Abstract

In this study the removal of resistant Enterococcus spp. was evaluated using the laboratory-scale wastewater treatment model plant (M-WWTP), designed as a multiphase (anaerobic, anoxic and aerobic) system (Q = 27 dm3 per day) and continuously supplied with the wastewater obtained from the full-scale WWTP, after grid. The activated sludge from the secondary clarifier was recirculated to the anaerobic chamber (with the ratio equal to 100% of the flow rate) and additionally, due to the specific work conditions, the effluent from the aerobic reactor was also recirculated into the anoxic reactor to support the denitrification processes (up to 600% of the flow rate). The number of Enterococcus spp. in M-WWTP influent and effluent, as well as in aerobic chamber was determined using selective medium. Diversity and resistance patterns among selected isolates of Enterococcus spp. (n=152) was analyzed by Phoenix Automated Microbiology System (BD Biosciences, USA). Susceptibility of the isolates was tested against high level gentamicin (GMS), high level streptomycin (STS), ampicillin (AM), vancomycin (VA), erythromycin (E), ciprofloxacin (CIP) and tetracycline (TE). The enterococci isolates were identified as E. faecium (56.6%) and E. faecalis (42.7%), as well as one isolate belonged to E. hirae (0.7%). In the isolate of E. hirae resistance patterns to AM and TE were detected. In case of E. faecium and E. faecalis the most frequent the resistance to E (up to 75%) was detected and followed by resistance to CIP (up to 57%) and TE (up to 46%). Substantial concern should be paid to the presence of enterococci with multiple antimicrobial resistance patterns (MAR) as well as with resistance to high level aminoglycosides (GMS and STS) and glycopeptides (VA), antimicrobials of clinical significance. Since during the treatment processes the positive selection of the isolates with antimicrobial resistance was observed, the potential dissemination of antibiotic resistance genes by wastewater treated in activated sludge processes should be taken under consideration.

Authors (5)