Activity of Six Essential Oils Extracted from Tunisian Plants against Legionella pneumophila

Abstract

The aim of this study was to investigate the composition of six essential oils extracted from Tunisian plants, i.e., Artemisia herba-alba Asso, Citrus sinensis (L.) Osbeck, Juniperus phoenicea L., Rosmarinus officinalis L., Ruta graveolens L., and Thymus vulgaris L., and to evaluate their activity against Legionella pneumophila (microdilution assays). Eight Legionella pneumophila strains were studied, including the two well-known serogroup 1 Lens and Paris strains as controls and six environmental strains isolated from Tunisian spas belonging to serogroups 1, 4, 5, 6, and 8. The essential oils were generally active against L. pneumophila. The activities of the A. herba-alba, C. sinensis, and R. officinalis essential oils were strain-dependent, whereas those of the J. phoenicea and T. vulgaris oils, showing the highest anti-Legionella activities, with minimum inhibitory concentrations (MICs) lower than 0.03 and lower than or equal to 0.07 mg/ml, respectively, were independent of the strains' serogroup. Moreover, the microorganisms treated with T. vulgaris essential oil were shorter, swollen, and less electron-dense compared to the untreated controls. Isoborneol (20.91%), (1S)-α-pinene (18.30%) β-phellandrene (8.08%), α-campholenal (7.91%), and α-phellandrene (7.58%) were the major components isolated from the J. phoenicea oil, while carvacrol (88.50%) was the main compound of the T. vulgaris oil, followed by p-cymene (7.86%). This study highlighted the potential interest of some essential oils extracted from Tunisian plants as biocides to prevent the Legionella risk.

Thymbra capitata (L.) Cav. and Rosmarinus officinalis (L.) Essential Oils: In Vitro Effects and Toxicity on Swine Spermatozoa

“…Due to its relatively wider “safety window”, the EO of R. officinalis may be exploited, in reproductive medicine, for its antioxidant and antibacterial effects. For instance, Chaftar et al [ 26 ] reported that the minimum inhibitory concentration (MIC) of this EO against several strains of Legionella pneumophila is <0.55 mg/mL, a concentration that, according to the present study, would be well tolerated by spermatozoa. Further studies are necessary to confirm its potential as an antibacterial agent, for example, in artificial insemination swine doses, where antibiotics are still mandatory [ 13 ].…”

Artemisia arborescens Essential Oil Composition, Enantiomeric Distribution, and Antimicrobial Activity from Different Wild Populations from the Mediterranean Area

“…arborescens EO . Nonetheless, such effect could also depend on other compounds including α ‐pinene, 1,8‐cineole, borneol, and thymol or the enantiomeric distribution of some compounds, as also found by Tabanca et al . , whereas few or no inhibitory activity could be attributed to chamazulene and germacrene D, which are likely active against fungi and Gram ‐positive bacteria .…”

Legionella pneumophila: The Paradox of a Highly Sensitive Opportunistic Waterborne Pathogen Able to Persist in the Environment

“…More recently, results obtained by Chaftar et al, 2015a , b ), have highlighted the anti- Legionella activity of essential oils extracted from Tunisian plants. Oils extracted from Juniperus phoenicea and Thymus vulgaris exhibited the highest anti- L. pneumophila activity, with MICs lower than 0.03 mg/ml and lower than 0.07 mg/ml, respectively.…”

“…Indeed, EOs can act by degrading the cell wall ( Helander et al, 1998 ), inducing damages to the cytoplasmic membrane ( Ultee et al, 2002 ) and to membrane proteins ( Ultee et al, 1999 ), causing the leakage of cell contents ( Lambert et al, 2001 ), coagulating the cytoplasm ( Gustafson et al, 1998 ) and depleting the proton motive force ( Ultee and Smid, 2001 ). To date, only Chaftar et al (2015b) have investigated EOs action against L. pneumophila . Indeed, scanning electron microscopy analysis highlighted morphological alterations of bacteria when treated with T. vulgaris EO as cells appeared shorter, flattened, and expanded compared to the untreated ones.…”

“… Anti- Legionella activity of Thymus vulgaris EO observed by transmission electron microscopy. Micrographs of (A) untreated control cells of L. pneumophila Lens strain and (B) treated L. pneumophila Lens with 70 μg/ml Thymus vulgaris EO (Source: Chaftar et al, 2015b ). …”