Evaluation of the combined efficacy of carvone and colistin against colistin-resistant Pseudomonas aeruginosa : in vitro and in vivo studies

ABSTRACT Pseudomonas aeruginosa ( P. aeruginosa ) is the primary pathogenic bacterium causing nosocomial-acquired infections, particularly in immunocompromised individuals. Owing to the abuse of colistin (COL), a frontline drug in clinical settings, the resistance rate of P. aeruginosa to COL has been escalating year by year, exerting a severe impact on public health. To solve this clinical problem, new therapeutic approaches are urgently required. This study initially proposes a strategy of using carvone in combination with COL to combat colistin-resistant Pseudomonas aeruginosa (COL-R P. aeruginosa ). The checkerboard assay and time-kill assay validated the in vitro antibacterial action of this combination against COL-R P. aeruginosa . Furthermore, crystalline violet staining and scanning electron microscopy (SEM) confirmed that the combined treatment effectively inhibited biofilm formation. Moreover, the thigh infection model in neutropenic mice showcased the in vivo effectiveness of the combined therapy. In addition, the erythrocyte hemolysis experiment and the in vivo safety assessment revealed that the combination of carvone and COL exhibited a certain level of safety at effective concentrations. The synergistic antibacterial and antibiofilm mechanisms of carvone combined with COL may be associated with the inhibition of quorum-sensing gene expression, enhancement of bacterial inner and outer membrane permeability, and increased generation of reactive oxygen species. This study offered a new therapeutic strategy for COL-R P. aeruginosa infections. IMPORTANCE The increasing prevalence of colistin-resistant Pseudomonas aeruginosa (COL-R P. aeruginosa ) poses a significant threat to global public health, as it limits treatment options for severe infections. This study investigates the synergistic effects of carvone, a natural compound, combined with colistin (COL) to combat COL-R P. aeruginosa both in vitro and in vivo . The findings reveal that carvone can restore the susceptibility of COL-R P. aeruginosa to COL. By exploring this novel combination, the research aims to provide a potential alternative therapeutic strategy for COL-R P. aeruginosa infections. The findings could pave the way for new approaches to treat infections caused by this resilient pathogen.