Emergence of a multidrug-resistant Pseudomonas fulva clinical isolate co-harboring tmexCD3–toprJ3, blaOXA-1, and blaIMP-45 on a transferable megaplasmid

Introduction Pseudomonas fulva is a non-fermentative bacterium with both environmental adaptability and pathogenic potential that has been increasingly detected in clinical infections in recent years. This study reports the first clinical P. fulva (PF1) isolate carrying tmexCD3-toprJ3 , bla OXA-1 , and bla IMP-45 resistance genes, which was recovered from the urine of a patient with a urinary tract infection. Methods Species identification was performed using whole-genome sequencing and average nucleotide identity analysis, with phylogenetic placement determined by 16S rRNA. Genomic analysis identified resistance genes and plasmid structures, while plasmid transferability was assessed experimentally. Biofilm formation, stress tolerance, and virulence were evaluated using crystal violet staining, stress assays, and the Galleria mellonella model. Results PF1 exhibited resistance to carbapenems, cephalosporins, quinolones, and an elevated tigecycline MIC of 256 mg/mL, while remaining susceptible to polymyxins. The strain harbors a 449-kb transferable megaplasmid (pPF1), containing resistance genes bla IMP-45 , bla OXA-1 , and a mutated tmexCD3-toprJ3 efflux pump(T1827G and T1830C). Phylogenetic analysis showed >99% genomic similarity to clinical isolates from eastern China. PF1 demonstrated strong biofilm formation (OD620 = 3.73 ± 0.14), stress tolerance, and moderate virulence in Galleria mellonella . Discussion This study reveals the potential of P. fulva to acquire multidrug resistance and adapt to clinical environments, underscoring the need for enhanced surveillance of resistance genes in atypical Pseudomonas species.