Emission of extensively-drug-resistant Acinetobacter baumannii from hospital settings to the natural environment.

BACKGROUND: Acinetobacter baumannii is a leading emerging pathogen that is frequently recovered from patients during hospital outbreaks. The role of environmental A. baumannii reservoirs is therefore of great concern worldwide.

AIM: To investigate the connection between A. baumannii causing hospital outbreaks and environmental isolates from hospital wastewater, urban sewage and river water as the final natural recipient of wastewaters.

METHODS: Clinical isolates from patients with hospital-acquired pneumonia and environmental isolates from water were collected during a two-month monitoring period. Recovery of A. baumannii was performed using CHROMagar Acinetobacter plates, incubated at 42°C for 48 h. Identification was performed by matrix-assisted laser desorption ionization-time of flight mass spectrometry and analyses of rpoB gene. The antibiotic resistance profiles were interpreted according to criteria given for clinical isolates of A. baumannii. The sequence types (ST) were retrieved by multi-locus sequence typing.

RESULTS: Fourteen of 19 isolates recovered from patients, hospital wastewaters, urban sewage and river water belonged to ST-195. The remaining five isolates recovered from patients and river water were assigned to ST-1421. All isolates showed very strong relatedness and clustered into CC92, which corresponds to IC2. All isolates were non-susceptible to at least one agent in all but two or fewer antimicrobial categories, and thus were classified as 'extensively-drug-resistant' (XDR). Heteroresistance to colistin was found in two isolates from hospital wastewater.

CONCLUSION: Close relatedness of clinical and environmental isolates suggests the emission of XDR A. baumannii via the untreated hospital wastewater in the natural environment.