Molecular epidemiological association between antimicrobial resistance characteristics and type III secretion system in carbapenem-resistant Pseudomonas aeruginosa from lower respiratory tract infections.

OBJECTIVE: Objective: This study investigated the antimicrobial resistance profile of carbapenem-resistant Pseudomonas aeruginosa (CRPA) and its association with the T3SS, aiming to provide evidence for managing highly resistant and virulent CRPA and to guide the optimization of infection control strategies.

METHODS: Retrospective cohort study was performed with CRPA lower respiratory tract infection from a tertiary hospital (July, 2021, and May, 2025). All strains underwent whole-genome sequencing (WGS), antimicrobial susceptibility testing(AST); selected isolates' virulence were further evaluated using galleria mellonella infection assays.

RESULTS: Among 106 patients caused by CRPA infections, the majority were male (73.6%), with a median age of 69.5 years and median hospital stay of 26.5 days. Prior antibiotic exposure included piperacillin/tazobactam (57.5%) and carbapenems (49.1%). AST revealed high resistance to piperacillin/tazobactam, but favorable susceptibility to ceftazidime/avibactam and tobramycin, with no polymyxin B resistance. Multidrug resistance occurred in 49.1% of isolates, and 28.3% were difficult-to-treat Pseudomonas aeruginosa (DTR-PA). The exoU and exoS genes were detected in 28.3% and 64.2% of strains, respectively, with 7.5% co-detection. ExoU+/exoS- strains showed significantly higher resistance to ceftazidime, cefepime, and piperacillin/tazobactam. All isolates had oprD mutations. Carbapenemase genes were found in 21.7%, primarily bla KPC-3. ExoU+/exoS- strains were linked to blaKPC-3 and bla OXA-50 subtypes(OXA-488,OXA-1032), while exoU-/exoS+ strains associated with blaOXA-486 and blaOXA-904 . Among 59 sequence types, ST1076 (13.2%) and ST491 (10.4%) dominated, with serotypes O11 (38.7%) and O6 (25.5%) prevalent. Six international high-risk clones included ST233, ST244, and ST357. Phylogenetically, phylogroup A (exoU-/exoS+, e.g., PAO1) was larger, and phylogroup B (exoU+/exoS-, e.g., PA14) included highly virulent strains. ExoU+/exoS- strains grouped in ST1076 and ST357, and exoU+/exoS+ in ST463. The survival of galleria mellonella further indicated that carrying the exoU may cause a higher lethality rate.

CONCLUSIONS: ExoU+/exoS- strains were strongly associated with resistance genes like bla KPC-3,bla OXA-488, bla OXA-1032, ICU admission and exhibited a more pronounced drug-resistant phenotype. Potential high-risk clones such as ST1076-O11 and ST463-O4 display both extensive resistance and high virulence, underscoring the clinical and public health importance of enhanced surveillance and effective containment.