Red cabbage extract immobilized in bacterial cellulose film as an eco-friendly sensor to monitor microbial contamination and gamma irradiation of stored cucumbers.

The aim of the present study is to develop a pH-sensing biopolymer film based on the immobilization of red cabbage extract (RCE) within bacterial cellulose (BC) to detect contamination and gamma radiation exposure in cucumbers. The results obtained show a sensitivity to pH changes for RCE in its aqueous form and that incorporated within BC films (RCE-BC), both showed color change correlated to bacterial growth (R2 = 0.91), this was supported with increase in pH values from 2 to 12 (R2 = 0.98). RCE and RCE-BC exposure to gamma radiation (0, 2.5, 5, 10, 15, 20, 25 kGy) resulted in gradual decrease in color that was more evident in RCE aqueous samples. To sense bacterial contamination of cucumbers, the total count was followed at 0, 5, 10 and 15 days in cold storage conditions and was found to reach 9.13 and 5.47 log cfu/mL for non-irradiated and 2 kGy irradiated samples, respectively. The main isolates detected throughout this storage period were identified as Pseudomonas fluorescens, Erwinia sp. Pantoea agglomerans using matrix assisted laser desorption ionization-time of flight-ms (MALDI-TOF-MS). Bacterial growth in stored irradiated cucumbers was detected by color change within 5 and 10 days of storage, after which there was no evident change. This is very useful since contamination within the early days of storage cannot be sensed with the naked eye. This study is the first to highlight utilizing RCE and RCE-BC as eco-friendly pH-sensing indicator films for intelligent food packaging to detect both food contamination and gamma preservation for refrigerator stored cucumbers.

Thermo-resistance of ESKAPE-panel pathogens, eradication and growth prevention of an infectious biofilm by photothermal, polydopamine-nanoparticles in vitro.

Nanotechnology offers many novel infection-control strategies that may help prevent and treat antimicrobial-resistant bacterial infections. Here, we synthesized polydopamine, photothermal-nanoparticles (PDA-NPs) without further surface-functionalization to evaluate their potential with respect to biofilm-control. Most ESKAPE-panel pathogens in suspension with photothermal-nanoparticles showed three- to four-log-unit reductions upon Near-Infra-Red (NIR)-irradiation, but for enterococci only less than two-log unit reduction was observed. Exposure of existing Staphylococcus aureus biofilms to photothermal-nanoparticles followed by NIR-irradiation did not significantly kill biofilm-inhabitants. This indicates that the biofilm mode of growth poses a barrier to penetration of photothermal-nanoparticles, yielding dissipation of heat to the biofilm-surrounding rather than in its interior. Staphylococcal biofilm-growth in the presence of photothermal-nanoparticles could be significantly prevented after NIR-irradiation because PDA-NPs were incorporated in the biofilm and heat dissipated inside it. Thus, unmodified photothermal nanoparticles have potential for prophylactic infection-control, but data also constitute a warning for possible development of thermo-resistance in infectious pathogens.

Thinking Outside the Treatment Plant: UV for Water Distribution System Disinfection.

This work critically evaluates the current paradigm of water distribution system management and juxtaposes that with the potential benefits of employing UV irradiation, which we hope will catalyze a judicial re-evaluation of the current practices in water distribution system management and spur critical research and a new way of thinking about secondary disinfection across the extent of distribution systems. Given the recent advances in UV technology and the efficacy of UV disinfection against all pathogen classes, we now see UV applications for disinfection in many aspects of consumers lives: in water coolers, dishwashers, coffee makers, and disinfection of personal items like gym bags, water bottles, and toothbrushes. Public and regulatory concern over water quality and pathogens, especially the recent interest in building plumbing, calls out for new approaches to disinfection and distribution system management. We envision a new model for secondary disinfection in water distribution systems utilizing emerging germicidal UV LED-based disinfection. UV irradiation in water treatment can achieve high levels of disinfection of all pathogens and minimize or eliminate the formation of regulated disinfection byproducts. So why is UV not considered as a secondary disinfectant for distribution systems? In this Account, we lay out the logic as to the benefits and practicality of adding distributed UV treatment to assist in protection of distribution systems and protect water quality for human exposure. The possible locations of UV irradiation in distribution systems are envisioned, potentially including UV booster stations along the distribution network, UV in storage tanks or their inlet/outlets, LEDs distributed along pipe walls, small point of use/entry treatment systems for buildings/homes/taps, or submersible swimming or rolling UV LED drones to reach problem pipes and provide a "shock" treatment or provide sterilization after main breaks or repairs. The benefits of UV applications in water also include high effectiveness against chlorine-resistant protozoa, no added disinfection byproducts, and compatibility of adding of UV to existing secondary disinfection strategies for enhanced protection. Potential challenges and research needs are described, such as use of UV-compatible pipe materials, implementation of sensors to monitor distributed LEDs, management of waste heat from the rear surface of the LED, and understanding the potential for regrowth of opportunistic microorganisms. Another notable challenge is the relatively stagnant regulatory environment in some countries to develop frameworks for evaluation and acceptance of UV technology in distribution systems that require a chemical secondary disinfectant. Rapid advances in UV LED research has propelled the growth of this field, but needs still remain, including understanding behavior of biofilms in pipes under UV irradiation, including any beneficial effects that may be lost, the potential for fouling of LED emission surfaces and monitoring points, and provision of a distributed power network to run the LEDs. Regulators may want specific monitoring approaches and advances in real-time monitoring of microbial viability, and engineers may need to develop new approaches to overall management.

Effect of temperature and ultraviolet light on the bacterial kill effectiveness of antibiotic-infused 3D printed implants.

Drug eluting 3D printed polymeric implants have great potential in orthopaedic applications since they are relatively inexpensive and can be designed to be patient specific thereby providing quality care. Fused Deposition Modeling (FDM) and Stereolithography (SLA) are among the most popular techniques available to print such polymeric implants. These techniques facilitate introducing antibiotics into the material at microscales during the manufacturing stage and subsequently, the printed implants can be engineered to release drugs in a controlled manner. However, FDM uses high temperature to melt the filament as it passes through the nozzle and SLA relies on exposure to nanoscale wavelength ultraviolet (UV) light which can adversely affect the anti-bacterial effectiveness of the antibiotics. The focus of this article is two-fold: i) Examine the effect of high temperature on the bacterial kill-effectiveness of eluted antibiotics through Polycaprolactone (PCL) based femoral implants and ii) Examine the effect of exposure to ultraviolet (UV) light on the bacterial kill-effectiveness of eluted antibiotics through femoral implants made up of a composite resin with various weight fractions of Polyethylene Glycol (PEG) and Polyethylene Glycol Diacrylate (PEGDA). Results indicate that even after exposing doxycycline, vancomycin and cefazolin at different temperatures between 20oC and 230oC, the antibiotics did not lose their effectiveness (kill radius of at least 0.85 cm). For doxycycline infused implants exposed to UV light, it was seen that a resin with 20 % PEGDA and 80 % PEG had the highest efficacy (1.8 cm of kill radius) and the lowest efficacy was found in an implant with 100 % PEGDA (1.2 cm of kill radius).

Recent Progress in Two-Dimensional Antimicrobial Nanomaterials.

Nowadays, microorganisms, including bacteria and viruses, are regarded as new environmental pollutants and pose serious threats to public health. Yet, traditional disinfection approaches for bacteria and viruses are generally ineffective. Furthermore, they exhibit the disadvantages of high-energy consumption, environmental pollution, high cost, and toxic byproduct generation. In this respect, nanomaterials display promising antimicrobial capabilities due to their unique properties and provide solutions to the abovementioned issues. Herein, recent progress in the development of 2D nanomaterials displaying antimicrobial capabilities is highlighted. The structures, morphologies, and performances of essential metal, graphene, and nitride-based 2D antibacterial nanomaterials are summarized in detail. In addition, possible antimicrobial mechanisms and the relationship between structure and antimicrobial efficiency are elaborated.

Composite Films with UV-Barrier Properties of Bacterial Cellulose with Glycerol and Poly(vinyl alcohol): Puncture Properties, Solubility, and Swelling Degree.

The aim of this study was to develop composite films based on bacterial cellulose, glycerol, and poly(vinyl alcohol) with improved optical and mechanical properties and good UV-barrier property. The interaction among the compounds was analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. The mechanical properties (toughness, burst strength, and distance to burst), solubility, water adsorption, and light barrier properties of the composite films were evaluated. Polynomial models obtained allowed us to predict the behavior of these properties. Poly(vinyl alcohol) showed a reinforcing effect on the bacterial cellulose matrix, while glycerol showed a noticeable plasticizing behavior. The bacterial cellulose-based composites showed toughness values ranging from 0.22 to 2.60 MJ/m3. The burst strength values obtained ranged between 43.74 and 2105.52 g. The distance to burst ranged from 0.39 to 4.94 mm. The film solubility on water ranged from 9.37 to 31.65%, and the water retention ranged from 78.26 to 364.78%. Glycerol decreased the transmittance in the UV region, improving the UV-barrier properties of the films, while poly(vinyl alcohol) improved the transparency and opacity values of the samples. The transmittance in the UV regions (A, B, and C) ranged from 1 to 48.51%, increasing with the poly(vinyl alcohol) concentration.

What Is the Role of Diagnostic and Therapeutic Sonication in Periprosthetic Joint Infections?

BACKGROUND: Periprosthetic joint infection (PJI) is one of the most dreaded complications in joint replacement surgery. Diagnosis and treatment can be difficult and biofilms are of major concern due to their low susceptibility toward antibiotics. METHODS: This review focuses on the use of sonication as an evolving diagnostic and adjunct treatment modality in the context of PJI. Therapeutic application of sonication is discussed separately for its (i) direct action on bacteria, (ii) synergistic effects with antibiotics, and (iii) effects on release of antibiotics from bone cement. RESULTS: Used as a diagnostic tool, sonication shows promising results with respect to sensitivity and specificity when compared to conventional methods, notably after previous administration of antibiotics. As an adjunct treatment modality, the chemical, physical, and mechanical effects of sonication are primarily driven by cavitation and recognized as the main cause for bactericidal effects but the exact underlying mechanisms have not been identified yet. Sonication alone does not have the ability to completely eradicate biofilms but synergistic effects when used in conjunction with antibiotics have been reported. There is also evidence for enhanced antibiotic release from bone cement. CONCLUSION: Sonication is as an evolving modality in the context of PJIs. As a diagnostic tool, it has not been introduced in routine clinical practice and sonication as a treatment modality in PJIs is still in an experimental stage. Factors such as frequency, pressure, chemical activity, intensity, and exposure time need to be evaluated for optimal application of sonication and may also improve study comparison.

Medically important biofilms and non-thermal plasma.

In recent decades, the non-thermal plasma, i.e. partially or completely ionized gas produced by electric discharges at ambient temperature, has become of interest for its microbiocidal properties with potential of use in the food industry or medicine. Recently, this interest focuses not only on the planktonic forms of microorganisms but also on their biofilms. The works in this interdisciplinary field are summarized in this review. The wide range of biofilm-plasma interactions is divided into studies of general plasma action on bacteria, on biofilm and on its oral and dental application; a short overview of plasma instrumentation is also included. In addition, not only biofilm combating but also an important area of biofilm prevention is discussed. Various DC discharges of the point-to-plane type. Author's photograph, published in Khun et al. (Plasma Sources Sci Technol 27:065002, 2018).

Clinical efficacy of EDTA ultrasonic activation in the reduction of endotoxins and cultivable bacteria.

AIM: This clinical study was conducted to investigate the influence of 17% ethylenediaminetetraacetic acid (EDTA) ultrasonic activation after chemomechanical preparation (CMP) on eliminating/reducing oral bacterial lipopolysaccharides (known as endotoxins) and cultivable bacteria in teeth with pulp necrosis and apical periodontitis. METHODOLOGY: Samples were taken from 24 root canals at several clinical periods: S1 - before CMP; S2 - after CMP; S3 - after EDTA: G1 - with ultrasonic activation (n = 12) and G2 - without ultrasonic activation (n = 12). Root canals were instrumented using Mtwo rotary files. Culture techniques were used to determine the number of colony-forming units (CFU). Limulus amebocyte lysate (LAL) was used to measure endotoxin levels. Friedman's and Wilcoxon signed-rank tests were used to compare the amount of bacteria and endotoxin levels in each period (P < 0.05). RESULTS: Endotoxins and cultivable bacteria were recovered in 100% of the initial samples (S1). CMP was effective in reducing endotoxins and bacterial load (all with P < 0.05). Higher values of endotoxin reduction were achieved with EDTA ultrasonic activation [G1, 0.02 EU mL-1 (range 0.01-0.75)] compared with the no activation group [G2, 1.13 EU mL-1 (range 0.01-8.34)] (P < 0.05). Regarding bacterial reduction, no statistically significant difference was found in S3, regardless of the group (G1, G2, P > 0.05). CONCLUSIONS: Chemomechanical preparation was effective in reducing bacteria and endotoxins, but could not completely eliminate them. The ultrasonic activation of EDTA was effective in further reducing endotoxin levels in the root canals of teeth with pulp necrosis and apical periodontitis.

Can ultraviolet light C decrease the environmental burden of antimicrobial-resistant and -sensitive bacteria on textiles?

BACKGROUND: The environment is important in transmission of bacteria. Textiles are difficult and time consuming to clean; ultraviolet light C (UVC) is germicidal and may be an effective disinfection method for textile surfaces. OBJECTIVE: This study evaluated the efficacy of UVC, a commercial quaternary ammonium compound antimicrobial spray (FAS) and UVC+FAS combined for reducing bacterial colonization on experimentally contaminated textiles. METHODS: Microfibre, cotton and polyester were inoculated with meticillin-sensitive and -resistant Staphylococcus aureus (MSSA and MRSA), Staphylococcus pseudintermedius (MSSP and MRSP), Pseudomonas aeruginosa or Escherichia coli. ATCC® strains were used except for MRSP, for which ten canine clinical isolates were collected. Textiles were treated with three doses of UVC (13 mJ/cm2 , 54 mJ/cm2 or 270 mJ/cm2 ), FAS or both (FAS and UVC at 270 mJ/cm2 ). UVC was delivered using a modified mercury-based lamp. Bleach (8.25%) was used as a positive control. Negative controls received no treatment. Surface bacterial counts were determined 24 h post-treatment. RESULTS: The lower dosages (13 mJ/cm2 and 54 mJ/cm2 ) of UVC had >90% colony forming unit (CFU) reduction, 270 mJ/cm2 had >99% CFU reduction and combined UVC+FAS had 100% CFU reduction against all bacterial strains on all surfaces (P < 0.05). Ten experiments showed that treatment with UVC had a greater CFU reduction when compared to FAS alone (P < 0.05). A majority of those experiments (seven of 10) involved Gram-negative species (P. aeruginosa or E. coli). CONCLUSION: UVC quickly reduced the bacterial burden on textiles to greater than 90%; UVC may be a better disinfecting agent than FAS for Gram-negative species.

Clinical-microbiological research of action ozone therapy and light-emetting diode radiation of red range (630 nanometers) on microflora of the hole extracted toothatalveolitis and limited osteomyelitis of jaws. / Kliniko-mikrobiologicheskoe issledovanie deistviya ozonoterapii i svetodiodnogo izlucheniya krasnogo diapazona (630 nm) na mikrofloru lunki udalennogo zuba pri al'veolite i ogranichennom osteomielite chelyustei.

As a result of cliniko-microbiological research the data testifying to substantial improvement of efficiency of antimicrobictherape at inclusion in a complex of medical actions at alveolitis and the limited osteomyelitis of a jow ozone therapy in a combination with a light-emettinf diode irradiation of the hole extracted teeth red ( 630 nanometers) are obtained by light.

Novel Broad-Spectrum Antimicrobial Photoinactivation of In Situ Oral Biofilms by Visible Light plus Water-Filtered Infrared A.

Antimicrobial photodynamic therapy (APDT) has gained increased attention as an alternative treatment approach in various medical fields. However, the effect of APDT using visible light plus water-filtered infrared A (VIS + wIRA) on oral biofilms remains unexplored. For this purpose, initial and mature oral biofilms were obtained in situ; six healthy subjects wore individual upper jaw acrylic devices with bovine enamel slabs attached to their proximal sites for 2 h or 3 days. The biofilms were incubated with 100 µg ml(-1) toluidine blue O (TB) or chlorin e6 (Ce6) and irradiated with VIS + wIRA with an energy density of 200 mW cm(-2) for 5 min. After cultivation, the CFU of half of the treated biofilm samples were quantified, whereas following live/dead staining, the other half of the samples were monitored by confocal laser scanning microscopy (CLSM). TB- and Ce6-mediated APDT yielded a significant decrease of up to 3.8 and 5.7 log10 CFU for initial and mature oral biofilms, respectively. Quantification of the stained photoinactivated microorganisms confirmed these results. Overall, CLSM revealed the diffusion of the tested photosensitizers into the deepest biofilm layers after exposure to APDT. In particular, Ce6-aided APDT presented elevated permeability and higher effectiveness in eradicating 89.62% of biofilm bacteria compared to TB-aided APDT (82.25%) after 3 days. In conclusion, antimicrobial photoinactivation using VIS + wIRA proved highly potent in eradicating oral biofilms. Since APDT excludes the development of microbial resistance, it could supplement the pharmaceutical treatment of periodontitis or peri-implantitis.

Effectiveness of UV-C radiation in inactivation of microorganisms on materials with different surface structures.

INTRODUCTION AND OBJECTIVE: Ultraviolet light in the UV-C band is known as germicidal radiation and was widely used for both sterilization of the equipment and creation of a sterile environment. The aim of the study is to assess the effectiveness of inactivation of microorganisms deposited on surfaces with various textures by UV-C radiation disinfection devices. MATERIAL AND METHODS: Five microorganisms (3 bacteria, virus, and fungus) deposited on metal, plastic, and glass surfaces with smooth and rough textures were irradiated with UV-C light emitted by low-pressure mercury lamp and ultraviolet emitting diodes (LEDs), from a distance of 0.5 m, 1 m, and 1.5 m to check their survivability after 20-minute exposure. RESULTS AND CONCLUSIONS: Both tested UV-C sources were effective in inactivation of microorganisms; however, LED emitter was more efficient in this respect than the mercury lamp. The survival rate of microorganisms depended on the UV-C dose, conditioned by the distance from UV-C source being the highest at 0.5 m and the lowest at 1.5 m. For the tested microorganisms, the highest survival rate after UV-C irradiation was usually visible on glass and plastic surfaces. This observation should be considered in all environments where the type of material (from which the elements of technical equipment are manufactured and may be contaminated by specific activities) is important for maintaining the proper level of hygiene and avoiding the unwanted and uncontrolled spread of microbiological pollution.

Bactericidal effects of hematoporphyrin monomethyl ether-mediated photosensitization against pathogenic communities from supragingival plaque.

Photodynamic antimicrobial chemotherapy (PACT) is proposed as a potential candidate to inactivate pathogens in localized infections due to the rapid evolution of bacterial resistance. The treatment modality utilizes nontoxic agents called photosensitizers and harmless visible light to generate reactive oxygen species which result in microbial cells' killing. Hematoporphyrin monomethyl ether (HMME) as a novel and affordable photosensitizer has been used in treating various clinical diseases for years, but few applications in infection. In this report, we studied the bactericidal effects of the HMME-mediated photodynamic reaction on the pathogenic microbes in supragingival plaque which can lead to many oral infectious diseases such as caries, gingivitis, and so on. Our findings demonstrated that HMME promoted an effective action in bacterial reduction with the application of laser energy. Moreover, the antimicrobial activities were dramatically enhanced as the HMME concentration and exposure time were increased, but reached a plateau when matched the appropriate agent concentration and illumination. It was found that the survival fraction of microorganisms is exponentially dependent on the product of HMME concentration and irradiation time. These promising results suggest the HMME may be an excellently cost-effective photosensitizing agent for mediating PACT in the treatment of supragingival plaque-related diseases. An optimized HMME concentration and irradiation time has been found to achieve the best results under our experimental conditions. The high HMME concentration matching short curative time, or vice versa, can achieve the similar therapeutic effect, which may provide more flexible treatment plans according to specific conditions.

Drinking water biofilms on copper and stainless steel exhibit specific molecular responses towards different disinfection regimes at waterworks.

Biofilms growing on copper and stainless steel substrata in natural drinking water were investigated. A modular pilot-scale distribution facility was installed at four waterworks using different raw waters and disinfection regimes. Three-month-old biofilms were analysed using molecular biology and microscopy methods. High total cell numbers, low counts of actively respiring cells and low numbers of cultivable bacteria indicated the high abundance of viable but not cultivable bacteria in the biofilms. The expression of the recA SOS responsive gene was detected and underlined the presence of transcriptionally active bacteria within the biofilms. This effect was most evident after UV disinfection, UV oxidation and UV disinfection with increased turbidity at waterworks compared to chemically treated and non-disinfected systems. Furthermore, live/dead staining techniques and environmental scanning electron microscopy imaging revealed the presence of living and intact bacteria in biofilms on copper substrata. Cluster analyses of DGGE profiles demonstrated differences in the composition of biofilms on copper and steel materials.

Lasers use in dental implantology.

OBJECTIVE: The purpose of this literature review was to evaluate the present use of different laser systems in implant dentistry. MATERIALS AND METHODS: A literature search of MEDLINE-PubMed for articles published, describing the use of lasers in implant dentistry, was performed and articles were critically reviewed by the investigators to determine the strength of evidence. RESULTS: The literature review reveals a limited number of randomized clinical trials with regard to laser use in dentistry. Although many case studies indicate extensive use of lasers and promising results in dental implantology, lasers may be used for uncovering submerged implants atraumatically to prevent crestal bone loss, recontouring periimplant soft tissues and sculpting emergence profile for prosthetic components, raising surgical flaps, osseous recontouring, and creating parabolic tissue architecture. Additionally, bone harvesting of block grafts, window preparation in sinus lift procedures, ridge splitting, and debridement of extraction sockets for immediate implant placement were described. CONCLUSIONS: Aside from the many benefits associated with the use of lasers in implant-related procedures, there are also risks to consider from the laser irradiation on the implant surface and the periimplant tissues. Therefore, an appropriate training on laser use is mandatory to increase the clinical outcome and to control the potential of complications.

Diode laser offers minimal benefit for periodontal therapy.

Current evidence indicates that use of diode lasers in the treatment of periodontitis--either as a monotherapy or adjunctive to traditional therapy--offers minimal benefit. Further, subgingival application of the diode laser during nonsurgical periodontal therapy can result in undesired outcomes, even when using manufacturer-recommended parameters.

[Microbiological study of the efficiency of various hygienic products for toothbrushes].

Options vary about the microbial contamination of toothbrushes as well as selection of adequate remedies for their disinfection. A microbiological study of contamination of toothbrushes was conducted considering the efficiency of purifying tablets, ultraviolet radiation and 0.05% solution of chlorhexidine as means of toothbrushes disinfection.

Treatment of experimental periodontal disease with antimicrobial photodynamic therapy in nicotine-modified rats.

BACKGROUND: The aim of this study was to compare antimicrobial photodynamic therapy (aPDT) as an adjunctive treatment to scaling and root planing (SRP) for induced periodontitis in nicotine-modified rats. MATERIAL & METHODS: A total of 240 rats were evenly divided into two groups: C - saline solution treatment; N - nicotine treatment. Periodontal disease was induced in both groups at the first mandibular molar. After 7 days, the ligature was removed. All animals were submitted to SRP and were divided according to the following treatments: SRP - irrigation with saline solution; Toluidine Blue-O (TBO) - irrigation with phenothiazinium dye (100 µg/ml); LLLT - laser irradiation (660 nm; 0.03 W; 4 J); and aPDT - TBO and laser irradiation. Ten animals in each group/treatment were euthanized at 7, 15 and 30 days. The histometric and immunohistochemical values were statistically analysed. RESULTS: Intragroup analysis demonstrated that in both groups the aPDT treatment resulted in lower bone loss (BL) when compared to SRP in all experimental periods. Intergroup analysis demonstrated that aPDT treatment resulted in lower BL in Group N than in Group C treated with SRP in all experimental periods. CONCLUSION: Antimicrobial photodynamic therapy was an effective adjunctive treatment to SRP for induced periodontitis in nicotine-modified rats.

Study of the direct bactericidal effect of Nd:YAG and diode laser parameters used in endodontics on pigmented and nonpigmented bacteria.

Laser light can be used during endodontic procedures to sterilize the root canal by destroying bacteria. Previous in-vitro studies that investigated the mechanism of the destruction of bacteria inhabiting the root canal by 1,064-nm Nd:YAG and 808-nm diode laser light used substrates that absorb light in the near-infrared (NIR) spectrum. These substrates heat the bacterial microenvironment, which possibly contributes to cell death. To determine the direct effect of laser light on the bacterial sample in the absence of detrimental heating, a sapphire substrate, which is virtually transparent in NIR spectrum, was inoculated with bacterial samples and subjected to laser irradiation at 1,064 nm (1.5 W, 15 Hz) and at 808 nm (1.5 W, 20 Hz). Enterococcus faecalis, Escherichia coli, and Porphyromonas gingivalis bacteria were used. E. faecalis and E. coli were largely unaffected by laser light. The viability of P. gingivalis, a pigmented bacterium, was directly affected by both NIR wavelengths (a 57% decrease of viability at 1,064 nm and a 31% decrease at 808 nm). Our results indicate that the primary mediator of cell death appears to be the interaction between NIR laser light and the bacterial microenvironment, most likely in the form of heating. Our research suggests that when optimizing the efficacy of laser-assisted endodontic sterilization of the root canal, the optical characteristics of the bacterial microenvironment play a key role, as nonpigmented bacteria appear to be virtually transparent at 808 nm and 1,064 nm.