The emergence of pan-drug-resistant Pseudomonas aeruginosa in Iran: A genomic and phenotypic analysis of clinical isolates, multifactorial resistance mechanisms, and its societal impact.

BACKGROUND

Pseudomonas aeruginosa is a leading cause of healthcare-associated infections, with multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan-drug resistant (PDR) strains posing a severe global threat. This study aimed to analyze the genomic, phenotypic and multifactorial resistance mechanisms in clinical P. aeruginosa isolates from Iran.

METHODS

From April 2023 to January 2025, 364 non-duplicate P. aeruginosa isolates were collected from major tertiary and referral hospitals in 15 Iranian cities.

RESULTS

Antimicrobial susceptibility testing revealed high resistance to fluoroquinolones (65.9%) and carbapenems (47.2%), while colistin remained most effective (95.6% susceptibility). Among the isolates, 41% were MDR, 25% XDR, and 4.4% PDR. Phenotypic assays showed that 73.8% of carbapenem-resistant isolates produced metallo-β-lactamase (MBL), and 85.2% were biofilm producers, with a significant association between biofilm formation and MDR phenotype (p < 0.05). Efflux pump activity, detected in 28.9% of ciprofloxacin-resistant isolates, was prominent in all PDR strains. Genotypic analysis identified bla TEM (75.7%), bla CTX-M (50.3%), and bla NDM (43.6%) as the most prevalent ESBL and MBL genes. Mutation analysis in PDR isolates revealed non-synonymous substitutions in the mexB gene and a nonsense mutation in oprD, coupled with overexpression of MexAB-OprM efflux pump genes and underexpression of oprD. Plasmid analysis indicated that bla NDM was primarily carried on IncP and IncA/C replicons. Multilocus sequence typing identified high-risk clones ST357, ST175, and ST664.

CONCLUSION

This study underscores the critical convergence of multiple resistance mechanisms (enzymatic degradation, efflux overexpression, porin loss, and biofilm formation) driving the emergence of PDR P. aeruginosa in Iran, necessitating enhanced surveillance and innovative treatment strategies.