Resistant K. pneumoniae in Barcelona WWTPs
The World Health Organization classifies extended-spectrum beta-lactamase (ESBL) and carbapenemase-producing Klebsiella pneumoniae as critical priority pathogens due to their high incidence, mortality, transmissibility, rapid resistance acquisition, and limited treatment options. Beyond clinical settings, their detection in wastewater treatment plants (WWTPs) is particularly alarming, as these facilities can promote their persistence and environmental dissemination.  This study characterized 37 antibiotic-resistant K. pneumoniae strains isolated from two WWTPs in the metropolitan area of Barcelona, analyzing their antimicrobial resistance (AMR) profiles, antimicrobial resistance genes (ARGs), biocide and heavy metal tolerance genes (HMTGs), virulence factor genes (VFGs), biofilm-forming capacity and conjugation ability. Among them, 70.3% were multidrug-resistant (MDR) and 16.2% extensively drug-resistant. Whole-genome sequencing revealed diverse ARGs; all strains carried beta-lactam resistance genes, including 14 ESBL and 12 carbapenemase producers. Nearly all strains (96.9%) carried biocide or HMTGs, and 64.9% harbored integrons. Furthermore, all strains carried VFGs. Identical sequence types (STs) detected across sampling periods, treatment stages, and between WWTPs indicate long-term persistence, resistance to water treatments, and inter-facility dissemination.  Most strains (67.6%) displayed weak to moderate biofilm-forming, and conjugation assays confirmed the horizontal gene transfer in five of seven ESBL-producing strains tested. High-risk clones, including ST15, ST147, and ST307, were particularly enriched in the IFAS secondary treatment stage of the Gavà-Viladecans WWTP. The three strains recovered from the reclaimed water of the Baix Llobregat WWTP were ESBL or carbapenemase producers, indicating a continued risk of environmental dissemination.  Strengthening wastewater management and regulatory frameworks is essential to limit the spread of these pathogens and safeguard public health.