Evaluating the anti-biofilm and antibacterial effects of Juglans regia L. extracts against clinical isolates of Pseudomonas aeruginosa

Objective: Pseudomonas aeruginosa, an opportunistic pathogen, can cause serious health problems and produces several virulence factors. The most important of these factors is biofilm. Many studies suggest administration of new generation of antibiotics, as P. aeruginosa biofilm has developed high resistance to antimicrobial drugs. Emergence of multidrug resistant (MDR) strains has resulted in screening biofilm inhibitors from natural products or modified from natural compounds. To test this hypothesis, we evaluated the inhibitory effects (antibacterial and antibiofilm) of Juglans regia L. extract on biofilm formation by clinical isolates of P. aeruginosa.

Methods: Samples collected from burn, tracheal and urine infections of hospitalized patients (Shahid Motahari Hospital, Tehran, Iran) were identified as P. aeruginosa using traditional biochemical tests. Antibiotic susceptibility testing of isolates was performed using disk diffusion method. The microtiter plate method was used to evaluate the ability of pathogenic strains in producing biofilm. Antibacterial and antibiofilm effects of aqueous and methanol Juglans regia L. leaf extracts were determined by microtiter plate method.

Results: 46.7% of P. aeruginosa isolates (n = 50) were resistant to gentamicin and 100% of them could form a biofilm. All isolates (100%) exhibited MDR phenotype. Various concentrations of Juglans regia L. extracts exhibited significant effects on the growth and biofilm inhibition of the isolates. In addition, aqueous Juglans regia L. leaf extract had better inhibition activity on planktonic growth, and methanol extract was more effective on inhibiting biofilm of P. aeruginosa.

Conclusions: The results of this study indicate that antibiotic-resistant strains were significantly associated with biofilm formation. The J. regia L. extract, at various concentrations, may provide an alternative to control biofilm-related infections caused by P. aeruginosa. Further analyses are needed to validate the antibiofilm activity of these medicinal plants.