Evaluation of photocatalysis inactivation in indoor air purification of pathogenic microbes by using the different nanomaterials based on TiO2 nanomaterials.

The photocatalytic technology for indoor air disinfection has been broadly studied in the last decade. Selecting proper photocatalysts with high disinfection efficiency remains to be a challenge. By doping with the incorporation of metals, the bandgap can be narrowed while avoiding the recombination of photogenerated charge. Three photocatalysts (Ag-TiO2, MnO2-TiO2, and MnS2-TiO2) were tested in photocatalytic sterilization process. The results revealed that Ag-TiO2 had the best antibacterial performance. Within 20 min, the concentration of Serratia marcescens (the tested bacteria) decreased log number of ln 4.04 under 640 w/m2 light intensity with 1000 µg/mL of Ag-TiO2. During the process of inactivating bacteria, the cell membranes of bacterial was destructed and thus decreasing the activity of enzymes and releasing the cell contents, due to the generation of reactive oxygen species (O2•- and •OH) and thermal effect. Spectral regulation has the greatest impact on the sterilization efficiency of MnO2-TiO2, which reduces the probability of photocatalytic materials being excited.

Photodynamic inactivation diminishes quorum sensing-mediated virulence factor production and biofilm formation of Serratia marcescens.

Serratia marcescens is an opportunistic human pathogen causing nosocomial infections and displays expanded resistance towards the conventional antibiotics. In S. marcescens, quorum sensing (QS) mechanism coordinates the population-dependent behaviors and regulates the virulence factors production. Photodynamic inactivation (PDI) is a promising alternative for the treatment of infections caused by drug resistant bacteria. Although PDI should be applied at lethal doses, it is possible that during PDI treatment, pathogens encounter sub-lethal doses of PDI (sPDI). sPDI cannot kill microorganisms, but it can considerably influence the microbial virulence. So, in this study, the effect of methylene blue (MB)-mediated PDI on QS-mediated virulence factor production and biofilm formation of S. marcescens at lethal and sub-lethal doses was evaluated. The biofilm formation and virulence factor production of S. marcescens ATCC 13,880 and S. marcescens Sm2 were assessed before and after PDI treatment. Besides, the effect of lethal and sub-lethal PDI on expression of bsmA and bsmB (Biofilm maturation), fimA and fimC (Major fimbrial protein), flhD (Regulator of flagellar mediated swarming and swimming motility) and swrR (AHL-dependent regulator) genes were evaluated by quantitative real time polymerase chain reaction. Lethal and sub-lethal PDI resulted in a significant decrease in biofilm formation, swimming/swarming motility, and pigment and hemolysin production ability of S. marcescens strains. bsmA, bsmB, flhD and swrR genes were down-regulated after PDI treatments. In conclusion, QS-mediated virulence factor production and biofilm formation ability of the two studied S. marcescens strains decreased after both lethal and sub-lethal PDI.

Bacterial biophotons as non-local information carriers: Species-specific spectral characteristics of a stress response.

Studies by Alexander Gurwitsch in the 1920' s with onion root cells revealed the phenomenon of mitogenetic radiation. Subsequent works by Popp, Van Wijk, Quickenden, Tillbury, and Trushin have demonstrated a link between Gurwitsch's mitogenetic radiation and the biophoton, emissions of light correlated with biological processes. The present study seeks to expand upon these and other works to explore whether biophoton emissions of bacterial cultures is used as an information carrier of environmental stress. Bacterial cultures (Escherichia coli and Serratia marcescens) were incubated for 24 hr in 5 ml of nutrient broth to stationary phase and cell densities of ~107 cells/mL. Cultures of E. coli were placed upon a photomultiplier tube housed within a dark box. A second bacterial culture, either E. coli or S. marcescens, was placed in an identical dark box at a distance of 5 m and received injections of hydrogen peroxide. Spectral analyses revealed significant differences in peak frequencies of 7.2, 10.1, and 24.9 Hz in the amplitude modulation of the emitted biophoton signal with respect to whether a peroxide injection occurred or not, and whether the species receiving the injection was E. coli or S. marcescens. These and the subsequent results of discriminant functions suggest that bacteria may release biophotons as a non-local communication system in response to stress, and that these biophotons are species specific.

The propagation of active-passive interfaces in bacterial swarms.

Propagating interfaces are ubiquitous in nature, underlying instabilities and pattern formation in biology and material science. Physical principles governing interface growth are well understood in passive settings; however, our understanding of interfaces in active systems is still in its infancy. Here, we study the evolution of an active-passive interface using a model active matter system, bacterial swarms. We use ultra-violet light exposure to create compact domains of passive bacteria within Serratia marcescens swarms, thereby creating interfaces separating motile and immotile cells. Post-exposure, the boundary re-shapes and erodes due to self-emergent collective flows. We demonstrate that the active-passive boundary acts as a diffuse interface with mechanical properties set by the flow. Intriguingly, interfacial velocity couples to local swarm speed and interface curvature, raising the possibility that an active analogue to classic Gibbs-Thomson-Stefan conditions may control this boundary propagation.

Bactericidal effects of deep ultraviolet light-emitting diode for solutions during intravenous infusion.

Background: Ultraviolet irradiation is effectively used as a disinfection method for inactivating microorganisms. Methods: We investigated the bactericidal effects by irradiation with a deep-ultraviolet light-emitting diode (DUV-LED) on the causative microorganisms of catheter related blood stream infection contaminating the solution for intravenous infusion. For irradiation, prototype modules for water disinfection with a DUV-LED were used. Experiments were conducted on five kinds of microorganisms. We examined the dependence of bactericidal action on eleven solutions. Administration sets were carried out three types. Results: When the administration set JY-PB343L containing the infusion tube made of polybutadiene was used, the bactericidal action of the DUV-LED against all tested microorganisms in the physiological saline solutions was considered to be effective. We confirmed that the number of viable bacteria decreased in 5% glucose solution and electrolyte infusions with DUV-LED irradiation. Conclusions: These results indicate that the DUV-LED irradiation has bactericidal effects in glucose infusion and electrolyte infusions by irradiating via a plasticizer-free polybutadiene administration set. We consider DUV-LED irradiation to be clinically applicable.

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.

Bacterial growth rates are influenced by cellular characteristics of individual species when immersed in electromagnetic fields.

Previous studies have shown that exposure to extremely low-frequency electromagnetic fields (ELF-EMFs) have negative effects on the rate of growth of bacteria. In the present study, two Gram-positive and two Gram-negative species were exposed to six magnetic field conditions in broth cultures. Three variations of the 'Thomas' pulsed frequency-modulated pattern; a strong-static "puck" magnet upwards of 5000G in intensity; a pair of these magnets rotating opposite one another at ∼30rpm; and finally a strong dynamic magnetic field generator termed the 'Resonator' with an average intensity of 250µT were used. Growth rate was discerned by optical density (OD) measurements every hour at 600nm. ELF-EMF conditions significantly affected the rates of growth of the bacterial cultures, while the two static magnetic field conditions were not statistically significant. Most interestingly, the 'Resonator' dynamic magnetic field increased the rates of growth of three species (Staphylococcus epidermidis, Staphylococcus aureus, and Escherichia coli), while slowing the growth of one (Serratia marcescens). We suggest that these effects are due to individual biophysical characteristics of the bacterial species.

Minimizing the exposure of airborne pathogens by upper-room ultraviolet germicidal irradiation: an experimental and numerical study.

There has been increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) because of its proven effectiveness in disinfecting airborne pathogens. An improved drift flux mathematical model is developed for optimizing the design of indoor upper-room UVGI systems by predicting the distribution and inactivation of bioaerosols in a ventilation room equipped with a UVGI system. The model takes into account several bacteria removal mechanisms such as convection, turbulent diffusion, deposition and UV inactivation. Before applying the model, the natural die-off rate and susceptibility constants of bioaerosols were measured experimentally. Two bacteria aerosols, Escherichia coli and Serratia marcescens, were tested for this purpose. It was found out that the general decay trend of the bioaerosol concentration predicted by the numerical model agrees well with the experimental measurements. The modelling results agree better with experimental observations for the case when the UVGI inactivation mechanism dominates at the upper-room region than for the case without UVGI. The numerical results also illustrate that the spatial distribution of airborne bacteria was influenced by both air-flow pattern and irradiance distribution. In addition to predicting the local variation of concentration, the model assesses the overall performance of an upper-room UVGI system. This model has great potential for optimizing the design of indoor an upper-room UVGI systems.

Biogenesis of outer membrane vesicles in Serratia marcescens is thermoregulated and can be induced by activation of the Rcs phosphorelay system.

Outer membrane vesicles (OMVs) have been identified in a wide range of bacteria, yet little is known of their biogenesis. It has been proposed that OMVs can act as long-range toxin delivery vectors and as a novel stress response. We have found that the formation of OMVs in the gram-negative opportunistic pathogen Serratia marcescens is thermoregulated, with a significant amount of OMVs produced at 22 or 30°C and negligible quantities formed at 37°C under laboratory conditions. Inactivation of the synthesis of the enterobacterial common antigen (ECA) resulted in a hypervesiculation phenotype, supporting the hypothesis that OMVs are produced in response to stress. We demonstrate that the phenotype can be reversed to wild-type (WT) levels upon the loss of the Rcs phosphorelay response regulator RcsB, but not RcsA, suggesting a role for the Rcs phosphorelay in the production of OMVs. MS fingerprinting of the OMVs provided evidence of cargo selection within wild-type cells, suggesting a possible role for Serratia OMVs in toxin delivery. In addition, OMV-associated cargo proved toxic upon injection into the haemocoel of Galleria mellonella larvae. These experiments demonstrate that OMVs are the result of a regulated process in Serratia and suggest that OMVs could play a role in virulence.

Response of pigmented Serratia marcescens to the illumination.

Variations in the illumination conditions (light/darkness) affected both the biosynthesis of prodigiosin and energy metabolism of the pigmented strain ATCC 9986 Serratia marcescens growing aerobical in the batch culture were shown. In the process incubation the transition of the pigmented culture from illumination within (24 h, 48 h) in the dark conditions increased the prodigiosin synthesis by 2.0, 2.5 times, respectively. At the same time, the illumination did not influence the prodigiosin biosynthesis in the stationary growth phase. In the initial period of prodigiosin synthesis the rate of oxygen consumption was higher than later when the pigment synthesis gradually decreased. The respiration activity of colorless strain 24-5 is not independent from the lighting conditions. The regulation of energetic pathways in the light and in darkness has been revealed. Prodigiosin is associated with the hydrophobic protein and it is represented pigment protein complex by diameter of particles less 100 kDa. Fluorescence spectrum of prodigiosin and it the absorption spectra of derivatives of high orders D(IV) and D(VIII) were described.

Removal of Serratia marcescens aerosols using an electrostatic precipitator.

We characterized the efficacy of an electrostatic precipitator (ESP) air-cleaner in reducing the concentration of Serratia marcescens in an enclosed space. We used an experimental room (4.5 x 3 x 2.9 m) in which electrostatic aircleaners were located. Two air-cleaners enhanced the equivalent ventilation rates in the chamber by about 3.3 air changes per hour (ACH) over the 2 ACH provided by the mechanical ventilation system. Natural die-off of the organisms provided an additional equivalent of 3 ACH, so that the total ventilation rate with the ESP air-cleaners was 8.3 ACH. We also examined whether the ESP air-cleaners altered the deposition of Serratia marcescens aerosols on the experimental room surfaces. We did not find any significant differences in the number of colony forming units recovered from surfaces with and without the air-cleaners. We installed UV lights inside the ESPs and determined if UV light, in addition to electrical fields, increased the efficacy of the ESPs. The presence of UV light inside the ESP reduced S. marcescens aerosols by approximately 2 ACH. Finally, a box model indicates that the efficiency of the air-cleaner increases for both biological and nonbiological particles at ventilation rates of 0.2-1, which are typical for residential settings.

Diverse responses to UV-B radiation and repair mechanisms of bacteria isolated from high-altitude aquatic environments.

Acinetobacter johnsonii A2 isolated from the natural community of Laguna Azul (Andean Mountains at 4,560 m above sea level), Serratia marcescens MF42, Pseudomonas sp. strain MF8 isolated from the planktonic community, and Cytophaga sp. strain MF7 isolated from the benthic community from Laguna Pozuelos (Andean Puna at 3,600 m above sea level) were subjected to UV-B (3,931 J m-2) irradiation. In addition, a marine Pseudomonas putida strain, 2IDINH, and a second Acinetobacter johnsonii strain, ATCC 17909, were used as external controls. Resistance to UV-B and kinetic rates of light-dependent (UV-A [315 to 400 nm] and cool white light [400 to 700 nm]) and -independent reactivation following exposure were determined by measuring the survival (expressed as CFU) and accumulation of cyclobutane pyrimidine dimers (CPD). Significant differences in survival after UV-B irradiation were observed: Acinetobacter johnsonii A2, 48%; Acinetobacter johnsonii ATCC 17909, 20%; Pseudomonas sp. strain MF8, 40%; marine Pseudomonas putida strain 2IDINH, 12%; Cytophaga sp. strain MF7, 20%; and Serratia marcescens, 21%. Most bacteria exhibited little DNA damage (between 40 and 80 CPD/Mb), except for the benthic isolate Cytophaga sp. strain MF7 (400 CPD/Mb) and Acinetobacter johnsonii ATCC 17909 (160 CPD/Mb). The recovery strategies through dark and light repair were different in all strains. The most efficient in recovering were both Acinetobacter johnsonii A2 and Cytophaga sp. strain MF7; Serratia marcescens MF42 showed intermediate recovery, and in both Pseudomonas strains, recovery was essentially zero. The UV-B responses and recovery abilities of the different bacteria were consistent with the irradiation levels in their native environment.

Size and UV germicidal irradiation susceptibility of Serratia marcescens when aerosolized from different suspending media.

Experimental systems have been built in laboratories worldwide to investigate the influence of various environmental parameters on the efficacy of UV germicidal irradiation (UVGI) for deactivating airborne microorganisms. It is generally recognized that data from different laboratories might vary significantly due to differences in systems and experimental conditions. In this study we looked at the effect of the composition of the suspending medium on the size and UVGI susceptibility of Serratia marcescens in an experimental system built in our laboratory. S. marcescens was suspended in (i) distilled water, (ii) phosphate buffer, (iii) 10% fetal calf serum, (iv) phosphate-buffered saline (saline, 0.8% sodium chloride), and (v) synthetic saliva (phosphate-buffered saline with 10% fetal calf serum). At low humidity (36%), S. marcescens suspended in water-only medium was the most susceptible to UVGI, followed by those in serum-only medium. The count median diameters (CMDs) for culturable particles from water-only and serum-only media were 0.88 and 0.95 micro m, respectively, with the measurements based on their aerodynamic behavior. The bacteria suspended in phosphate buffer, synthetic saliva, and phosphate-buffered saline had similar UVGI susceptibility and CMD at 1.0, 1.4, and 1.5 micro m, respectively. At high humidity (68%) the CMD of the particles increased by 6 to 16%, and at the same time UVGI susceptibility decreased, with the magnitude of decrease related to the type of suspending medium. In conclusion, the choice of suspending medium influenced both size and UVGI susceptibility of S. marcescens. These data are valuable for making comparisons and deciding on the use of an appropriate medium for various applications.

Rapid immunoassays for detection of UV-induced cyclobutane pyrimidine dimers in whole bacterial cells.

Immunoassays were developed to measure DNA damage retained by UV-irradiated whole bacterial cells. Active Mycobacterium parafortuitum and Serratia marcescens cells were fixed and incubated with cyclobutane pyrimidine dimer-binding antibodies after being exposed to known UV doses (254 nm). When both fluorescent (Alexa Fluor 488) and radiolabeled ((125)I) secondary antibodies were used as reporters, indirect whole-cell assays were sensitive enough to measure intracellular UV photoproducts in M. parafortuitum and S. marcescens cells as well as photoenzymatic repair responses in S. marcescens cells. For the same UV dose, fluorescent DNA photoproduct detection limits in whole-cell assays (immunofluorescent microscopy) were similar to those in fluorescent assays performed on membrane-bound DNA extracts (immunoslot blot). With either fluorescent or radiolabeled reporters, the intracellular cyclobutane pyrimidine dimer content of UV-irradiated whole bacterial cells could be reliably quantified after undergoing a <0.5-order-of-magnitude decrease in culturability. Immunofluorescent microscopy results showed that photoenzymatic repair competence is not uniformly distributed among exponential-growth UV-irradiated pure cultures.

Influence of relative humidity on particle size and UV sensitivity of Serratia marcescens and Mycobacterium bovis BCG aerosols.

SETTING: A study of Serratia marcescens and BCG aerosols. OBJECTIVE: To evaluate the effect of relative humidity (RH) on (1) the particle size and (2) sensitivity of 254nm germicidal ultraviolet (UV) irradiation. METHODS: We built a RH controlled experimental chamber into which bacteria were aerosolized, exposed to varying amounts of UV irradiance over measured time periods, and quantitatively evaluated for viability. Aerosolized Serratia marcescens and bacille Calmette-Guérin (BCG) were subject to UV doses ranging from 57-829 microW. sec/cm(2), and sampled with a six-stage Andersen culture plate impactor at RHs ranging from 25-95%. RESULTS: Percent survival for both organisms was inversely related to UV dose. Serratia marcescens was more susceptible to UV than BCG under all conditions. More than 95% of the bacterial aerosol particles were 1.1-4.7 microm in aerodynamic diameter, and particles sizes increased from low (25-36%) to high (85-95%) RH. The count median diameter ranged from 1.9-2.6 microm for Serratia marcescens and from 2.2-2.7 microm for BCG as RH increased. For both Serratia marcescens and BCG, resistance to UV increased as RH increased. The UV resistance of both Serratia marcescens and BCG aerosols dramatically increased at RH higher than 85%. CONCLUSIONS: Our results indicate that differences in UV dose, kinds of microorganisms, airborne particle size and RH affect UV susceptibility.

Lack of efficacy for conventional gamma irradiation of platelet concentrates to abrogate bacterial growth.

The maximum storage time for platelet concentrates is 5 days, owing to the higher risk bacterial contamination with longer storage. The expiration date could potentially be extended if a rapid system to detect microbial contamination or a safe sterilization technique could be developed and easily implemented. Gamma irradiation has decreased bacterial contamination in food products. Conventional doses of gamma irradiation were tested for their efficacy in decreasing bacterial growth during the 5-day platelet shelf life. An initial pilot study determined that bacteria suspended in normal saline at concentrations of 1 to 2 x 10(7) colony-forming units per milliliter showed a dose-related susceptibility to gamma irradiation. Subsequently, four platelet concentrates were pooled, inoculated with a known concentration of Staphylococcus autreus or Serratia marcescens, and divided. The concentrates were exposed to varying amounts of gamma irradiation, ie, no irradiation (control), 25, 50, and 75 Gy, and subjected to typical blood bank storage conditions. The platelet concentrates were sampled daily for 7 consecutive days to monitor bacterial growth by quantitative cultures. An inverse linear dose-related extinction of bacteria was evident in the pilot study with an extrapolated total kill in the 100 to 150 Gy range. There is no difference in bacterial growth with S aureus using irradiation levels from 0 to 75 Gy. A 1-day delay in bacterial growth at 75 Gy was found with S marcescens compared with units irradiated with 0 through 50 Gy. Exposure of bacteria-contaminated platelet concentrates on storage day zero to gamma irradiation at levels up to 75 Gy is ineffective at sterilizing the platelet concentrates. Higher levels of irradiation may be effective in sterilizing platelet concentrates. Function, survival, and sterility after higher than conventional levels of irradiation need further study.

Inactivation of bacteria and yeasts on agar surfaces with high power Nd:YAG laser light.

Near infrared light from a high-powered, 1064 nm, Neodymium:Yttrium Aluminium Garnet (Nd:YAG) laser killed a variety of Gram-positive and Gram-negative bacteria and two yeasts, lawned on nutrient agar plates. A beam (cross-sectional area, 1.65 cm2) of laser light was delivered in 10 J, 8 ms pulses at 10 Hz, in a series of exposure times. For each microbial species, a dose/response curve was obtained of area of inactivation vs energy density (J cm-2). The energy density that gave an inactivation area (IA) equal to 50% of the beam area was designated the IA50-value and was plotted together with its 95% confidence limits. Average IA50-values were all within a threefold range and varied from 1768 J cm-2 for Serratia marcescens to 4489 J cm-2 for vegetative cells of Bacillus stearothermophilus. There were no systematic differences in sensitivity attributable to cell shape, size, pigmentation or Gram reaction. At the lowest energy densities where inactivation was achieved for the majority of organisms (around 2000 J cm-2), no effect was observed on the nutrient agar surface, but as the energy density was increased, a depression in the agar surface was formed, followed by localized melting of the agar.

The effectiveness of a u-v toothbrush sanitizing device in reducing the number of bacteria, yeasts and viruses on toothbrushes.

Sixty-six sterile toothbrushes were exposed to one of the following microorganisms: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillis subtilis, Serratia marcescens and Baker's yeast. The Pollenex DS60 Daily Dental Sanitizer was found to be effective in substantially reducing the number of retained bacteria and yeasts as compared to contaminated toothbrushes not treated with such a device. Different toothbrush types had different response rates. Seventy-two sterile toothbrushes were exposed to Herpes Simplex Virus, Type I and seventy-two sterile toothbrushes were exposed to Parainfluenza Virus, Type III. The Pollenex DS60 Daily Dental Sanitizer consistently killed both viruses on all of the toothbrushes treated. Both viruses were consistently retained on non-treated toothbrushes for at least 24 hours.

Ultraviolet disinfection of contact lenses.

To evaluate the efficacy of ultraviolet (UV) radiation as a method of disinfecting contact lenses and their storage solutions, we contaminated soft lenses (Bausch & Lomb Optima 38), rigid gas permeable (RGP) lenses (Oxyflow F-30), and their storage solutions with three common bacteria. Escherichia coli (E.c.), Staphylococcus epidermis (S.e.), and Serratia marcescens (S.m.). The storage solutions used were saline solution and RGP conditioning solution. We determined the exposure times to 253.7-nm wavelength UV radiation necessary to disinfect the contact lenses and solutions. The decimal reduction values (D values) found for UV radiation were 10 to 200 hundred times shorter than reported for currently available disinfection systems. For E.c., sterilization was attained after 100 s of exposure. For S.e. and S.m., sterilization occurred after 300 s of exposure. Different contact lens solutions transmit UV radiation to various degrees, with saline solution passing more than 90% of the UV radiation. Thus, our results indicate that UV radiation is an effective and rapid method of disinfecting contact lenses and their storage solutions.

Bactericidal effectiveness of modulated UV light.

Studies were designed to evaluate the effectiveness of pulsed modulated UV light waveforms for killing bacteria. Exposure of five strains of bacteria to the modulated information encoded in the light decreased the colony population from a confluent lawn to less than 20 colonies. However, approximately 2,000 colonies survived treatment with the same intensity and time of exposure to UV light lacking the modulated information.