Antibacterial Activity of Quercus crassifolia Bonpl. Extracts against Periodontal Pathogens: A Potential Adjuvant Therapeutic Alternative for Periodontitis?

Introduction/Objective: This study evaluated the in vitro antimicrobial activity of hydroalcoholic (HA) and aqueous (AQ) extracts of Quercus crassifolia Bonpl. against periodontopathogenic bacteria, investigating the scientific basis for its traditional use in Mexico as a treatment for periodontitis. Methods: The antimicrobial activity of both extracts was assessed using the agar disc diffusion method (inhibition zones) and the minimum inhibitory concentration (MIC) to determine their inhibitory effects against periodontal bacteria (Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans serotype b, Fusobacterium nucleatum subsp. nucleatum, and Actinomyces israelii). Results: The hydroalcoholic (HA) extract produced significantly larger inhibition zones than the aqueous (AQ) extract against all tested periodontopathogenic strains. The most notable differences were observed against Aggregatibacter actinomycetemcomitans serotype b (HA: 18.7 ± 6.7 mm vs. AQ: 11.0 ± 1.0 mm) and Fusobacterium nucleatum subsp. nucleatum. (HA 11.3 ± 0.6 mm vs. AQ 9.7 ± 0.6 mm). The results for Porphyromonas gingivalis (HA: 11.0 ± 1.0 mm vs. AQ: 7.7 ± 1.2 mm) and Actinomyces israelii (HA: 9.0 ± 1.0 mm vs. AQ: 8.0 ± 1.0 mm). However, the HA extract was only statistically superior to the AQ extract against the latter species (p < 0.05). The HA extract also demonstrated greater potency in vitro, exhibiting a lower minimum inhibitory concentration (MIC) range (15.6 μg/mL) compared to the AQ extract (125 μg/mL). As expected, the 0.20% chlorhexidine (CHX) control showed stronger antimicrobial activity than both botanical extracts. Discussion: The antimicrobial potential of Q. crassifolia was strongly supported by its low Minimum Inhibitory Concentration (MIC) values and significant inhibition zones, suggesting a potent antibacterial effect. These MIC results are comparable to those reported for other potent oak species, which also exhibit low MICs against a broad spectrum of bacteria, including Staphylococcus aureus and Pseudomonas aeruginosa. Conclusion: The extracts of Quercus crassifolia Bonpl., particularly the HA extract, demonstrated significant antibacterial potential compared to the AQ extract, although its antimicrobial effect was less than that of 0.20% reactive-grade CHX. These results suggest that Q. crassifolia Bonpl. could serve as a natural adjunctive alternative for non-surgical periodontal treatment due to its antimicrobial potential against periodontal pathogens. This finding may support its ethnobotanical use. However, further in vivo and in vitro studies are required to substantiate its efficacy as an adjunctive treatment to non-surgical periodontal therapy for controlling periodontitis.