engleski

Molecular characterization of Acinetobacter baumannii from Zagreb wastewater treatment plant

Objectives: Urban wastewater from the City of Zagreb, containing a fraction of raw hospital wastewaters, is treated at the secondary wastewater treatment plant (WWTP). Acinetobacter baumannii recovered during one-year monitoring (2015-16) at the main stages of the WWTP were characterized to elucidate the efficiency of WWTP in removal of this emerging hospital pathogen. Methods: Recovery of A. baumannii was performed on CHROMagar Acinetobacter plates. Isolates were identified by MALDI-TOF MS. Antimicrobial susceptibility testing was performed and interpreted according to EUCAST breakpoints for clinical A. baumannii isolates. Molecular characterization was performed by WGS and cgMLST. Results: A. baumannii isolates were continuously recovered from different stages of the WWTP: influent wastewater, activated sludge, digested sludge, effluent wastewater, except from lime-treated waste sludge. Isolates resistant to carbapenems and fluoroquinolones (CFQR) dominated (82%) in all stages of WWTP, but coexisted with 14% of susceptible isolates. Pan-drug resistant (PDR) isolates (3%) were detected in activated sludge and effluent wastewater. The majority of CFQR and PDR isolates belonged to IC2 (ST-195Oxford/ST-2Pasteur), and a minority to IC1, while susceptible isolates were unclustered. Carbapenem resistance was mediated by acquired blaOXA-23 in IC2 isolates and blaOXA-72 in IC1 isolates. The CFQR and PDR A. baumannii belonging to ST-195 were previously reported in the same period of monitoring (2015-16) from hospitalised patients, hospital wastewater, and the Sava River. Close relatedness with isolates recovered from Zagreb WWTP suggests dissemination of A. baumannii of clinical significance from patients, via untreated hospital wastewater, urban sewage, and WWTP to the Sava River. Conclusion: Clinically relevant A. baumannii persist in secondary WWTP and are emitted via effluent to the Sava River. Alkaline lime-treatment renders the waste sludge free of viable A. baumannii. However, additional disinfection of effluent prior to its discharge into the natural recipient is needed to avoid the possible public-health risk.

Acinetobacter baumannii, wastewater, resistance

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