Presence of bacterium Acinetobacter baumannii in wastewaters of the City of Zagreb

Acinetobacter baumannii is an emerging hospital pathogen causing outbreaks in Croatia since 2002 and is still present in Croatian hospitals. Clinical isolates of A. baumannii in Croatian hospitals are usually multi-drug resistant(MDR), with resistance to carbapenems dramatically increasing from 10% in 2008 to 82% in 2014. Although A. baumannii has been isolated from patients and hospital environment during outbreaks, crucial questions regarding its epidemiology remains incompletely understood. The aim of this study was to screen the hospital and municipal wastewater of the City of Zagreb for the presence of viable A. baumannii and carbapenems. Sampling of hospital wastewater was performed on 2 occasions in 2015 at the central manhole of one Zagreb’s hospital from which the clinical isolates of A. baumannii were recovered. Sampling of municipal wastewater was performed on 6 occasions in 2014/15 at the influent and effluent of the central Zagreb’s wastewater treatment plant. Concentration of carbapenems in wastewater was measured by UHPLC Q-TOF MS. The isolation of A. baumannii from wastewater was performed at 42C/48h on CHROMagar Acinetobacter without or with the addition of commercial supplement CR102 which allows the growth of carbapenem-resistant isolates. Presumptive A. baumannii colonies were characterized phenotypically, by using Vitek2 system, and MALDI-TOF MS. Antibiotic resistance profiles were determined by Vitek2 system and interpreted according to EUCAST criteria. Hospital and municipal wastewaters contained high concentrations of imipenem and meropenem which averaged: 894 and 129ng/L in hospital wastewater, 3060 and 380ng/L in raw and 497 and 311ng/L in treated municipal wastewater, respectively. From hospital wastewater, raw and treated municipal wastewater 8, 30 and 7 isolates of A. baumannii were recovered, respectively. All isolates from hospital wastewater and majority (33/37) of isolates from municipal wastewater were resistant to carbapenems and majority of tested antibiotics except colistin. The 7 MDR clinical isolates recovered in the same period showed comparable levels of antibiotic resistance to MDR isolates from hospital and municipal wastewater. These suggest that A. baumannii is able to survive in environment outside hospitals. However, 4 isolates from raw municipal wastewater were susceptible to carbapenems and other antibiotics. This finding opens the possibility that A. baumannii could have natural habitat in sewage system.