Background: Streptococcus mutans and Candida albicans are major microorganisms implicated in dental caries and oral candidiasis. Although chlorhexidine is considered the gold standard for chemical plaque control, its long-term use is associated with several adverse effects, prompting interest in natural antimicrobial alternatives. This study aimed to compare the in vitro antimicrobial activity of Mentha longifolia essential oil with chlorhexidine against these two clinically important oral pathogens.

Methods: Standard strains of Streptococcus mutans (PTCC 1683) and Candida albicans (PTCC 10231) were evaluated in this in vitro experimental study. The minimum inhibitory concentration (MIC), minimum bactericidal/fungicidal concentration (MBC/MFC), and microbial killing time of Mentha longifolia essential oil and 0.2% chlorhexidine mouthwash were determined using the broth microdilution method.

Results: Chlorhexidine exhibited markedly lower MIC and MBC/MFC values than Mentha longifolia essential oil against both microorganisms, indicating greater antimicrobial efficacy at lower concentrations. However, differences were observed in their killing kinetics. Against Candida albicans, the essential oil achieved complete fungal elimination within 1 hour, whereas chlorhexidine required 24 hours despite its superior activity at lower concentrations. Against Streptococcus mutans, both agents completely eliminated bacterial growth within 5 hours.

Conclusion: Although chlorhexidine demonstrated greater antimicrobial potency at substantially lower concentrations, Mentha longifolia essential oil showed considerable antimicrobial activity, particularly a rapid fungicidal effect against Candida albicans. These findings suggest that Mentha longifolia essential oil may serve as a promising natural adjunct for the management of oral microbial infections. Further in vivo and clinical studies are required to confirm its therapeutic potential.