Application of 233 nm far-UVC LEDs for eradication of MRSA and MSSA and risk assessment on skin models.

A newly developed UVC LED source with an emission wavelength of 233 nm was proved on bactericidal efficacy and skin tolerability. The bactericidal efficacy was qualitatively analysed using blood agar test. Subsequently, quantitative analyses were performed on germ carrier tests using the MRSA strain DSM11822, the MSSA strain DSM799, S. epidermidis DSM1798 with various soil loads. Additionally, the compatibility of the germicidal radiation doses on excised human skin and reconstructed human epidermis was proved. Cell viability, DNA damage and production of radicals were assessed in comparison to typical UVC radiation from discharge lamps (222 nm, 254 nm) and UVB (280-380 nm) radiation for clinical assessment. At a dose of 40 mJ/cm2, the 233 nm light source reduced the viable microorganisms by a log10 reduction (LR) of 5 log10 levels if no soil load was present. Mucin and protein containing soil loads diminished the effect to an LR of 1.5-3.3. A salt solution representing artificial sweat (pH 8.4) had only minor effects on the reduction. The viability of the skin models was not reduced and the DNA damage was far below the damage evoked by 0.1 UVB minimal erythema dose, which can be regarded as safe. Furthermore, the induced damage vanished after 24 h. Irradiation on four consecutive days also did not evoke DNA damage. The radical formation was far lower than 20 min outdoor visible light would cause, which is classified as low radical load and can be compensated by the antioxidant defence system.

Effect of APTES modified TiO2 on antioxidant enzymes activity secreted by Escherichia coli and Staphylococcus epidermidis.

In this work, the impact of APTES-modified TiO2 photocatalysts on antioxidant enzymes (catalase and superoxide dismutase) activity secreted by bacteria was presented. Microbial tests has been examined using Escherichia coli (ATCC 29425) and Staphylococcus epidermidis (ATCC 49461) as model organisms. It was found that APTES-TiO2 affected the activity of antioxidant enzymes. Additionally, obtained APTES-TiO2 photocatalysts were capable of total E. coli and S. epidermidis inactivation under artificial solar light irradiation. The sample modified with the concentration of APTES equals 300 mM (TiO2-4h-120°C-300mM) showed the strongest photocatalytic activity toward both bacteria species. The two-stage photocatalytic mechanism of bacteria response to photocatalysts was proposed.

Carbon Nanomaterials and LED Irradiation as Antibacterial Strategies against Gram-Positive Multidrug-Resistant Pathogens.

BACKGROUND: Due to current antibiotic resistance worldwide, there is an urgent need to find new alternative antibacterial approaches capable of dealing with multidrug-resistant pathogens. Most recent studies have demonstrated the antibacterial activity and non-cytotoxicity of carbon nanomaterials such as graphene oxide (GO) and carbon nanofibers (CNFs). On the other hand, light-emitting diodes (LEDs) have shown great potential in a wide range of biomedical applications. METHODS: We investigated a nanotechnological strategy consisting of GO or CNFs combined with light-emitting diod (LED) irradiation as novel nanoweapons against two clinically relevant Gram-positive multidrug-resistant pathogens: methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). The cytotoxicity of GO and CNFs was studied in the presence of human keratinocyte HaCaT cells. RESULTS: GO or CNFs exhibited no cytotoxicity and high antibacterial activity in direct contact with MRSE and MRSA cells. Furthermore, when GO or CNFs were illuminated with LED light, the MRSE and MRSA cells lost viability. The rate of decrease in colony forming units from 0 to 3 h, measured per mL, increased to 98.5 ± 1.6% and 95.8 ± 1.4% for GO and 99.5 ± 0.6% and 99.7 ± 0.2% for CNFs. CONCLUSIONS: This combined antimicrobial approach opens up many biomedical research opportunities and provides an enhanced strategy for the prevention and treatment of Gram-positive multidrug-resistant infections.

In-depth analysis of antibacterial mechanisms of laser generated shockwave treatment.

Background and Objectives Laser generated shockwave (LGS) is a novel modality for minimally invasive disruption of bacterial biofilms. The objectives of this study are to determine the mechanisms behind LGS treatment and non-biofilm effects on bacterial disruption, including (1) comparing bacterial load with and without LGS in its planktonic form and (2) estimating bacterial cell permeability following LGS. Study Design/Materials and Methods For the first study, planktonic S. epidermidis were treated with gentamicin (0, 8, 16, 32, 64 µg/ml) with and without LGS (1064 nm Nd:YAG laser, 110.14 mJ/mm2 , pulse duration 9 ns, spot size 3 mm, n = 8/group), and absorbances at 600 nm compared. For the second study, four samples of planktonic S. epidermidis were treated with LGS (same settings). Propidium iodide (PI) uptake via flow cytometry as a measure of cell permeability was measured at 0, 10, and 20 minutes following LGS. RESULTS: In comparing corresponding gentamicin concentrations within both LGS-treated samples and controls at 0 hours, there were no differences in absorbance (P = 0.923 and P = 0.814, respectively). Flow cytometry found modest PI uptake (10.4 ± 2.5%) immediately following LGS treatment, with time-dependent increase and persistence of the signal at 20 minutes (R2 = 0.449, P = 0.048). CONCLUSION: Taken together, LGS does not appear to have direct bacteriocidal properties, but rather by allowing for biofilm disruption and bacterial cell membrane permeabilization, both of which likely increase topical antibiotic delivery to pathogenic organisms. Insight into the mechanisms of LGS will allow for improved clinical applications and facilitate safe and effective translation of this technology. Lasers Surg. Med. © 2018 Wiley Periodicals, Inc.

Decreased efficacy of UV inactivation of Staphylococcus aureus after multiple exposure and growth cycles.

UV disinfection is a relatively simple and cost-efficient disinfection method, especially for in-home greywater treatment. In this study, a bench scale experiment was performed using a LED collimated UV-C beam with a peak wavelength of 256 nm to determine if potentially pathogenic bacteria such as Staphylococcus aureus may become enriched in a semi-recirculating greywater system with UV as the sole disinfection step. A statistically significant (P < 0.001) decreasing trend in UV-C efficacy was observed between the 1st and 6th UV exposure-growth cycles of S. aureus (ATCC 25923), resulting in a 1.5 decrease in log10 removal (P < 0.00000) by the 5th iteration. An eleven-point dose-response curve of the 7th iteration of S. aureus was estimated and compared to the dose-response curve of the original strain; due to a longer apparent shoulder period and a decay constant of lesser degree, the dose required for a 4-log reduction of the enriched S. aureus was estimated to be ∼1.9 times greater (22.0 mJ⋅cm-2 versus 11.8 mJ⋅cm-2). However, experimental results with S. epidermidis (ATCC 12228) and two wild strains, S. aureus and S. warneri, exhibited no trend of increased resistance. UV doses exceeding 20 mJ⋅cm-2 are generally sufficient in achieving a 4-log reduction of bacteria in drinking water systems; however, the results exhibited in this study suggest that when recirculation is involved, there may be a need for UV doses exceeding what is necessary for a 4-log reduction to suppress the enrichment of strains which could pose a public health risk.

A pilot study on the disinfection efficacy of localized UV on the flushing-generated spread of pathogens.

The process of toilet-flushing can generate flushing-associated water droplets which can potentially expose humans to pathogen-laden aerosols. Very little is known about such aerosol dissemination or the means for minimizing exposure to these aerosols. This study has evaluated the efficacy of ultraviolet waveband C (UV-C) for disinfection of flushing-generated pathogen-laden aerosols through tests with localized disinfection systems for airborne and surface contaminations. Three types of bacteria were chosen for investigation: Staphylococcus epidermidis, Escherichia coli, and Salmonella typhimurium. Tests were conducted with UV-C tubes of 5 W and 10 W. High levels of disinfection efficacies were observed, ranging from 76% to 97% for bacteria-laden aerosols at sources of emission, and efficiencies of 53% to 79% for surface samples in localized systems. The results from the localized systems were further compared with those obtained with an upper-room ultraviolet germicidal irradiation (UVGI) system. As it is important to note, the UV-C doses and ozone emissions for the localized systems were found well below the limits recommended in current guidelines. This research has shown that the disinfection of flushing-generated pathogen-laden aerosols in proximity to the source of emission was more effective than at the more distant sites where aerosols may be dispersed to the environment.

Exploring photoinactivation of microbial biofilms using laser scanning microscopy and confined 2-photon excitation.

One pertinent complication in bacterial infection is the growth of biofilms, that is, communities of surface-adhered bacteria resilient to antibiotics. Photodynamic inactivation (PDI) has been proposed as an alternative to antibiotic treatment; however, novel techniques complementing standard efficacy measures are required. Herein, we present an approach employing multiphoton microscopy complemented with Airyscan super-resolution microscopy, to visualize the distribution of curcumin in Staphylococcus epidermidis biofilms. The effects of complexation of curcumin with hydroxypropyl-γ-cyclodextrin (HPγCD) were studied. It was shown that HPγCD curcumin demonstrated higher bioavailability in the biofilms compared to curcumin, without affecting the subcellular uptake. Spectral quantification following PDI demonstrates a method for monitoring elimination of biofilms in real time using noninvasive 3D imaging. Additionally, spatially confined 2-photon inactivation was demonstrated for the first time in biofilms. These results support the feasibility of advanced optical microscopy as a sensitive tool for evaluating treatment efficacy in biofilms toward improved mechanistic studies of PDI.

The synergistic bactericidal effect of vancomycin on UTMD treated biofilm involves damage to bacterial cells and enhancement of metabolic activities.

In this study, the synergistic effect of vancomycin, a cell wall synthesis inhibitor, and ultrasound-targeted microbubble destruction (UTMD), on cell viability of Staphylococcus epidermidis, embedded in biofilm, was investigated. Biofilms are the leading causes of antibiotic-resistant bacterial infections of medical implants and prosthetics worldwide. The antibiotic-resistant nature of biofilm-embedded pathogens poses a critical challenge to the medical community. Previously, studies have demonstrated the efficacy of using ultrasound waves and UTMD in circumventing this problem. However, the mechanism(s) underlying this phenomenon was not clear. Here, the present study showed that both ultrasound and UTMD damaged the cell wall structure of S. epidermidis, and floccules and fragments from damaged cells were observed on transmission electron microscope micrograph. However, the cell membrane integrity was not seriously affected by treatments, and the treatment increased the metabolic activity levels of the dormant biofilm-embedded bacteria, detected by confocal laser scanning microscope and flow cytometry, which could make them susceptible to the effect of the antibiotic. Thus, the biological mechanism underlying the efficacy of the combined treatment involving UTMD and vancomycin in the case of S. epidermidis biofilm was dissected, which may be utilized for further investigations on other biofilm pathogens before clinical use.

Vitamin K5 is an efficient photosensitizer for ultraviolet A light inactivation of bacteria.

Photodynamic treatment combining light and a photosensitizer molecule can be an effective method to inactivate pathogenic bacteria. This study identified vitamin K5 as an efficient photosensitizer for ultraviolet light A (UVA)-induced bacterial inactivation. Six bacterial species, Bacillus cereus (vegetative form), Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Klebsiella pneumoniae, and two species of antibiotic-resistant bacteria, Pseudomonas aeruginosa* and Staphylococcus aureus*, were suspended in aqueous solutions with or without vitamin K5 and exposed to UVA irradiation. UVA irradiation (5.8 J cm-2) with vitamin K5 (1600 µmol l-1) reduced the colony forming units (CFU) of these bacteria by three to seven logs. Antibiotic resistant bacteria were also susceptible to the bactericidal effects of UVA and vitamin K5 combination treatment. Inactivation of bacteria in human plasma required higher doses of UVA light and vitamin K5. UVA irradiation (30 J cm-2) with vitamin K5 (2000 µmol l-1) reduced E. coli and S. aureus spiked into human plasma by seven logs CFU/ml. Reactive oxygen species, such as superoxide anion radicals and hydroxyl radicals, were found to be generated in vitamin K5 aqueous solution after UVA irradiation, suggesting these oxygen species may mediate the inactivation of the bacteria.

Effect of ultrasonic irradiation on bacterial biofilms.

PURPOSE: The purpose of this study was to clarify the effect of ultrasonic irradiation on biofilm produced by Staphylococcus epidermidis (S. epidermidis), which causes central venous catheter-related infections. MATERIALS AND METHODS: Staphylococcus epidermidis (S. epidermidis, ATCC 35984 RP 62A) was used in this study. First, biofilm was prepared from S. epidermidis on the bottom of the upper left well of a 6-well plate. Next, the biofilm was irradiated for 24 h with 1-MHz ultrasound (US) in the continuous wave mode to serve as the US irradiation group. The acoustic power irradiated below the bottom of the well was 3.8 mW. As a control (non-US irradiation group), non-irradiated biofilm on the bottom of a 6-well plate was incubated at 37 °C in an atmosphere of 5.0% CO2. After US irradiation, the bottoms of the wells were stained with 0.1% crystal violet for 60 s. To extract the crystal violet, 99.5% ethanol was added to the wells, and the extracted solutions were measured at an absorbance of 595 nm. RESULT: The absorbance of the US irradiation group was significantly less than that of the non-US irradiation group (p < 0.01). CONCLUSION: US irradiation can decrease the amount of S. epidermidis biofilm when the duration of US irradiation is sufficiently long even if the acoustic intensity is low.

The response of human bacteria to static magnetic field and radiofrequency electromagnetic field.

Cell phones and electronic appliances and devices are inseparable from most people in modern society and the electromagnetic field (EMF) from the devices is a potential health threat. Although the direct health effect of a cell phone and its radiofrequency (RF) EMF to human is still elusive, the effect to unicellular organisms is rather apparent. Human microbiota, including skin microbiota, has been linked to a very significant role in the health of a host human body. It is important to understand the response of human skin microbiota to the RF-EMF from cell phones and personal electronic devices, since this may be one of the potential mechanisms of a human health threat brought about by the disruption of the intimate and balanced host-microbiota relationship. Here, we investigated the response of both laboratory culture strains and isolates of skin bacteria under static magnetic field (SMF) and RF-EMF. The growth patterns of laboratory cultures of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus epidermidis under SMF were variable per different species. The bacterial isolates of skin microbiota from 4 subjects with different cell phone usage history also showed inconsistent growth responses. These findings led us to hypothesize that cell phone level RF-EMF disrupts human skin microbiota. Thus, the results from the current study lay ground for more comprehensive research on the effect of RF-EMF on human health through the human-microbiota relationship.

The uses and limitations of a hand-held germicidal ultraviolet wand for surface disinfection.

The morbidity and mortality from healthcare associated infections has raised concern that conventional disinfection methods are inadequate and that other adjunct methods such as room fumigation and ultraviolet irradiation may be needed. There is also concern that these alternative methods may pose a risk to workers and patients. OBJECTIVES: (1) Determine the efficacy of a germicidal UV-C wand for surface disinfection, (2) evaluate changing relative humidity (RH) and different target distances on bacteria kill rates, and (3) assess potential exposure concerns. METHODS: This study investigates whether a hand-held germicidal wand can efficaciously disinfect surfaces treated with either a vegetative or spore forming bacterium and to evaluate the effect of changing environmental conditions such as relative humidity (RH), target position, and target distances on microbial kill rates. RESULTS: Kill rate was best at 40-65% RH at a temperature range of 21-24°C. Both high and low RH interfered with the ability of UV-C to kill the vegetative microbe. In the case of the spore forming bacterium, increased surface drying time was the most significant factor increasing kill rate. CONCLUSIONS: This research demonstrates that UV-C was efficacious under optimal conditions, a direct beam exposure, and a short target distance (12.7 cm). However, there are limitations when used in non-optimal conditions. Increased distance and indirect beam angles resulted in lower kill rates. It is also important to minimize unnecessary patient and worker exposure during its use.

Efficiency of riboflavin and ultraviolet light treatment against high levels of biofilm-derived Staphylococcus epidermidis in buffy coat platelet concentrates.

BACKGROUND AND OBJECTIVES: Staphylococcus epidermidis forms surface-attached aggregates (biofilms) in platelet concentrates (PCs), which are linked to missed detection during PC screening. This study was aimed at evaluating the efficacy of riboflavin-UV treatment to inactivate S. epidermidis biofilms in buffy coat (BC) PCs. MATERIALS AND METHODS: Biofilm and non-biofilm cells from S. epidermidis ST-10002 and S. epidermidis AZ-66 were individually inoculated into whole blood (WB) units (~106 colony-forming units (CFU)/ml) (N = 4-5). One spiked and three unspiked WB units were processed to produce a BC-PC pool. Riboflavin was added to the pool which was then split into two bags: one for UV treatment and the second was untreated. Bacterial counts were determined before and after treatment. In vitro PC quality was assessed by flow cytometry and dynamic light scattering. RESULTS: Bacterial counts were reduced during BC-PC production from ~106 CFU/ml in WB to 103 -104 CFU/ml in PCs (P < 0·0001). Riboflavin-UV treatment resulted in significantly higher reduction of S. epidermidis AZ-66 than strain ST-10002 (≥3·5 log reduction and 2·6-2·8 log reduction, respectively, P < 0·0001). Remaining bacteria post-treatment were able to proliferate in PCs. No differences in S. epidermidis inactivation were observed in PCs produced from WB inoculated with biofilm or non-biofilm cells (P > 0·05). Platelet activation was enhanced in PCs produced with WB inoculated with biofilms compared to non-biofilm cells (P < 0·05). CONCLUSION: Riboflavin-UV treatment was similarly efficacious in PCs produced from WB inoculated with S. epidermidis biofilm or non-biofilm cells. Levels of biofilm-derived S. epidermidis ≥103 CFU/ml were not completely inactivated; however, further testing is necessary with lower (real-life) bacterial levels.

Laser-generated shockwaves enhance antibacterial activity against biofilms in vitro.

BACKGROUND AND OBJECTIVES: Bacterial biofilm formation within chronic wound beds, which provides an effective barrier against antibiotics, is a known cause of recalcitrant infections and a significant healthcare burden, often requiring repeated surgical debridements. Laser-generated shockwaves (LGS) is a novel, minimally invasive, and nonthermal modality for biofilm mechanical debridement which utilizes compressive stress waves, generated by photonic absorption in thin titanium films to mechanically disrupt the biofilm. Prior studies have demonstrated LGS monotherapy to be selectively efficacious for biofilm disruption and safe for host tissues. In this study, we sought to determine if LGS can enhance the antimicrobial activity and biofilm disruption capability of topical antibiotic therapy. STUDY DESIGN/MATERIALS AND METHODS: Staphylococcus epidermidis biofilms grown in vitro on glass were treated with topical gentamicin (31, 62, and 124 µg/ml) with and without LGS (n = 3-11/treatment group). Mechanical shockwaves were generated with a 1,064 nm Nd:YAG laser (laser fluence 110.14 mJ/mm2 , pulse duration 5 ns, spot size 3 mm). Following a 24-hour incubation period, bacterial viability was assessed by determining the number of colony-forming units (CFU) via the Miles and Misra method. Residual biofilm bioburden was analyzed using the crystal violet biofilm assay. RESULTS: With gentamicin monotherapy, CFU density (CFU/mm2 ) at 31, 62, and 124 µg/ml were (282 ± 84) × 104 , (185 ± 34) × 104 , and (113 ± 9) × 104 , respectively. With LGS and gentamicin therapy, CFU density decreased to (170 ± 44) × 104 , (89 ± 24) × 104 , and (43 ± 3) × 104 , respectively (P = 0.1704, 0.0302, and 0.0004 when compared with gentamicin alone). Biofilm burden as measured by the assay in the gentamicin 31, 62, and 124 µg/ml groups was reduced by 80%, 95%, and 98% when LGS was added (P = 0.0102, >0.0001, and 0.0001 for all groups when compared with gentamicin alone). Furthermore, samples treated with LGS saw an increase in susceptibility to gentamicin, in terms of reduced biofilm bioburden and CFU densities. CONCLUSION: LGS enhances the efficacy of topical antibiotics in an in vitro model. This has significant implications for clinical applications in the management of chronic soft tissue infections and recalcitrant chronic rhinosinusitis. Lasers Surg. Med. 49:539-547, 2017. © 2017 Wiley Periodicals, Inc.

Chlorin e6-Mediated Photodynamic Therapy Suppresses P. acnes-Induced Inflammatory Response via NFκB and MAPKs Signaling Pathway.

Photodynamic therapy (PDT), consisting of photosensitizer, light, and oxygen has been used for the treatment of various diseases including cancers, microbial infections and skin disorders. In this study, we examined the anti-inflammatory effect of chlorin e6-mediated PDT in P. acnes-infected HaCaT cells using photosensitizer chlorin e6 (Ce6) and halogen light. The live and heat-killed P. acnes triggered an upregulation of inflammatory molecules such as iNOS, NO, and inflammatory cytokine in HaCaT cells and mouse model. Ce6-mediated PDT notably downregulated the expression of these inflammatory molecules in vitro and in vivo. Similarly, chlorin e6-mediated PDT was capable of regulating inflammatory response in both live and heat killed S. epidermidis exposed HaCaT cells. Moreover, phosphorylation of p38, JNK, and ERK were reduced by Ce6-mediated PDT. Ce6-mediated PDT also reduced the phosphorylation of IKKα/ß, IĸBα and NFκB p65 in P. acnes-stimulated HaCaT cells. In addition, the dramatic increase in the nuclear translocation of NFκB p65 observed upon stimulation with P. acnes was markedly impaired by Ce6-based PDT. This is the first suggestion that Ce6-mediated PDT suppresses P. acnes-induced inflammation through modulating NFκB and MAPKs signaling pathways.

Interaction of Staphylococci with Human B cells.

Staphylococcus aureus is a leading cause of human infections worldwide. The pathogen produces numerous molecules that can interfere with recognition and binding by host innate immune cells, an initial step required for the ingestion and subsequent destruction of microbes by phagocytes. To better understand the interaction of this pathogen with human immune cells, we compared the association of S. aureus and S. epidermidis with leukocytes in human blood. We found that a significantly greater proportion of B cells associated with S. epidermidis relative to S. aureus. Complement components and complement receptors were important for the binding of B cells with S. epidermidis. Experiments using staphylococci inactivated by ultraviolet radiation and S. aureus isogenic deletion mutants indicated that S. aureus secretes molecules regulated by the SaeR/S two-component system that interfere with the ability of human B cells to bind this bacterium. We hypothesize that the relative inability of B cells to bind S. aureus contributes to the microbe's success as a human pathogen.

Cytotoxic responses to 405nm light exposure in mammalian and bacterial cells: Involvement of reactive oxygen species.

Light at wavelength 405 nm is an effective bactericide. Previous studies showed that exposing mammalian cells to 405 nm light at 36 J/cm(2) (a bactericidal dose) had no significant effect on normal cell function, although at higher doses (54 J/cm(2)), mammalian cell death became evident. This research demonstrates that mammalian and bacterial cell toxicity induced by 405 nm light exposure is accompanied by reactive oxygen species production, as detected by generation of fluorescence from 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate. As indicators of the resulting oxidative stress in mammalian cells, a decrease in intracellular reduced glutathione content and a corresponding increase in the efflux of oxidised glutathione were observed from 405 nm light treated cells. The mammalian cells were significantly protected from dying at 54 J/cm(2) in the presence of catalase, which detoxifies H2O2. Bacterial cells were significantly protected by sodium pyruvate (H2O2 scavenger) and by a combination of free radical scavengers (sodium pyruvate, dimethyl thiourea (OH scavenger) and catalase) at 162 and 324 J/cm(2). Results therefore suggested that the cytotoxic mechanism of 405 nm light in mammalian cells and bacteria could be oxidative stress involving predominantly H2O2 generation, with other ROS contributing to the damage.

Photodynamic UVA-riboflavin bacterial elimination in antibiotic-resistant bacteria.

BACKGROUND: To evaluate the bactericidal effect of clinical ultraviolet A (UVA) settings used in photoactivated chromophore for infectious keratitis (PACK)-collagen cross-linking (CXL) in antibiotic-resistant and non-resistant bacterial strains. METHODS: Well-characterized bacterial strains from clinical isolates, without and with antibiotic resistance, were studied in a pairwise comparison. The evaluated pathogens were Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis. Bacteria were dispersed in PBS and diluted to a concentration of approximately 4 × 105 /ml. Riboflavin was added to a concentration of 0.01%. By spreading the solution on a microscope slide, a fluid film layer, with a thickness of around 400 mm, was formed and UVA exposure followed. Eight separate exposures were made for each strain (n = 8). The degree of elimination in resistant and non-resistant pathogens was compared. RESULTS: The bactericidal efficacy of exposure differed between the tested microorganisms, and the mean elimination ranged between 60 and 92%, being most extensive in both of the evaluated Pseudomonas strains and least in the E. faecalis strains. Similar reductions were seen in antibiotic-resistant and non-resistant strains, with the exception of S. aureus, in which the resistant strain metchicillin-resistant Staphylococcus aureus (MRSA) was eradicated in a greater extent than the non-resistant strain (P = 0.030). CONCLUSION: UVA-riboflavin settings used in PACK-CXL are effective in reducing both antibiotic-resistant and non-resistant bacteria. Antibiotic resistance does not appear to be protective against the photooxidative exposure.

In vitro antibacterial properties and UV induced response from Staphylococcus epidermidis on Ag/Ti oxide thin films.

Implanted materials are susceptible to bacterial colonization and biofilm formation, which can result in severe infection and lost implant function. UV induced photocatalytic disinfection on TiO2 and release of Ag(+) ions are two promising strategies to combat such events, and can be combined for improved efficiency. In the current study, a combinatorial physical vapor deposition technique was utilized to construct a gradient coating between Ag and Ti oxide, and the coating was evaluated for antibacterial properties in darkness and under UV light against Staphylococcus epidermidis. The findings revealed a potent antibacterial effect in darkness due to Ag(+) release, with near full elimination (97%) of viable bacteria and visible cell lysis on Ag dominated surfaces. The photocatalytic activity, however, was demonstrated poor due to low TiO2 crystallinity, and UV light irradiation of the coating did not contribute to the antibacterial effect. On the contrary, bacterial viability was in several instances higher after UV illumination, proposing a UV induced SOS response from the bacteria that limited the reduction rate during Ag(+) exposure. Such secondary effects should thus be considered in the development of multifunctional coatings that rely on UV activation.

Cationic Oligo(thiophene ethynylene) with Broad-Spectrum and High Antibacterial Efficiency under White Light and Specific Biocidal Activity against S. aureus in Dark.

We designed and synthesized a novel oligo(thiophene ethynylene) (OTE) to investigate the antibacterial activities against Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Ralstonia solanacearum and Escherichia coli) bacteria in vitro by photodynamic therapy (PDT). Notably, OTE presents broad-spectrum and greatly high antibacterial activities after white light irradiation at nanogram per milliliter concentrations. The half inhibitory concentrations (IC50) values obtained for S. aureus, S. epidermidis, E. coli, and R. solanacearum are 8, 13, 24, and 52 ng/mL after illumination for 30 min, respectively, which are lower than that of other PDT agents. Interestingly, OTE shows the specific and very strong dark killing capability against S. aureus at the concentration of 180 ng/mL for 30 min, which is the highest efficiency biocide against S. aureus without the need of irradiation to date. The antibacterial mechanism investigated demonstrated that reactive oxygen species or singlet-oxygen generated by OTE kills bacteria irreversibly upon white light irradiation, and OTE as a v-type oligomer exerts its toxicity directly on destroying bacterial cytoplasmic membrane in the dark. Importantly, the OTE shows no cell cytotoxicity and excellent biocompatibility. The results indicate that it is potential to provide versatile applications in the efficient control of pathogenic organisms and specific application for killing S. aureus.