Determination of antimicrobial activity of Niaouli Essential Oil (Melaleuca quinquenervia) by two different methods; [Nioli Esansiyel Yağının (Melaleuca quinquenervia) antimikrobiyal aktivitesinin iki farklı yöntemle belirlenmesi]

Objective: This study aimed to investigate the antimicrobial activity of Niaouli Essential Oil (Melaleuca quinquenervia), a commercially available oil known for its antiseptic, antimicrobial, antioxidant, anti-inflammatory, and antiprotozoal properties due to its bioactive constituents, against eight different standard bacterial strains, two standard yeast strains, and one clinical Candida isolate. Methods: The antimicrobial activity of niaouli essential oil against the isolates was evaluated using the disk diffusion and broth microdilution methods in accordance with EUCAST and CLSI guidelines. Ten of the microbial strains were American Type Culture Collection (ATCC) strains, and one was a clinical Candida auris isolate. The isolates were obtained from the strain collection of our university. Results: In this study, the disk diffusion method revealed that niaouli essential oil (Melaleuca quinquenervia) was most effective against Staphylococcus aureus (20 ± 0.0 mm) and Streptococcus pneumoniae (17.3 ± 0.57 mm) among the bacterial strains, and against Candida albicans (20.6 ± 0.57 mm) among the fungal strains. The Candida auris isolate exhibited an inhibition zone of 16.0 ± 1.0 mm. The lowest MIC values determined by the broth microdilution method were 62.5 μg/mL for both S. aureus and C. albicans. Among the Gram-negative isolates, Klebsiella pneumoniae was the most susceptible (125 μg/mL), whereas Pseudomonas aeruginosa, Salmonella enteritidis, and Enterococcus faecalis were the least susceptible (>250 μg/mL). The MIC value for C. auris was determined to be 250 μg/mL, which is one dilution higher than the positive control (fluconazole: 125 μg/mL). Conclusion: Niaouli essential oil demonstrated antimicrobial activity against standard microbial strains, with varying levels of antibacterial and antifungal effects. According to both methods used, it was more effective against Gram-positive bacteria and fungi than Gram-negative bacteria. While it was particularly effective against Candida albicans among the yeasts, it also exhibited antimicrobial activity against the increasingly important Candida auris strain. Due to the increasing resistance to antibacterial and antifungal agents, further studies investigating alternative treatment options are needed. © 2026, Refik Saydam National Public Health Agency (RSNPHA). All rights reserved.