Environmental Dispersion of Multiresistant in Aquatic Ecosystems in an Area of Spain with a High Density of Pig Farming.

: This study aimed to (a) assess the prevalence of multidrug-resistant (MDR) in the waters of two rivers and wastewater treatment plants (WWTPs) in a region of Catalonia, Spain; (b) genetically characterize the MDR strains; and (c) compare extended-spectrum β-lactamase (ESBL)-producing isolates from environmental and human sources. : A total of 62 samples were collected from the influent and effluent of 31 WWTPs and 29 river water samples from 11 sites. Simultaneously, 382 hospitalized patients were screened for MDR using rectal swabs. All isolates underwent antibiotic susceptibility testing and whole-genome sequencing. : MDR were detected in 48.4% of WWTP samples, with 18.5% ESBL-producing and 1.5% (one sample) OXA-48-producing in influents, and 12.8% ESBL-producing in effluents. In river waters, 5.6% of samples contained ESBL-producing and 1.4% (1 sample) contained VIM-producing complex strains. Among patients, 10.2% (39/382) carried MDR Gram-negative bacilli, of which 66.7% were ESBL-producing . In aquatic ecosystems ST131 (13.3%) and ST162 (13.3%) were the most common strains, while in humans the common were ST131 (33.3%), ST69 (11.1%) and ST410 (7.4%) in humans. The most frequent environmental antibiotic resistance genes (ARG) were (24%) and (20%), while the most common ARGs were (20.4%), (18.4%) and (14.3%). IncF plasmids were predominant in environmental and human strains. : ESBL-producing and carbapenemase-producing are present in aquatic environments in the region. Phylogenetic similarities between environmental and clinical strains suggest a possible similar origin. Further studies are necessary to clarify transmission routes and environmental impact.