Tracking Down Antibiotic-Resistant <em>Pseudomonas aeruginosa</em> Isolates in a Wastewater Network

<div><p>The <em>Pseudomonas aeruginosa</em>-containing wastewater released by hospitals is treated by wastewater treatment plants (WWTPs), generating sludge, which is used as a fertilizer, and effluent, which is discharged into rivers. We evaluated the risk of dissemination of antibiotic-resistant <em>P. aeruginosa</em> (AR-<em>PA</em>) from the hospital to the environment via the wastewater network. Over a 10-week period, we sampled weekly 11 points (hospital and urban wastewater, untreated and treated water, sludge) of the wastewater network and the river upstream and downstream of the WWTP of a city in eastern France. We quantified the <em>P. aeruginosa</em> load by colony counting. We determined the susceptibility to 16 antibiotics of 225 isolates, which we sorted into three categories (wild-type, antibiotic-resistant and multidrug-resistant). Extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) were identified by gene sequencing. All non-wild-type isolates (<em>n</em> = 56) and a similar number of wild-type isolates (<em>n</em> = 54) were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Almost all the samples (105/110, 95.5%) contained <em>P. aeruginosa</em>, with high loads in hospital wastewater and sludge (≥3×10⁶ CFU/l or/kg). Most of the multidrug-resistant isolates belonged to ST235, CC111 and ST395. They were found in hospital wastewater and some produced ESBLs such as PER-1 and MBLs such as IMP-29. The WWTP greatly reduced <em>P. aeruginosa</em> counts in effluent, but the <em>P. aeruginosa</em> load in the river was nonetheless higher downstream than upstream from the WWTP. We conclude that the antibiotic-resistant <em>P. aeruginosa</em> released by hospitals is found in the water downstream from the WWTP and in sludge, constituting a potential risk of environmental contamination.</p>