This study evaluated the ability of a sewage treatment plant to eliminate Listeria species and the incidence of Listeria species in the river receiving the effluent. The average efficiency of removal of Listeria species in the treatment plant was 92%. Despite the efficiency of the plant being within the limits established by the EC Directive in terms of BOD5 decrease, an increase in the levels of Listeria species was still observed downstream from the plant. The species isolated with greatest frequency, both in the influent and effluent as well as the river water, was L. monocytogenes followed by L. seeligeri and L. welshimeri. L. ivanovii was only found in very low proportions in the river samples. The analysis of the sensitivity of Listeria species to 22 antimicrobial agents demonstrated the presence of a high percentage of bacteria resistant to aztrenam, cefuroxme, cetriaxone and to a leser degree moxalactam and cefotaxime. In contrast, resistance to aminoglycosides and tetracycline was only observed in a low number of isolates.
The aim of this study was to assess the number of both extended-spectrum -lactamases (ESBL) producing Enterobacteriaceae and vancomycin-resistant enterococci (VRE) present in the inflow (hospital and urban sewage) and effluent waste water treatment plant (WWPT) and receiving waters.The results show that the average counts of ESBL producing Enterobacteriaceae in hospital sewage were much higher (more than 2.5 logs) than those observed in urban waste water. On the other hand, the sewage treatment plant studied did not perform well in removing pathogenic microorganisms. Although Enterobacteriaceae concentrations were reduced in the final effluent by almost two log units as compared with the crude sewage concentrations, a high number of Enterobacteriaceae were detected in the effluent, representing a risk for microbiological pollution of water resources. A strong increase in ESBL-producing bacteria in the receiving water was detected after effluent discharge WWPT.The results obtained have also demonstrated that the hospital sewage releases a high concentration of VRE (> 3.0 x 10 5 CFU/100 ml), which represents 25% of the total population of enterococci presents in these waters. The hospital sewage contains a proportion of VRE 10 times higher in comparison with that detected in the urban sewage. The VRE proportion in the urban sewage was very low (2.6%) and constant along the different samplings. In the other hand, sewage discharged from municipal sewage treatment plant effluent also increased the VRE proportion in the river Sar water (1.5% of EVR in upstream to 3.8% downstream from the plant). resistant bacteria and resistance genes to the environment and possibly to the human and animal population.
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