Evaluation of Antimicrobial and Antibiofilm Effects of Almond (Prunus amygdalus) Green Skin Extract on Pseudomonas aeruginosa and Staphylococcus aureus Isolates

Abstract

Introduction: Given the emergence of antibiotic-resistant bacteria and the therapeutic potential of plant extracts against various bacterial strains, this study aims to investigate the antimicrobial, antibiofilm, and combined antibiotic effects of lyophilized almond (Prunus amygdalus) green skin extract on both clinical and standard isolates of Pseudomonas aeruginosa and Staphylococcus aureus.Method: This study examined the antimicrobial and antibiofilm effects of almond green skin extract on standard strains of P. aeruginosa (ATCC 27853) and S. aureus (resistant ATCC 25923), along with 20 clinical isolates (10 of each strain). Iranian almond green skin was collected, dried, and prepared for extraction. High-performance liquid chromatography (HPLC) was used to identify and quantify the phenolic compounds in the extract. A checkerboard assay was performed to evaluate the effects of combining antibiotics with the lyophilized almond green skin extract. The antibiofilm assay was conducted for each compound individually and in combination, at various concentrations. The MTT assay was used to assess the cytotoxic effects of the lyophilized extract.Results: The minimum inhibitory concentration (MIC) values for cefoxitin, meropenem, and the almond green skin extract were found to be 1-128 mu g/mu L, 0.25-32 mu g/mu L, and 8-16 mg/mL, respectively. Additionally, checkerboard results for the extract combined with the antibiotic meropenem on clinical isolates of P. aeruginosa showed an additive effect in five isolates and a synergistic effect in another five. The highest biofilm inhibition rate of cefoxitin alone on MDR S. aureus isolates was observed at a concentration of 2xMIC (16 mu g/mL), with 95 inhibition. MTT results indicated that the lowest cell viability (84) occurred at a concentration of 64 mu g/mu L of cefoxitin with 0.512 mg/mL of the extract, while the highest cell viability (94) was observed at 25 mu g/mu L of cefoxitin with 0.512 mg/mL of the extract.Conclusion: The combination of antibiotics with almond green skin extract enhances bactericidal and antibiofilm properties against clinical isolates of S. aureus and P. aeruginosa.