Genomic analysis reveals multi-lineage carbapenem-resistant Pseudomonas aeruginosa mimicking a hospital outbreak

BACKGROUND: Pseudomonas aeruginosa is a major cause of nosocomial infections, often exhibiting multidrug resistance (MDR) and high genetic adaptability. This study investigated temporal cluster of MDR P. aeruginosa isolates obtained from five different hospitalized patients within a single healthcare facility. The isolates shared similar antimicrobial resistance patterns, suggesting a common source or transmission event. However, pulsed-field gel electrophoresis (PFGE) genotyping identified four distinct clones, indicating clonal heterogeneity rather than a single-strain outbreak. To further elucidate the genetic basis of resistance, virulence, and genomic diversity, whole-genome sequencing (WGS) was performed. RESULTS: type β-lactamases, and a wide variety of efflux pumps (such as MexAB-OprM, MexCD-OprJ MexGHI-OpmD, MexJK-OprM, MexMN-OprM, MexPQ-OpmE, MuxABC-OpmB). Virulome analysis identified key pathogenicity determinants related to biofilm formation, adherence, motility, immune evasion, toxin and other virulence traits. Multiple mobile genetic elements were determined, suggesting horizontal gene transfer (HGT) as a significant factor in the dissemination of resistance traits. CONCLUSION: These findings demonstrate that nosocomial outbreak-like event of MDR P. aeruginosa can involve multiple unrelated clones co-circulating within the same hospital environment, challenging traditional epidemiological assumptions. Despite a high degree of core genome synteny and similar resistance profiles, the identification of four distinct clones among simultaneous patient cases indicates that the outbreak was not caused by a single strain. These results further emphasize the potential for multiple co-circulating clones in MDR P. aeruginosa outbreaks and challenge assumptions of single-source transmission. Whole-genome sequencing plays a critical role in understanding transmission dynamics and guiding infection control strategies.