AimsTo investigate Pseudomonas aeruginosa isolates from a hospital wastewater treatment plant (HWTP), focusing on enzyme-based mechanisms of -lactams resistance and the genetic relatedness among isolates. Methods and ResultsForty-one Ps.aeruginosa strains recovered from a HWTP were identified by amplification of 16S rRNA gene. -lactamase production was screened by disc diffusion, CHROMagar extended-spectrum -lactamase (ESBL) and -lactamase strips. -lactamase and ESBL producing isolates were investigated by PCR for the presence of ESBL, metallo--lactamase and Klebsiella pneumoniae carbapenemase encoding genes. Thirty-four isolates (83%) were resistant to at least one antibiotic belonging to three or more classes. Out of these 34 isolates, 28 (82%) were classified as multidrug-resistant (MDR) and 6 (18%) extensively drug-resistant (XDR). Genetic relatedness by Enterobacterial Repetitive Intergenic Consensus sequence-PCR and Multilocus sequence typing analysis showed 20 distinct profiles and 15 sequencing types respectively. Clonal Complex 244 (CC244) shows the pathogenic potential of this clone carrying MDR and XDR strains from clinical, environmental and hospital waste sources. ConclusionsOur results suggest that treatment facilities for hospital wastewater can stimulate the increase of antimicrobial resistance bacteria and genes. Significance and Impact of the StudyThe great genetic diversity of Ps.aeruginosa recovered from HWTP constantly released into aquatic systems allow the spread of antimicrobial-resistant organisms and genes.