The fate of carbapenem-resistant bacteria in a wastewater treatment plant.

Wastewater treatment plants have been considered potential sources of antibiotic resistance gene exchange and release into the environment. The aim of our study was to quantify environmental and human-associated carbapenem-resistant bacterial populations (CRBPs) across wastewater treatment stages and correlate bacterial counts to physicochemical and other bacteriological parameters in order to see their behaviour in wastewater and sludge and their potential dissemination in the environment. Samples were taken from five sites (treatment stages) of the largest Croatian wastewater treatment plant (20 per site) over 10 months of monitoring. CRBPs were found at all wastewater treatment stages save for the lime-treated, stabilised sludge, which underlines the importance of effluent and digested sludge disinfection. Secondary sludge settling removed 99% of CRBP from the effluent, but the relative proportion of CRBP in the total bacterial count significantly increased in the effluent (0.0020%) and digested sludge (0.0019%) compared to the influent (0.0006%), indicating selection for resistant bacteria in these settings. CRBP counts did not correlate with measured carbapenem concentrations in wastewater, which suggests that antibiotic concentrations were not the reason for CRBP selection. Negative correlation between activated sludge retention time and CRBP indicated that their number could be reduced by increasing the retention time during secondary treatment. Despite the indications that WWTPs select for antibiotic-resistant bacteria, wastewater treatment is very efficient in reducing their absolute numbers, and proper effluent and sludge disinfection can significantly reduce dissemination of antibiotic-resistant bacteria into the environment.

A novel amperometric method for antioxidant activity determination using DPPH free radical.

A new method for the determination of antioxidant activity based on the amperometric reduction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at the glassy carbon electrode is proposed. All experiments were done in three-electrode electrochemical cell at 140 mV vs. Hg(2)Cl(2) | 3 M KCl using ethanolic solution (phi=40%) and 0.033 M KCl in 0.033 M phosphate buffer, pH=7.4. The linear range obtained for Trolox in 100 microM DPPH ethanol-water solution was up to 30 microM, with a limit of detection of 0.05 microM. The developed method was applied for the evaluation of antioxidant activity of some water or ethanol soluble pure compounds of antioxidants and of the samples of tea, wine and some other beverages. The good correlation of measurements (R(2)=0.9993) expressed as Trolox equivalent was obtained between the proposed amperometric method and classic spectroscopic method.