The effects of ultraviolet disinfection on vancomycin-resistant Enterococcus faecalis.

The emergence of vancomycin-resistant Enterococcus faecalis (E. faecalis) in water is threatening the health of human beings. The effect of ultraviolet disinfection on vancomycin-resistant E. faecalis, including the effectiveness, photoreactivation and dark repair of E. faecalis, and the deactivation mechanism were investigated in this work. Ultraviolet disinfection could quickly inactivate the target antibiotic resistant bacterium (ARB), E. faecalis, and it caused damage to the cell membrane and induced the decrease of the total adenosine triphosphate (ATP) content and the superoxide dismutase (SOD) activity significantly (p < 0.05). E. faecalis could reactivate after ultraviolet disinfection especially under light conditions. Furthermore, the removal of the selected antibiotic resistance gene (ARG), vanB, by ultraviolet radiation and the effect on the vancomycin resistance of E. faecalis were investigated, which showed that ultraviolet disinfection had no significant effect on the vancomycin resistance of E. faecalis (p > 0.05).

Effect of bicarbonate on physiochemical properties of silver nanoparticles and toxicity to Escherichia coli.

Understanding the interaction between silver nanoparticles (Ag NPs) and substances in aquatic systems enables Ag NPs to be better applied in science and industry. Moreover, it also could help us to determine the fate of Ag NPs and assess their hazards in aquatic environment. In this work, the interaction of Ag NPs with HCO3-, ubiquitous ligand in aquatic systems, during long-term incubation was firstly studied and the possible mechanism was proposed. Results showed that the long-term incubation with HCO3- led to the red-shifting of UV-vis spectra, the increasing of particles zeta potential (more negative), and the declining of the aqueous Ag+ concentration, as well as the decreasing in the toxicity of Ag NPs suspensions. Furthermore, the ambient temperature was found to have a great impact on the interaction of Ag NPs with HCO3-. The reaction process between Ag NPs and HCO3- was revealed by H2O2 mediated oxidation experiments. An ultrathin Ag2CO3 layer was proved to form on the surface of Ag NPs, which should be the reason for the evolution of various properties of Ag NPs described above.

Inactivation of two Mycobacteria by free chlorine: Effectiveness, influencing factors, and mechanisms.

Chlorination is one of the most widely used disinfection techniques, and the problem of "chlorine-resistant bacteria" (CRB) has attracted more attention recently. In this study, the deactivation of typical CRB in water, Mycobacterium fortuitum (M. fortuitum) and Mycobacterium mucogenicum (M. mucogenicum), by free chlorine was investigated with Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) as the reference. The chlorination effectiveness of chlorine on M. fortuitum and M. mucogenicum and the effect of chlorine concentration, pH, and humic acid were studied. It was found that M. mucogenicum was more resistant to chlorine than M. fortuitum, both of which were much more resistant than E. coli and B. subtilis. The effect of disinfectant concentration on the inactivation efficiency was positive, whereas the influence of pH and humic acid was negative. The inactivation mechanisms were explored by analyzing the bacteria morphology, the destruction of cell membrane, the cell hydrophobicity, as well as total adenosine triphosphate (ATP), superoxide dismutase (SOD) activity. The slight destruction of the cell membrane was observed after deactivation with chlorine, and high hydrophobicity of the cell membrane combined with metabolic changes might lead to the chlorine tolerance of Mycobacteria.

The combined effect of light irradiation and chloride on the physicochemical properties of silver nanoparticles.

Understanding the effect of various environmental factors on the transformation of silver nanoparticles (Ag NPs) is crucial to determine their toxicity and fate in the environment. Ag NPs are inevitably exposed to sunlight and will be in contact with chloride (Cl-), a ubiquitous ligand in natural water, once released into the environment. In this study, the combined effect of Cl- and light on various physicochemical properties (optical property, dissolution, morphology, surface charge) of different sizes Ag NPs was studied. The results showed that light irradiation, in the presence of Cl-, led to a great decrease in the concentration of dissolved Ag and a remarkable increase in the zeta potential of Ag NPs, as well as the generation of some tiny Ag NPs and fusion aggregates. AgCl was suggested to rapidly coat onto Ag NPs after exposure to Cl-. And the AgCl layer was obviously destroyed by photoreduction under light irradiation. Meanwhile, the Ag NP size exhibited a great impact on the destruction of the AgCl layer. It was further observed that the AgCl layer gradually re-formed when the light was removed, which suggested that Ag NPs might present different states during the daytime and at night in aquatic environments.

Antibacterial performance of polymer quaternary ammonium salt-capped silver nanoparticles on Bacillus subtilis in water.

In this study, we prepared polymer quaternary ammonium salt-capped silver nanoparticles (PQAS-AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS-AgNPs on Bacillus subtilis (B. subtilis), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS-AgNPs revealed excellent antimicrobial activity to B. subtilis, compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS-AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS-AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS-AgNPs decreased in the presence of Cl- and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS-AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.

The decay of silver nanoparticles in preoxidation process.

To investigate the fate of metal-based nanoparticles in water oxidation treatment processes, the decay of Ag-NPs in the presence of three kinds of water treatment preoxidants, sodium hypochlorite (NaClO), hydrogen peroxide (H2O2) and potassium permanganate (KMnO4), was investigated in this work. Dissolution of Ag-NPs into silver ions (Ag+) was found to occur under exposure to NaClO, H2O2 and KMnO4. The morphology of Ag-NPs changed after reacting with NaClO, H2O2 and KMnO4. Factors affecting the decay of Ag-NPs, i.e., the dosage of oxidants, pH, the presence of humic acid, typical ions in water, and the size of the nanoparticles, were investigated. A higher dosage of oxidants, the presence of calcium ions, and lower size of Ag-NPs promoted the decay of Ag-NPs. The presence of humic acid and sulfide ions inhibited the decay of Ag-NPs. The decay of Ag-NPs under exposure to oxidants was significantly affected by the pH. The mechanism of the Ag-NPs in the presence of oxidants under different environmental conditions is also discussed.

[Effects of Anions on Bromate Formation During Ozonation of Bromide-Containing Water].

To study the effects of common inorganic anions on bromate formation during ozonation of bromide-containing water, the effects of different mass concentrations of Cl-, HCO3-, and SO(4)2- on bromate formation were investigated in bench-scale test. The mechanisms of these three coexisting anions on bromate formation was analyzed based on the ozone decomposition, HOBr/OBr- formation, and transformation of total bromine species. Our results showed that adding of 3-150 mg.L-1 Cl- can reduce 8. 8%-25. 7% of bromate formation within 60 min. 63. 9% of bromate would be decreased by increasing SO(4)2- concentration from 0 mg.L-1 to 30 mg.L-1 within 20 min. However, more than 6. 4 times the mass concentrations of bromate were formed as HCO3- mass concentrations increased from 0 mg.L-1 to 30 mg.L-1 within 20 min. The production of bromate was slightly increased when HCO3- mass concentrations was above 30 mg.L-1. Under the condition of the same ozone dosage and reaction time, adding of Cl- and SO(4)2- will inhibit the formation of bromate during ozonation, while adding of HCOC3- significantly will increase the production of bromate.