Molecular characteristics and antimicrobial susceptibility profiling of carbapenem-resistant Pseudomonas aeruginosa clinical isolates in Korea: Implications for novel β-lactam therapy.

BACKGROUND

This study investigated the molecular epidemiology, cross-resistance to novel antibiotics, and clonal distribution of carbapenem-resistant Pseudomonas aeruginosa (CRPA) clinical isolates.

METHODS

Forty-three CRPA isolates were collected from sterile clinical specimens in the Republic of Korea between 2015 and 2025. Susceptibility to 14 antibiotics was assessed in vitro by broth microdilution. Carbapenem-resistance mechanisms were characterized by using polymerase chain reaction, real-time quantitative reverse transcription polymerase chain reaction, and sequencing. Clonal diversity and epidemiological trends were examined by multilocus sequence typing.

RESULTS

Among the 43 CRPA isolates, the susceptibility rates were 88.4% for both aztreonam-avibactam and cefiderocol, compared with 46.5% for ceftolozane-tazobactam and 39.5% for ceftazidime-avibactam. Among the 22 difficult-to-treat resistance P. aeruginosa isolates, susceptibility rates were 77.3% for aztreonam-avibactam and 86.4% for cefiderocol. Carbapenemase genes were detected in 46.5% of isolates, predominantly blaNDM (41.9%). Porin loss and efflux pump overexpression were observed in 83.7% and 23.3% of isolates, respectively. Among the 22 P. aeruginosa isolates non-susceptible to both ceftolozane-tazobactam and ceftazidime-avibactam, 90.9% and 77.3% remained susceptible to aztreonam-avibactam and cefiderocol, respectively. Multilocus sequence typing identified 12 sequence types (STs), with predominance of ST773 and ST644, both carrying blaNDM.

CONCLUSIONS

CRPA exhibited multifactorial resistance driven by oprD disruption and blaNDM carriage within a diverse clonal structure dominated by ST773 and ST644. Aztreonam-avibactam and cefiderocol showed promising activity, supporting their role as critical therapeutic options.