Terpinen-4-ol, the Main Bioactive Component of Tea Tree Oil, as an Innovative Antimicrobial Agent against Legionella pneumophila

• Published in: Pathogens (Basel) Vol. 11; no. 6; p. 682
• Main Authors: Mondello, Francesca, Fontana, Stefano, Scaturro, Maria, Girolamo, Antonietta, Colone, Marisa, Stringaro, Annarita, Vito, Maura Di, Ricci, Maria Luisa
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 14.06.2022; MDPI
• Subjects: anti-infective agents; antibacterial activity; antibacterial properties; Antiinfectives and antibacterials; Antimicrobial activity; Antimicrobial agents; Bacterial diseases; Bactericidal activity; bioactive compounds; Cell surface; Contamination; COVID-19; Cytology; Dilution; Disinfection; essential oil; Essential oils; Europe; Legionella pneumophila; Legionnaire's disease; Legionnaires' disease bacterium; Melaleuca alternifolia; Minimum inhibitory concentration; Morphology; pneumonia; Pollution control; Scanning electron microscopy; System effectiveness; tea; tea tree oil; Temperature; Temperature dependence; terpinen-4-ol; Terpinene; trees; Vapors; Warm water; Italy; Europe
• DOI: 10.3390/pathogens11060682
• ISSN: 2076-0817

Legionella pneumophila (Lp), responsible for a severe pneumonia called Legionnaires’ disease, represents an important health burden in Europe. Prevention and control of Lp contamination in warm water systems is still a great challenge often due to the failure in disinfection procedures. The aim of this study was to evaluate the in vitro activity of Terpinen-4-ol (T-4-ol) as potential agent for Lp control, in comparison with the essential oil of Melaleuca alternifolia (tea tree) (TTO. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of T-4-ol were determined by broth micro-dilution and a micro-atmosphere diffusion method to investigate the anti-Lp effects of T-4-ol and TTO vapors. Scanning Electron Microscopy (SEM) was adopted to highlight the morphological changes and Lp damage following T-4-ol and TTO treatments. The greatest antimicrobial activity against Lp was shown by T-4-ol with a MIC range of 0.06–0.125% v/v and MBC range of 0.25–0.5% v/v. The TTO and T-4-ol MIC and MBC decreased with increasing temperature (36 °C to 45 ± 1 °C), and temperature also significantly influenced the efficacy of TTO and T-4-ol vapors. The time-killing assay showed an exponential trend of T-4-ol bactericidal activity at 0.5% v/v against Lp. SEM observations revealed a concentration- and temperature- dependent effect of T-4-ol and TTO on cell surface morphology with alterations. These findings suggest that T-4-ol is active against Lp and further studies may address the potential effectiveness of T-4-ol for control of water systems.