2 was much higher than that of UV disinfection. The photoreactivation rate of E. coli was much higher in UV disinfection than that in UV-TiO2 disinfection. Under high light intensity in UV-TiO2 disinfection, high resurrection rate can be induced. However, a higher resurrection rate can be introduced even under low light intensity in the UV disinfection. Meanwhile, UV-TiO2 disinfection had a strong inhibition effect on E. faecalis photoreactivation, when the light intensity was lower than 21 microW x cm(-2), three was no resurrection occurred on E. faecalis after 72 h resurrection irradiation, only under a strong photoreactivating light intensity, the resurrection rate of E. faecalis was observed.

Sunlight mediated inactivation mechanisms of Enterococcus faecalis and Escherichia coli in clear water versus waste stabilization pond water

Escherichia coli and enterococci have been previously reported to differ in the mechanisms and conditions that affect their sunlight-mediated inactivation in waste stabilization ponds. This study was undertaken to further characterize these mechanisms, using simulated sunlight and single strains of laboratory-grown E. coli and Enterococcus faecalis, with a focus on characterizing the contribution of exogenous reactive oxygen species to the inactivation process. We found that direct damage by UVB light (280-320 nm) was not a significant inactivation mechanism for either organism. E. coli inactivation was strongly dependent on dissolved oxygen concentrations and the presence of UVB wavelengths but E. coli were not susceptible to inactivation by exogenous sensitizers present in waste stabilization pond water. In contrast, E. faecalis inactivation in pond water occurred primarily through exogenous mechanisms, with strong evidence that singlet oxygen is an important transient reactive species. The exogenous mechanism could utilize wavelengths into the visible spectrum and sensitizers were mainly colloidal, distributed between 0.2 and ∼1 μm in size. Singlet oxygen is likely an important endogenous species in both E. faecalis and E. coli inactivation due to sunlight. Although the two organisms had similar inactivation rates in buffered, clear water, the inactivation rate of E. faecalis was 7 times greater than that of E. coli in air-saturated pond water at circumneutral pH due to its susceptibility to exogenous sensitizers and longer wavelengths.

Inactivation of airborne Enterococcus faecalis and infectious bursal disease virus using a pilot-scale ultraviolet photocatalytic oxidation scrubber

High microbial concentrations and emissions associated with livestock houses raise health and environmental concerns. A pilot-scale ultraviolet photocatalytic oxidation (UV-PCO) scrubber was tested for its efficacy to inactivate aerosolized Enterococcus faecalis and infectious bursal disease virus (IBDV). Microbial reduction was determined by the difference in microbial concentrations measured in the upstream and downstream isolators that were connected to the two ends of the UV-PCO scrubber. Two UV irradiance levels were tested by using one or two UV lamps. The theoretical average UV irradiances were 6,595 microW cm(-2) with one UV lamp and 12,799 microW cm(-2) with two UV lamps. At the tested ventilation rate (70 m3 hr(-1)), the contact time was 1 sec. Reduction rate and other two indexes (k-value and Z-value) that normalized UV radiation were calculated to describe the extent of microbial inactivation. The UV-PCO scrubber eliminated > 99.7% of airborne E. faecalisfrom the incoming airstream under one UV lamp irradiance, and the reduction was further increased by 0.2-0.3% when the second UV lamp was added. The reduction rate for airborne IBDV was 72.4% with one UV lamp. The calculated k-values were 0.501-0.594 cm2 mJ(-1) for airborne E. faecalis and 0.217 cm2 mJ(-1) for IBDV The Z-value of airborne E. faecalis to UV irradiance was 9.3 (+/- 1.6) x 10(-4) cm2 microW(-1) sec(-1). The results indicate that a UV-PCO scrubber can serve as an effective and efficient technology for inactivating airborne bacteria and virus. Scaling up of the pilot-scale scrubber for field use will require considerations such as design air treatment capacity, UV irradiance level, contact time, dust concentration, susceptibility of target microorganisms, and expected reduction rate.

IMPLICATIONS

This work demonstrated that a UV-PCO scrubber can be used to inactivate animal-associated airborne microorganisms, thus reducing microbial emissions from livestock houses and minimizing the biological impact to ambient environment. The microbial reduction efficiency by the UV-PCO scrubber varied depended on the level of UV irradiation and the target microbial species. The tested viral species (infectious bursal disease virus) was more resistant to the UV-PCO scrubber as compared to its counterpart bacterial species (E. faecalis).

Effect of high-intensity focused ultrasound on Enterococcus faecalis planktonic suspensions and biofilms

In this study, the effect of high-intensity focused ultrasound (HIFU) on Enterococcus faecalis on both planktonic suspensions and biofilms was investigated. E. faecalis persist in secondary dental infections as biofilms. Glass-bottom Petri dishes with biofilms were centered at the focal point of the HIFU wave generated by a 250-kHz transducer. Specimens were subjected to HIFU exposure at different periods of 30, 60 and 120 s. The viable bacteria, removal effect and bacterial viability of biofilms attached to the Petri dish surface were studied by colony-forming units (CFUs), scanning electron microscopy and confocal microscopy, respectively. The removal and bactericidal effects of HIFU are dependent on the exposure time. A significant reduction in biofilm thickness and CFU was found with the increase in HIFU exposure. The removal or bactericidal effect of HIFU was more significant starting from 60 s of exposure. This study highlighted the potential application of HIFU as a novel method for root canal disinfection.

Removal of faecal indicator pathogens from waters and wastewaters by photoelectrocatalytic oxidation on TiO(2)/Ti films under simulated solar radiation

PURPOSE

The disinfection efficiency of water and secondary treated wastewater by means of photoelectrocatalytic oxidation (PEC) using reference strains of Enterococcus faecalis and Escherichia coli as faecal indicators was evaluated. Operating parameters such as applied potential (2-10 V), initial bacterial concentration (10(3)-10(7) CFU/mL), treatment time (up to 90 min) and aqueous matrix (pure water and treated effluent) were assessed concerning their impact on disinfection.

METHODS

PEC experiments were carried out using a TiO(2)/Ti film anode and a zirconium cathode in the presence of simulated solar radiation. Bacterial inactivation was monitored by the culture method and real-time SYBR green PCR.

RESULTS

A 6.2 log reduction in E. faecalis population was achieved after 15 min of PEC treatment in water at 10 V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to only about 4.3 log reduction, whilst negligible inactivation was recorded when the respective electrochemical oxidation process was applied (i.e. without radiation). PEC efficiency was generally improved increasing the applied potential and decreasing initial bacterial concentration. Regarding real wastewater, E. coli was more susceptible than E. faecalis during treatment at a potential of 5 V. Wastewater disinfection was affected by its complex composition and the contained mixed bacterial populations, yielding lower inactivation rates compared to water treatment. Screening the results obtained from both applied techniques (culture method and real-time PCR), there was a discrepancy regarding the recorded time periods of total bacterial inactivation, with qPCR revealing longer periods for complete bacterial reduction.

CONCLUSIONS

PEC is superior to PC in terms of E. faecalis inactivation presumably due to a more efficient separation and utilization of the photogenerated charge carriers, and it is mainly affected by the applied potential, initial bacterial concentration and the aqueous matrix.

Effect of freezing on photoreactivation of Escherichia coli and Enterococcus faecalis

The effect of freezing on photoreactivation of two strains of Escherichia coli (ATCC strain 25922 and O157:H7 strain 961019) and two strains of Enterococcus faecalis (strain ATCC 51299, vancomycin-resistant and strain ATCC 29212, vancomycin-sensitive) following ultraviolet irradiation were examined. The level of log photoreactivation of the freezing treated test organisms (frozen at -7, -15, or -30 degrees C then thawed at room temperature prior to ultraviolet irradiation) was compared with that of the samples that had not been frozen. Freezing had obvious impact on the response of the test organisms to visible light following ultraviolet irradiation. Significantly lower levels of photoreactivation were observed in the freezing treated cells. The effect of freezing on the ability of the test microbes to photoreactivate seems to be strain and species dependent. Overall, the experimental results suggest that less photoreactivation could be expected if freezing is used as a treatment method prior to ultraviolet disinfection.

Functional cationic nanomagnet-porphyrin hybrids for the photoinactivation of microorganisms

Cationic nanomagnet-porphyrin hybrids were synthesized and their photodynamic therapy capabilities were investigated against the Gram (-) Escherichia coli bacteria, the Gram (+) Enterococcus faecalis bacteria and T4-like phage. The synthesis, structural characterization, photophysical properties, and antimicrobial activity of these new materials are discussed. The results show that these new multicharged nanomagnet-porphyrin hybrids are very stable in water and highly effective in the photoinactivation of bacteria and phages. Their remarkable antimicrobial activity, associated with their easy recovery, just by applying a magnetic field, makes these materials novel photosensitizers for water or wastewater disinfection.

[The antibacterial efficacy of KaVo KEY laser on Enterococcus faecalis within infected root canals and roots surface in vitro]

OBJECTIVE

To evaluate the antibacterial efficacy of KaVo KEY laser on Enterococcus faecalis (E. faecalis) within infected root canals and roots surface in vitro.

METHODS

Fifty single-rooted teeth were selected, and infected root canals and roots surface vitro models were prepared. Then, these specimens were divided into three groups. First group were untreated as blank control. The other two groups were the laser groups: Irradiated 15 s and 30 s respectively with 80 mJ and 140 mJ in root canals and on roots surface. Microbiological samples were collected from root canals and roots surface at two time points (before irrigation and immediately after irrigation). The dentin chips from three different zone of part of root canals in each group were immediately collected and were cultured for 24 h in brain heart infusion (BHI).

RESULTS

The number of E. faecalis in root canal and root surface in each of the groups were effectively reduced (P < 0.05), and there was no significant difference between each two groups (P > 0.05). Compared with the blank control, the bacterial number in 100 microm of dental tubules decreased after specimens treated with 80 mJ, and the experimental group irradiated 15 s was a significant decease (P < 0.05). The other groups were no changed in different zone of dental tubules.

CONCLUSION

KaVo KEY laser is effective on sterilizing infected root canals and roots surface. It has also significant effect on bacterial in superficial dental tubules with low energy and short time.

Photokilling of bacteria by curcumin in selected polyethylene glycol 400 (PEG 400) preparations. Studies on curcumin and curcuminoids, XLI

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a yellow-orange pigment which can be synthesised chemically or isolated from the plant Curcuma longa L. Curcumin has a rather broad absorption peak in the range 300-500 nm (maximum approximately 430 nm) and has potential as a photosensitiser for treatment of localised superficial infections in e.g., the mouth or skin. Previously, we have demonstrated phototoxic effects of curcumin in selected aqueous preparations against both gram-positive Enterococcus faecalis and Streptococcus intermedius and gram-negative Escherichia coil bacteria in vitro. One of the most efficient preparations was curcumin in polyethylene glycol (PEG 400) dissolved in phosphate buffered saline (PBS), pH 6.1. In this study the solubilising effect of PEG 400 on curcumin molecules and the in vitro phototoxic effects of these preparations were further evaluated. The effect of varying the curcumin concentration (2.50 microM -25.00 microM), the radiant exposure (0.5-30 J/cm2) and the physical state of curcumin against the survival of E. coli was investigated. PEG 400 showed an increasing physically stabilising effect towards crystallisation of curcumin in aqueous preparation with increasing concentrations (2.5%-10.0% v/v). Despite a higher solubility of curcumin with increasing PEG 400 concentrations, the surfactant reduced the phototoxicity of curcumin against E. coil. The highest phototoxic effect was obtained when curcumin was present in the least physically stable preparation, a stock solution in ethanol added to PBS with or without the lowest test concentration of PEG 400 (2.5% v/v). The obtained phototoxic effect can be increased by increasing the irradiation dose or by choosing an optimal curcumin concentration. E. faecalis was efficiently killed by the lowest concentration of curcumin in combination with the lowest radiant exposure when curcumin was dissolved in certain PEG solutions (< 0.02% survival), but showed no reduction when exposed to preirradiated curcumin.

Photocatalytic inactivation of E. faecalis in secondary wastewater plant effluents

Photocatalytic inactivation of Enterococcus faecalis using TiO(2) suspensions was investigated and compared to the inactivation of the most commonly used faecal indicator strain Escherichia coli. In contrast to the inactivation in pure deionized water, disinfection of effluents from the biological process of an urban wastewater plant showed a longer initial lag phase and higher survival fractions after several hours of irradiation. Moreover, the fluctuation of the composition of the effluents strongly affects the overall inactivation rate, not directly related to changes in the values of organic matter content. Additionally, it was found that E. faecalis seems to be more resistant than E.coli towards the photocatalytic treatment. These results could be related to the differences in the cell wall structure of both microorganisms. The main conclusion of this work is that attention must be paid when transferring results obtained for model organism to real bacteria consortia and from laboratory experiments with deionized water to effluents from sewage plants.

On the factors influencing the performance of solar reactors for water disinfection with photosensitized singlet oxygen

Two solar reactors based on compound parabolic collectors (CPCs) were optimized for water disinfection by photosensitized singlet oxygen (1O2) production in the heterogeneous phase. Sensitizing materials containing Ru(II) complexes immobilized on porous silicone were produced, photochemically characterized, and successfully tested for the inactivation of up to 10(4) CFU mL(-1) of waterborne Escherichia coli (gram-negative) or Enterococcus faecalis (gram-positive) bacteria. The main factors determining the performance of the solar reactors are the type of photosensitizing material, the sensitizer loading, the CPC collector geometry (fin- vs coaxial-type), the fluid rheology, and the balance between concurrent photothermal--photolytic and 1O2 effects on the microorganisms' inactivation. In this way, at the 40 degrees N latitude of Spain, water can be disinfected on a sunny day (0.6-0.8 MJ m(-2) L(-1) accumulated solar radiation dose in the 360-700 nm range, typically 5-6 h of sunlight) with a fin-type reactor containing 0.6 m2 of photosensitizing material saturated with tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (ca. 2.0 g m(-2)). The optimum rheological conditions require laminar-to-transitional water flow in both prototypes. The fin-type system showed better inactivation efficiency than the coaxial reactor due to a more important photolytic contribution. The durability of the sensitizing materials was tested and the operational lifetime of the photocatalyst is at least three months without any reduction in the bacteria inactivation efficiency. Solar water disinfection with 1O2-generating films is demonstrated to be an effective technique for use in isolated regions of developing countries with high yearly average sunshine.

Mathematical models of cobalt and iron ions catalyzed microwave bacterial deactivation

Time differences for Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli survival during microwave irradiation (power 130 W) in the presence of aqueous cobalt and iron ions were investigated. Measured dependencies had “bell” shape forms with maximum bacterial viability between 1 – 2 min becoming insignificant at 3 minutes. The deactivation time for E. faecalis, S. aureus and E.coli in the presence of metal ions were smaller compared to a water control (4–5 min). Although various sensitivities to the metal ions were observed, S. aureus and E. coli and were the most sensitive for cobalt and iron, respectively. The rapid reduction of viable bacteria during microwave treatment in the presence of metal ions could be explained by increased metal ion penetration into bacteria. Additionally, microwave irradiation may have increased the kinetic energy of the metal ions resulting in lower survival rates. The proposed mathematical model for microwave heating took into account the “growth” and “death” factors of the bacteria, forming second degree polynomial functions. Good relationships were found between the proposed mathematical models and the experimental data for bacterial deactivation (coefficient of correlation 0.91 – 0.99).

Immediate root canal disinfection with ultraviolet light: an ex vivo feasibility study

OBJECTIVE

The study was designed to test application of ultraviolet light to root canal walls, as a mean of complementary immediate disinfection after the use of sodium hypochlorite.

STUDY DESIGN

Root canals were infected ex vivo with Enterococcus faecalis for 48 hours. Non-attached bacteria were washed away, and the remaining attached bacteria were subjected to disinfection, with 5% sodium hypochlorite alone or followed by exposure to ultraviolet light (254 nm, 300 mJ/cm(2)). Root canals were then tested for remaining viable bacteria. Canals were obturated and tested again after 14 days.

RESULTS

Sodium hypochlorite alone achieved negative cultures in only 47% of the cases, but 96% was achieved with sodium hypochlorite followed by ultraviolet light (P < .001). This status was also maintained after 14 days.

CONCLUSIONS

Illumination of root canals with ultraviolet light may be an effective supplementary means to achieve immediate disinfection of infected root canals.

Evaluation of the Bactericidal Effect of Er,Cr:YSGG, and Nd:YAG Lasers in Experimentally Infected Root Canals

The aim of this study was to evaluate the bactericidal effect of the Er,Cr:YSGG laser and the Nd:YAG laser in experimentally infected root canals. Sixty single-rooted teeth with straight canals were selected. After preparation and sterilization, the specimens were inoculated with Enterococcus faecalis for 3 weeks. After irradiation by lasers, the number of bacteria in each root canal was examined. The Er,Cr:YSGG laser gave a reduction of 77% after irradiation at 1 W and 96% at 1.5 W, but there was no significant difference (p > 0.05). The Nd:YAG laser gave a reduction of 97% at 1 W and 98% at 1.5 W, and there was no significant difference (p > 0.05). Compared with the Er,Cr:YSGG laser, the Nd:YAG laser is more effective (p < 0.05). In conclusion, both lasers systems have a significant bactericidal effect in infected root canals, and the Nd:YAG laser is more effective than the Er,Cr:YSGG laser.

Mathematical model of manganese ion catalyzed microwave deactivation of Enterococcus faecalis, Staphylococcus aureus and Escherichia coli

Enterococcus faecalis, Staphylococcus aureus and Escherichia coli survival was investigated using microwave irradiation (power 130 W) both in a water control and in the presence of a 1 microM manganese ion solution. Measured survival dependencies had "bell" shape form with maximum bacterial viability between 1-2 min of microwave heating. Additional heating revealed bacteria survival decreasing up to 3 min of microwave heating when viability became insignificantly small. The total deactivation time of bacteria in the presence of manganese ions was significantly smaller then that of bacteria irradiated in the microwave without manganese ions present (4-5 min). One possible explanation for the rapid reduction of bacterial survival during microwave irradiation in the presence of manganese ions is that increasing manganese ion penetration into bacteria along with microwave irradiation related to an increase of kinetic energy of ions, and damaging of bacteria by metal ions. The proposed mathematical model for microwave heating took into account "growth" and "death" factors of bacteria. It assumes that rates of bacterial growth and decay are linear functions of water temperature, and rate of bacterial decay that relates with metal concentration into water is also linear, which influenced the differential equation for the dependence between number of survival bacteria and temperature water. By using proportionality between the time of microwave heating and water temperature we derived the differential equation, between bacterial viability and time of microwave irradiation which was used as mathematical model for microwave heating in the presence of metal ions. This model had forms of second-degree polynomial functions. We received good relationships (with coefficient of correlation 0.92-0.99) between proposed mathematical model and experimental data for all bacterial deactivation.

Mathematical models for conventional and microwave thermal deactivation of Enterococcus faecalis, Staphylococcus aureus and Escherichia coli

Temperature dependencies of survival fecal coliforms such as Enterococcus faecalis, Staphylococcus aureus and Escherichia coli in water were investigated between 25-65 degrees C. Measured dependencies had "bell" shaped form with maximum bacterial viability at 35-45 degrees C. The rates of growth and decay of bacterial viability depend on specific forms of bacteria. At temperatures of 60-65 degrees C the number of viable bacteria decreased in one hundred times in comparison with the maximum value. Similar "bell" shape forms were found for dependencies between bacterial viability and time of microwave (dielectric) heating of water. The dependencies had maximum value at 1-2 min of microwave heating. Then, the number of viable bacteria decreased, and at 4-5 min of microwave heating, became insignificantly small. The proposed mathematical models for conventional and microwave heating took into account "growth" and "death" factors of bacteria, and had forms of second degree polynomial functions. The results showed good relationships (with coefficient correlation 0.84-0.99) between the proposed mathematical models and experimental data for both conventional and microwave heating.

Advanced noninvasive light-activated disinfection: assessment of cytotoxicity on fibroblast versus antimicrobial activity against Enterococcus faecalis

Recent interest in light-activated disinfection demands insight on the selectivity towards bacterial cells compared with mammalian cells. This study was aimed to evaluate the cytotoxicity and selectivity of an advanced noninvasive light-activated disinfection (ANILAD) developed in our laboratory. The extent of cytotoxic effect of methylene blue activated by visible light of wavelength 664 nm was tested and compared with sodium hypochlorite (NaOCl) under in vitro and ex vivo conditions on fibroblast L929 cells. Simultaneous evaluation of cytotoxicity and antibacterial effect was also conducted to study the specificity of light-activated therapy (LAT) toward prokaryotic cells (Enterococcus faecalis). The cytotoxicity was evaluated by 3-(4, 5-dimethylthiazol-2- yl)-2, 5-diphenyltetrazolium bromide assay and trypan blue viability test, whereas colony-forming units were determined to evaluate bacterial viability. Data from both in vitro and ex vivo experiments showed that cytotoxicity was significantly less in LAT compared with NaOCl (p<0.001). E faecalis cells were killed at a faster rate than fibroblasts. An irradiation dose producing 97.7% bacterial killing showed only 30% fibroblast dysfunction. This study indicated that ANILAD produced an insignificant effect on mammalian cells.

Sensitivity of oral bacteria to 254 nm ultraviolet light

AIM

To explore the sensitivity of bacteria commonly found in root canals to 254 nm ultraviolet (UV) light, either as individual cells or as participants of a bacterial multilayer.

METHODOLOGY

The sensitivity of oral bacteria, as individual cells, to UV light was tested by subjecting plates streaked with bacteria to 254 nm UV, at a fluence of 1-20 mJ cm(-2). An experimental model was designed to produce a bacterial multilayer and to study absorption of UV light by bacteria in an outer layer and its effect on the elimination of bacteria in the inner layer.

RESULTS

Direct exposure to relatively low doses of UV light (2-7 mJ cm(-2)) effectively eliminated all bacterial strains tested. Furthermore, an Enterococcus faecalis strain, partially resistant to a 24 h exposure to calcium hydroxide, was effectively eliminated within several seconds of exposure to UV light (P < 0.001). UV was absorbed by a multilayer of bacteria. When 4 bacterial cells microm(-2) were present in the light path, the UV light dose had to be increased by a factor of x10 to achieve 100% elimination of the bacteria in an inner layer.

CONCLUSIONS

The application of UV light to eliminate endodontic pathogens may be possible. Nevertheless, its absorbance by outer layers of bacteria should be considered and the UV light dose adapted accordingly.

Bactericidal effect of Nd:YAG laser irradiation on some endodontic pathogens ex vivo

AIM

To define the role of neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers in root canal disinfection along with a minimally invasive treatment concept.

METHODOLOGY

The hypothesis was tested ex vivo that Nd:YAG laser irradiation has a bactericidal effect on endodontic pathogens inoculated in root canals. Resultant colony-forming unit counts were associated with observations of bacterial cell structural changes using conventional scanning electron microscopy (CSEM) and environmental scanning electron microscopy (ESEM) on inoculated dentine surfaces, following indirect and direct Nd:YAG laser irradiation, respectively.

RESULTS

The Nd:YAG laser irradiation (1.5 W, 15 Hz, four times for 5 s) of Enterococcus faecalis inoculated canals resulted in a significant reduction (P < 0.05, Wilcoxon signed rank test) of the bacterial load, meaning a 99.7% kill, but no sterilization. The CSEM procedure verified that the extent of radiation damage was in line with the total amount of laser energy applied. After 2 h of incubation and three cycles of indirect laser treatment (i.e. through a 1-mm-thick dentine disc), no morphologically intact bacteria of Actinomyces naeslundii or Streptococcus anginosus were discernible. However, when micro-colonies of S. anginosus and specially biofilms of E. faecalis were present after 2 days, the in situ experiment using ESEM and direct laser treatment showed that bacterial eradication was reduced in deep layers.

CONCLUSIONS

The Nd:YAG laser irradiation is not an alternative but a possible supplement to existing protocols for canal disinfection as the properties of laser light may allow a bactericidal effect beyond 1 mm of dentine. Endodontic pathogens that grow as biofilms, however, are difficult to eradicate even upon direct laser exposure.

Disinfection of Root Canals Using Er:YAG Laser at Different Frequencies

OBJECTIVE

This study evaluated, in vitro, the degree of disinfection of the Er:YAG laser in root canals contaminated with Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans, for 28 days.

METHODS

Forty-six single-rooted human teeth were divided into five groups of eight teeth each; three teeth were used as negative controls and three as positive controls. After contamination, the root canals were prepared mechanically. Three groups were irradiated with Er:YAG laser at 100 mJ, varying the frequency (7, 10, and 16 Hz). Two groups were irrigated with 1.0% and 2.5% NaOCl solution. After treatment, two sterilized paper cones were placed in the root canals for 5 min. One cone was transferred to 2.0 mL of Letheen broth culture medium, incubated at 37 degrees C for 48 h, and then 0.1 mL of that solution was placed in 2.0 mL of brain heart infusion for 48 h to determine microbial growth. The other cone was transferred to a test pipette with peptone and water for serial dilution and spread in Müeller Hinton medium. After 24 h of incubation, the colony-forming units (CFUs) were counted.

RESULTS

There was a microbial reduction of 85.33% for the group irradiated with Er:YAG laser at 100 mJ/7 Hz, 74.58% at 100 mJ/10 Hz, and 89.50% at 100 mJ/16 Hz. For the groups irrigated with 1.0% and 2.5% NaOCl solution, 83.15% and 84.46% values of microbial reduction were obtained respectively.

CONCLUSION

All the groups showed statistically similar results (p > 0.05%). No method totally eliminated microorganisms.

The recombination deficient Enterococcus faecalis UV202 strain is a recA mutant

The recA gene of the recombination deficient Enterococcus faecalis strain UV202 was sequenced and found to encode a glycine to aspartic acid mutation at amino acid 265. Both the UV sensitive and recombination deficient phenotypes of the UV202 strain were complemented by expression of the wild-type recA gene cloned under the control of the nisin-inducible promoter of an expression vector.

Testing of a Dual-Mode Microwave Care Regimen for Hydrogel Lenses

PURPOSE

To test the design of a patient care regimen for soft lenses that aims to provide the highest standards of disinfecting through use of domestic microwave cookers, while also providing storage equipment and solution that enable patients to follow a conventional cold disinfecting regimen when traveling. The cleaning efficacy of surfactant agents during microwave treatment was also considered.

METHODS

The microbiologic performance of the regimen and its disinfecting apparatus was tested according to the Food and Drug Administration (FDA) protocols for contact lens heat disinfectors. Subsequently, a prospective pilot clinical trial of the regimen involving 15 subjects was carried out to the protocols of the FDA and International Standards Organization 11,980:1997.

RESULTS

Lenses inoculated with 10(7) colony-forming units (cfu) of Enterococcus faecalis were disinfected to 0 cfu by a 12-s irradiation of a compact disinfecting case that held the lenses suspended in 12 ml saline. A proof of operation indicator performed correctly for all 10 cases tested. No adverse reactions were found in the pilot patient trial, using Renu multipurpose (Bausch and Lomb, Rochester, NY) as the test solution, and no statistically significant difference was found between test and control groups in respect of any sign. However, the greater incidence of edema, palpebral hyperemia, and lens front-surface deposition in the microwave test group may be clinically significant.

CONCLUSIONS

The design of the test care regimen proved easy for patients to follow in either hot or cold disinfecting mode. The greater incidence of certain signs in the microwave test group suggests the need to continue using a rub and rinse step for the microwave mode and for additional investigation into the choice of an appropriate multipurpose solution formulation for this proposed regimen, preferably one that does not use a block copolymer-type surfactant agent.

Bactericidal effect of a 980-nm diode laser in the root canal wall dentin of bovine teeth

OBJECTIVE

The aim of this in vitro study was to investigate the antibacterial depth effect of continuous wave laser irradiation with a wavelength of 980 nm in the root canal wall dentin of bovine teeth.

BACKGROUND DATA

The long-term success of an endodontic therapy often fails due to remaining bacteria in the root canal or dentin tubules, which cannot be sufficiently eliminated through the classical root canal preparation technique nor through rinsing solutions.

MATERIALS AND METHODS

A total of 102 slices of bovine root dentin of different thicknesses (100, 300 and 500 micro m) were prepared. The samples were inoculated from one side with 5 micro L of an enterococcus faecalis suspension of defined concentration. Four slices per slice thickness served as a control group; the rest of the 30 slices per thickness were subjected to laser irradiation - 10 each of these slices were irradiated with distal outputs of 1.75, 2.3, and 2.8 Watts (W). After drying them for 30 sec, the back of the inoculated dentin slice was irradiated for 32 seconds with a 200- micro m fiber optical waveguide under constant movement of the fibers. The remaining bacteria were then detached in NaCl under vibration. The eluate produced by this was - taking account of the degree of dilution - plated out on sheep blood agar plates. After 24 h of incubation, the grown bacterial colonies were able to be counted out and evaluated. By doing so, they were compared with the non-irradiated, but otherwise identically treated control group.

RESULTS

With a slice thickness of 100 micro m, the 980-nm diode laser achieved a maximum bacterial reduction of 95% at 1.75 W, 96% at 2.3 W, and 97% at 2.8 W. With a slice thickness of 300 micro m, a maximum of 77% of the bacteria was destroyed at 1.75 W, 87% at 2.3 W, and 89% at 2.8 W. The maximum bacterial reduction with a slice thickness of 500 micro m was 57% at 1.75 W, 66% at 2.3 W, and 86% at 2.8 W.

CONCLUSION

The results of this research show that the 980-nm diode laser can eliminate bacteria that have immigrated deep into the dentin, thus being able to increase the success rate in endodontic therapy.

Evaluation Of The Antimicrobial Effect Of Er:YAG Laser Irradiation Versus 1% Sodium Hypochlorite Irrigation For Root Canal Disinfection

This laboratory study evaluated Er:YAG laser antibacterial action in infected root canals. Forty-eight maxillary central incisors were used. After canal preparation, the teeth were autoclaved and divided into four groups: (1) non-treated teeth (control group); (2) teeth treated with NaOCl; (3) teeth irradiated with Er:YAG laser (7 Hz, 100 mJ, 80 pulses/canal, 11 sec) to the working length; (4) teeth irradiated similarly to, but 3 mm short, of the apex. The root canals from Groups 2, 3 and 4 were inoculated with 4 bacteria: Bacillus subtillus, Enterococcus faecalis, Pseudomonas aeruginosa, and Staphylococcus aureus, together with Candida albicans, and maintained for 24 h at 37 degrees C. All suspensions were adjusted to tube 2 of the MacFarland scale. The intracanal material was then collected with sterile paper points, which were placed in the canals for 5 min and then immersed in 5 ml of BHI medium. This was then seeded onto agar and stained by Gram's method. The NaOCl solutions and the Er:YAG laser irradiation to working length were effective against all five micro-organisms; however, 70% of the specimens irradiated 3 mm short of the apex remained infected.

The bactericidal effect of Nd:YAG, Ho:YAG, and Er:YAG laser irradiation in the root canal: an in vitro comparison

OBJECTIVE

The aim of this study was to compare the antibacterial effectiveness of the Nd:YAG, the Ho:YAG, and the Er:YAG laser in infected root canals.

SUMMARY BACKGROUND DATA

Lasers are gaining increasing importance in the field of endodontics. Numerous studies have shown the beneficial effects of laser treatment in disinfecting root canals.

METHODS

In our in vitro experimental setup, 40 extracted and endodontically treated teeth were inoculated with a suspension of Escherichia coli and Enterococcus faecalis and then irradiated at standardized power settings. The disinfecting efficacy of each laser was proved by classical microbiological examination.

RESULTS

This article highlights that all three lasers substantially decreased the bacterial population with only minimal differences in their microbicidal efficacy. At 1.5 W, the best results were obtained by the Er:YAG laser achieving a mean bacterial elimination of 99.64%, followed by the Nd:YAG laser (99.16%), and the Ho:YAG laser (99.05%).

CONCLUSION

Our findings indicate that all three lasers act as strongly effective microbicides without causing unfavorable temperature rises at the settings used. They can thus be considered a valuable tool for root canal treatment.

The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples.

High-performance, low-cost solar collectors for disinfection of contaminated water

Although the germicidal action of sunlight has long been recognized, its potential for practical applications has to be researched more thoroughly. This paper summarizes the progress made toward a commercially practical collector for solar disinfection applications. Nontracking compound parabolic collectors (CPCs), developed originally for capturing solar photons for thermal energy applications, were examined as potential solar photoreactors. A field demonstration of solar disinfection treatment using commercially manufactured solar reactors was conducted. Field tests showed successful destruction of Escherichia coli and Enterococcus faecalis and have provided data for full-scale design of water treatment systems. From above observations, a throughput value of 50 L/m2 h for the low-cost CPC reactor tested was estimated. For a 190 m3/d (0.05 MGD) facility, the estimated total costs for disinfection using UV-A is U.S. $0.19/m3 ($0.70/1000 gal). The use of near-UV sunlight to disinfect water supplies seems promising in rural communities of developing countries where treated water is unavailable.

Morphologic changes correlating to different sensitivities of Escherichia coli and enterococcus faecalis to Nd:YAG laser irradiation through dentin

BACKGROUND AND OBJECTIVE

Previous studies demonstrated the disinfecting potential of Nd:YAG laser irradiation on the root canal system from an overall quantitative viewpoint. The aim of this study was to evaluate the specific effect of irradiation through dentin on gram-negative and gram-positive bacteria with regard to their cell structure.

STUDY DESIGN/MATERIALS AND METHODS

Sterile dentin samples of standardized size were divided into two sets of four groups with eight samples each. The first set was inoculated with Escherichia coli as the gram-negative test strain, the second set was inoculated with Enterococcus faecalis, which served as the gram-positive test organism. The samples were then irradiated on the bacteria-free side in contact mode under constant scanning movement at an angle of 10 degrees by use of the fiber optic of the Nd:YAG laser. Upon laser treatment they were critical point dried and subjected to SEM investigation. Another two sets of samples were prepared and irradiated in the same manner and evaluated by standard microbiological procedures to verify whether the observed morphologic alterations correlated to cell death.

RESULTS

SEM investigations revealed damage pattens that increased with the amount of energy applied. Whereas the gram-negative test organism showed immediate structural injury, the gram-positive test organism required repeated application of irradiation. The microbiological examination showed reduction of both bacterial strains, yet to different extents.

CONCLUSION

Our study demonstrates the different morphologic impact of Nd:YAG laser irradiation through dentin on representatives of the two main groups of bacteria. It shows that the construction of the cell wall is crucial for their individual sensitivity to laser treatment.

Diode laser radiation and its bactericidal effect in root canal wall dentin

OBJECTIVES

The aim of this study was to investigate the antibacterial effect of a diode laser in deep root canal dentin.

BACKGROUND DATA

The microbial colonization of root canal dentin can lead to failures in conventional endodontic treatment if an inadequate bacterial reduction only is achieved through canal treatment and chemical disinfection.

METHODS

100 microm, 300 microm and 500 microm bovine dentin slices obtained by longitudinal sections were sterilized and inoculated on one side with an Enterococcus faecalis suspension. Laser radiation was performed on the opposite side with the diode laser (810 nm) at a setting of 3 W in continuous mode (CW). Radiation was performed using a 400-microm tapered fiber tip at an angle of approximately 5 degrees to the surface over a period of 30 seconds. The output power at the distal end of the tip was 0.6 W. The bacteria were then eluted through vibration and cultured on blood agar plates. The colony count reflected the antibacterial effect of laser radiation as a function of the layer thickness.

RESULTS

A mean bacterial reduction of 74% was achieved even with a 500-microm thick slice.

CONCLUSION

This investigation indicates that the diode laser radiation reduces the number of bacteria in deep layers of infected root canal wall dentin.

The bactericidal effect of Ho:YAG laser irradiation within contaminated root dentinal samples

OBJECTIVE

This in vitro study investigates the bactericidal effect of pulsed Ho:YAG laser irradiation in the depth of contaminated dentin specimens.

BACKGROUND DATA

Previous studies have shown the effectiveness of laser irradiation in bacterial reduction of infected root canal.

METHODS

Root dentin of bovine teeth were sliced longitudinally in 180 samples of 100 microm, 300 microm, and 500 microm thickness, sterilized, dried, and inoculated on one side, with 1 microL of Enterococcus faecalis suspension. The opposite side's were irradiated four times for 5 seconds each with Ho:YAG laser irradiation, a wavelength of 2.10 microm, using four different energy settings: 1 W/5 Hz; 1 W/10 Hz; 1.5 W/5 Hz, and 2.0 W/5 Hz through a 320-microm quartz fiber at an angle of approximately 5 degrees. In addition, two control groups were investigated, the first was inoculated and not submitted to any treatment, the second was inoculated and treated with NaOCl and H2O2. The remaining bacteria from each dentin sample in a transport media were removed by vibration, serially diluted, and plated out on culture dishes selective for Enterococcus faecalis.

RESULTS

When compared with the untreated control group or even with the group treated with NaOCl plus H2O2, counting of colonies forming units (CFU) from the laser-treated samples revealed a high significant bacterial elimination with a maximum of 98.46% and a minimum of 83.65%.

CONCLUSIONS

Our findings demonstrate a significant decrease of the bacterial population in depth, suggesting that the Ho:YAG laser irradiation could be effective to eliminate the microorganisms harbored within dentin or contaminated canals.

Bactericidal action of 308 nm excimer-laser radiation: an in vitro investigation

The aim of the present study was to investigate the influence of 308 nm excimer-laser radiation on bacterial growth. Six different bacterial strains (Staphylococcus aureus, Escherichia coli, Streptococcus faecalis, Lactococcis lactis, Salmonella typhimurium, and Deinococcus radiodurans) were exposed in vitro to various doses and energy densities of laser radiation. To exclude bacterial killing by supraphysiological heating, the temperature change in the samples during irradiation was measured. Extended antimicrobial effects of XeCl excimer-laser radiation depending on the time of radiation, the energy density of the laser beam, and the irradiated bacterial strain were observed. Reduction of bacterial growth is independent of temperature and not linked to any ablative tissue removal. In almost all cases, a 99.9% reduction of bacteria was reached by total radiation times < 100 ms. The proven antimicrobial effects of 308 nm excimer-laser radiation may be of significant clinical importance in endodontics and periodontology in the future.

The effects of ultraviolet radiation on antibiotic-resistant bacteria in vitro

Wound infections produced by antibiotic-resistant bacterial strains are particularly difficult to manage. This study examined the effectiveness of ultraviolet (UV) light treatment in killing antibiotic-resistant strains of Staphylococcus aureus and Enterococcus faecalis in vitro. Between 2 and 5 replications of each organism at 10(8) organisms/ml were prepared and plated on sheep blood agar medium and treated with UV light (254 nm, 15.54 mW/cm2 output). Irradiation times were 0, 2, 5, 8, 15, 30, 45, 60, 90 or 120 seconds. Bacterial cultures were then incubated at 35 degrees C for 24 hours. Kill rates were 99.9 percent for the methicillin-resistant strain of S. aureus (MRSA) at 5, 8, 15, 30, 45, 60 seconds and 100 percent at 90 and 120 seconds. Kill rates were 99.9 percent at 5, 8, 15, 30 seconds for vancomycin-resistant E. faecalis (VRE) and 100 percent at 45, 60, 90, 120 seconds. Similar results were found with UV light treatment of the antibiotic-susceptible strains of S. aureus and E. faecalis. A significant difference in kill rates at 30 seconds of UV exposure was detected between the antibiotic-resistant strain of S. aureus and the antibiotic-resistant strain of E. faecalis (Student's t test, p < 0.01). Significant differences were also detected in the kill rates at 30 second exposure times for the antibiotic-susceptible strains of S. aureus and E. faecalis. These findings suggest that the Enterococcal bacteria is more susceptible to the killing effects of UV. This data also suggests that UV light at 254 nm is bactericidal for antibiotic-resistant strains of S. aureus and E. faecalis at times as short as 5 seconds and that the enterococcal bacteria is more susceptible to the killing effects of UV. With recommended patient treatment times for infected wounds being significantly longer than 5 seconds, this data indicates that patient treatment times need to be re-examined.

[4-Nitroquinoline-1-oxide induced adaptive and cross resistance to ultraviolet rays and nalidixic acid in Enterococcus faecalis]

The resistance of Enterococcus faecalis to exposure to 4-nitroquinoline-1-oxide (4-NQO) as well as to UV irradiation and nalidixic acid was shown to increase as a result of reinoculations in medium containing 4-NQO. Irradiation of cells with UV254 (20, 60, or 100 J/m2) did not increase their resistance to 4-NQO. The desmutagenic activity of 4-NQO-adapted cells in the case of mutagenesis induced by 4-NQO was higher than in control cells. The mechanism of induced resistance is discussed.