Genomic characterization of colistin- and carbapenem-resistant Pseudomonas aeruginosa ST1560 from Guanabara Bay, Brazil

AIMS: This study aimed to characterize a colistin- and carbapenem-resistant Pseudomonas aeruginosa ST1560 strain isolated from Guanabara Bay, Brazil, and to investigate the molecular mechanisms underlying its resistance phenotype. METHODS AND RESULTS: Six surface water samples from Guanabara Bay were collected, yielding 71 P. aeruginosa subjected to antimicrobial susceptibility testing. Three isolates exhibited elevated minimal inhibitory concentrations (MICs) to colistin (≥512, 64, and 8 mg/l) in the absence of mcr genes (1-10). Among these, only strain CCVSU 5861 demonstrated carbapenemase confirmed by Blue Carba test. This strain was selected for whole-genome sequencing (Illumina). Genomic analysis identified the presence of blaKPC-2 and blaOXA-395, along with additional resistance determinants associated with aminoglycosides and fosfomycin. Genes involved in lipopolysaccharide modification, (arnA, arnT, and basS) were also detected, likely contributing to colistin resistance. The blaKPC-2 gene was located adjacent to the mobile genetic element ISKpn6, suggesting potential horizontal gene transfer. CONCLUSIONS: The P. aeruginosa ST1560 displays a complex multidrug resistance profile, including resistance to both colistin and carbapenems. This phenotype appears to be mediated by a combination of acquired resistance genes and chromosomal mechanisms. The localization of blaKPC-2 within a mobile genetic element underscores the risk of dissemination in aquatic environments.