Inactivation of E. coli and E. faecalis by solar photo-Fenton with EDDS complex at neutral pH in municipal wastewater effluents.

Photo-Fenton is a solar disinfection technology widely demonstrated to be effective to inactivate microorganisms in water by the combined effect of photoactivated iron species and the direct action of solar photons. Nevertheless, the precipitation of iron as ferric hydroxide at basic pH is the main disadvantage of this process. Thus, challenge in photo-Fenton is looking for alternatives to iron salts. Polycarboxylic acids, such as Ethylendiamine-N',N'-disuccinic acid (EDDS), can form strong complex with Fe3+ and enhance the dissolution of iron in natural water through photochemical process. The aim of this study was to evaluate the disinfection effectiveness of solar photo-Fenton with and without EDDS in water. Several reagent concentrations were assessed, best bacterial (Escherichia coli and Enterococcus faecalis) inactivation was obtained with 0.1:0.2:0.3 mM (Fe3+:EDDS:H2O2) in isotonic water. The benefit of using EDDS complexes to increase the efficiency of kept dissolved iron in water at basic pH was proven. Solar disinfection and H2O2/solar with and without EDDS, and Fe3+:EDDS complexes were also investigated. Bacterial inactivation results in municipal wastewater effluents (MWWE) demonstrated that the competitive role of organic matter and inorganic compounds strongly affect the efficacy of Fe3+:EDDS at all concentrations tested, obtaining the fastest inactivation kinetics with H2O2/solar (0.3 mM).

Enhanced visible light photocatalytic disinfection of gram negative, pathogenic Escherichia coli bacteria with Ag/TiV oxide nanoparticles.

Silver sensitized titanium vanadium mixed Ag/TiV oxide photocatalyst was synthesized using sol-gel technique. The catalyst was characterized using XRD, SEM, EDAX, HRTEM, UV-DRS, XPS, and PL analysis which reveal the formation of a predominantly rutile mixed phase nanoparticles of 25-30 nm crystallite size. The catalyst showed a marked red-shift in the absorption spectrum compared to Degussa P25. It exhibited a remarkable enhancement in the visible light photocatalytic activity in inactivating Escherichia coli, a gram-negative pathogenic bacterium, too. The conclusions are supported by a comparison with an identically synthesized TiV oxide sample. A microbicidal photonic efficiency (MPE) has been defined and a method for its determination has been proposed to facilitate quantification of the performance of the photocatalyst and the disinfection system taking into account the response of the catalyst to the radiation intensity.

Effects of 810 nm laser irradiation on in vitro growth of bacteria: comparison of continuous wave and frequency modulated light.

BACKGROUND AND OBJECTIVES: Low intensity laser therapy may modify growth of wound bacteria, which could affect wound healing. This study compares the effects on bacteria of 810 nm laser using various delivery modes (continuous wave or frequency modulated light at 26, 292, 1000, or 3800 Hz). STUDY DESIGN/MATERIALS AND METHODS: Staphylococcus (S.) aureus, Escherichia (E.) coli, and Pseudomonas (P.) aeruginosa were plated on agar and then irradiated (0.015 W/cm(2); 1-50 J/cm(2)) or used as controls (sham irradiated); growth was examined after 20 hours of incubation post exposure. RESULTS: There were interactions of species and modulation frequency in the overall effects of irradiation (P = 0.0001), and in the radiant exposure mediated effects (P = 0.0001); thus individual frequencies and each bacterium were analysed separately. Bacteria increased following 3800 Hz (P = 0.0001) and 1000 Hz (P = 0.0001) pulsed irradiation; at particular radiant exposures P. aeruginosa proliferated significantly more than other bacteria. Pulsed laser at 292 and 26 Hz also produced species-dependent effects (P = 0.0001; P = 0.0005); however, the effects for different radiant exposures were not significant. Bacterial growth increased overall, independent of species, using continuous mode laser, significantly so at 1 J/cm(2) (P = 0.02). Analysis of individual species demonstrated that laser-mediated growth of S. aureus and E. coli was dependent on pulse frequency; for S. aureus, however, there was no effect for different radiant exposures. Further tests to examine the radiant exposure effects on E. coli showed that growth increased at a frequency of 1000 Hz (2 J/cm(2); P = 0.03). P. aeruginosa growth increased up to 192% using pulsed irradiation at 1000-3800 Hz; whereas 26-292 Hz laser produced only a growth trend. CONCLUSIONS: The findings of this study point to the need for wound cultures prior to laser irradiation of infected wounds. Similar investigations using other common therapeutic wavelengths are recommended.

Specific labeling and physical characterization of R-factor deoxyribonucleic acid in Escherichia coli.

The molecular nature of R-factor deoxyribonucleic acid (DNA) was examined in Escherichia coli by using a method for the specific labeling of the derepressed R factor, R1, in a female cell after conjugation. Sixty minutes after mating, the R factor was isolated as a single molecule with a molecular weight of 65 x 10(6) daltons. This single molecular species sedimented as either a covalently closed molecule or a "nicked" circle. When the single R-factor component was centrifuged in a CsCl density gradient, only a single homogeneous species with a buoyant density of 1.711 g/cm(3) was observed. R-factor DNA was also isolated directly from exponentially growing cells of E. coli as a covalently closed single molecular species comprising about 1% of the total cellular DNA. Previous studies in Proteus show that R1 factor DNA components of buoyant density 1.709, 1.711, and 1.716 g/cm(3) can be identified as distinct replicons. It is suggested that the single molecule of R1 observed in E. coli is most simply explained as a composite structure resulting from a recombinational assemblage of a 1.709 and 1.716 g/cm(3) replicon.