Abstract
The Pseudomonas aeruginosa-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 P. aeruginosa (AR-PA) 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 P. aeruginosa 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 (n = 56) and a similar number of wild-type isolates (n = 54) were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Almost all the samples (105/110, 95.5%) contained P. aeruginosa, 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 P. aeruginosa counts in effluent, but the P. aeruginosa load in the river was nonetheless higher downstream than upstream from the WWTP. We conclude that the antibiotic-resistant P. aeruginosa released by hospitals is found in the water downstream from the WWTP and in sludge, constituting a potential risk of environmental contamination.
Highlights
Pseudomonas aeruginosa is a rod-shaped Gram-negative aerobic bacterium that can grow in many niches, but prefers moist environments
Analysis of multi-locus sequence typing (MLST) data We investigated the evolutionary relationship between isolates with the minimal spanning tree (MST) algorithm, which is based on allelic profiles
The effluent treatment carried out by the wastewater treatment plants (WWTPs) resulted in an overall P. aeruginosa clearance rate of 94.0% (2.56105 CFU/l in untreated water versus 1.16104 CFU/ml in treated water; p = 0.0001)
Summary
Pseudomonas aeruginosa is a rod-shaped Gram-negative aerobic bacterium that can grow in many niches, but prefers moist environments. It is found in both low-nutrient or oligotrophic environments and highly nutritious environments, such as sewage and the human body. Hospital outbreaks linked to multidrug-resistant strains of P. aeruginosa are widely reported [2,3,4,5]. Multidrugresistant P. aeruginosa is thought to emerge principally at hospitals, where large amounts of antibiotics are used [9]. Antibiotic resistance in P. aeruginosa mostly results from chromosomal mutations, but may be acquired by horizontal gene transfer [10]. High-level resistance to these compounds is achieved by AmpC cephalosporinase overproduction or by the production of acquired b-lactamases with an extended spectrum (i.e. ESBLs, MBLs and extended-spectrum oxacillinases) [11]
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