Evaluation of the antimicrobial and antibiofilm activity of Quercus coccifera plant leaf extract against Gram-positive and Gram-negative bacteria.

Abstract

Background and aim: The escalating global threat posed by antimicrobial resistance has intensified the search for novel antimicrobial agents. Plant-derived bioactive compounds represent a promising reservoir due to their chemical diversity and efficacy against resistant pathogens. Quercus species, traditionally utilized in herbal medicine, have shown significant bioactive potential. However, research specifically evaluating the antimicrobial and antibiofilm properties of Quercus coccifera remains limited. This study aimed to investigate the phytochemical composition, antimicrobial, antibiofilm, and antioxidant activities of Q. coccifera leaf extracts using various extraction methods and solvents with differing polarities.

Materials and methods: Q. coccifera leaves were harvested, dried, and extracted using solvents of varying polarity (n-hexane, chloroform, methanol, boiled water, and microwaved water). Phytochemical profiling included tests for alkaloids, tannins, glycosides, and terpenoids. Antioxidant activity was assessed using the DPPH assay. Antimicrobial activities against Gram-positive (Staphylococcus aureus and Streptococcus pneumoniae) and Gram-negative (Pseudomonas aeruginosa, Escherichia coli, and Brucella melitensis) bacteria were evaluated using AlamarBlue® (Invitrogen, Glasgow, UK) assay and Minimum Inhibitory Concentration (MIC) determination. Antibiofilm activity was assessed by biofilm viability tests and Minimum Biofilm Eradication Concentration (MBEC) assays.

Results: Methanolic and boiled water extracts demonstrated robust phytochemical profiles (alkaloids, tannins, glycosides, and terpenoids) and significant antioxidant activity (>90% inhibition). Antimicrobial pre-evaluation indicated superior antibacterial efficacy (>90% inhibition) of these extracts, while microwaved water extracts showed moderate activity (~75% inhibition). The methanolic and boiled water extracts exhibited potent antimicrobial effects with MIC values <30 μg/mL against all tested pathogens except S. pneumoniae. Similarly, these extracts effectively disrupted biofilms formed by S. aureus and P. aeruginosa, with MBEC values approximately 25 μg/mL.

Conclusion: Polar solvent extracts of Q. coccifera leaves exhibit significant antimicrobial and antibiofilm activities, underlining their potential as novel antimicrobial agents or adjuncts to existing therapies. Future studies involving cytotoxicity evaluation and in vivo efficacy are essential to translate these findings into clinical applications.