Harnessing anti-infective efficacy of Cinnamomum verum in synergy with β-lactam and fluoroquinolones drugs to combat virulence and biofilms of Pseudomonas aeruginosa PAO1.

Multidrug resistance (MDR) Gram-negative bacteria are increasingly resistant to multiple antibiotics, posing a serious challenge to infection control and treatment. Combining plant-derived bioactives with antibiotics offers a promising approach to overcome the challenges posed by MDR pathogens like Pseudomonas aeruginosa. This study investigated the synergistic effects of Cinnamomum verum with beta-lactam and fluoroquinolones against P. aeruginosa PAO1. The ethyl acetate fraction of C. verum (CVEF) was obtained through fractionation in organic solvents with progressively higher polarity. The interaction of CVEF with selected antibiotics was assessed by checkerboard synergy assay. The effects of synergistic combinations on pyocyanin, pyoverdine, protease, EPS production, and biofilm development were measured using spectroscopic assays. CVEF combined with cefepime, ceftazidime, and levofloxacin significantly enhanced antibacterial efficacy with FICIs between 0.156 and 0.5. The most active combinations i.e., CVEF-cefepime and CVEF-ceftazidime inhibited viable cell count of growth by 3.6 and 4.2 log CFU/ml respectively. The combination also inhibited virulence factors (>75 %) and biofilms (>80 %) at lower 1/2 × FICs. The viable count of biofilm cells was also reduced from 6.4 to 3.3 and 3.6 log CFU/ml. Membrane permeability was decreased by 60.34 % and biofilm cell viability by 22.53-38.44 %. Key phytochemicals analyzed by GC/MS and LC/MS/MS, include cinnamaldehyde, trans-chlorogenic acid, quercetin, and quercetin 3'-O-glucuronide. In molecular docking investigations, quercetin 3'-O-glucuronide had the highest binding affinity with quorum sensing (QS) and biofilm-associated protein. The findings suggest CVEF, in combination with antibiotics, effectively targets resistance phenotypes of P. aeruginosa, impairing growth, virulence, and biofilms. This supports further research into natural compounds alongside antibiotics to treat drug-resistant infections.