Association of the exoU genotype with a multidrug non-susceptible phenotype and mRNA expressions of resistance genes in Pseudomonas aeruginosa.

The increased prevalence of the virulence factor exoU + genotype among multidrug-resistant Pseudomonas aeruginosa has been previously reported. However, the genes that are related to the multidrug resistance of the exoU + genotype strain have not been analyzed and remain to be elucidated. The objective of this study was to analyze the correlations between virulence factors and resistance genes. The exoU + genotype was frequently found in carbapenem and fluoroquinolone non-susceptible strains. The imp carbapenemase genotype, the quinolone-resistance-determining region mutation in GyrA and ParC and the defective mutation in OprD were not frequently found in the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. On the other hand, mexY and ampC mRNA overexpressing strains were more frequently found in the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. Moreover, sequence type 235, a high risk clone of multidrug-resistant P. aeruginosa, was prevalent among the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. ExoU is highly virulent protein, and the overexpression of efflux pumps and AmpC β-lactamase induce a multidrug-resistant phenotype. Therefore, the increased prevalence of P. aeruginosa strains with an exoU + genotype and the overexpression of efflux pumps and AmpC β-lactamase are likely to make P. aeruginosa infections difficult to treat. An understanding of the prevalence of both the exoU + genotype and the mRNA overexpression of resistance genes may help to select empirical therapy for the treatment of nosocomial infections caused by P. aeruginosa.