Chemical composition analysis of essential oils of four plants from Aurès region of Algeria and their antibacterial and antibiofilm activities against coagulase-negative staphylococci

Background: The altitudinal and geographical variability of the Aurès mountains of Algeria favored the existence of some endemic and rare varieties of medicinal plants. The aim of the present work is to determine the chemical composition, antimicrobial and antibiofilm properties of the  essential oils (EOs) from aerial parts of four medicinal plants from Aurès region of Algeria; Juniperus thurifera L., Juniperus oxycedrus L., Salvia   officinalis L. and Thymus ciliatus ssp. munbyanus (Boiss. & Reut.) Batt. on coagulase negative staphylococci (CoNS) isolates. Methodology: Extraction of EOs from the four plant materials was carried out by hydro-distillation, and the EO yield expressed in gram of the distillate per 100 grams of dry matter. The chemical composition of the EOs was analyzed by gas chromatography-mass spectrometry (GC-MS) method. In vitro antibacterial and antibiofilm activities of the EOs were evaluated against CoNS previously isolated at the Anti-Cancer Center of Batna, Algeria using the agar disc diffusion assay and biofilm inhibition study, respectively. Minimum inhibitory concentration (MIC) and minimum  bacterial concentration (MBC) of the EOs of S. officinalis L. and T. ciliatus ssp. munbyanus were determined by the dilution method. Results: Twenty-seven and 41 compounds rich in monoterpene hydrocarbons were identified from J. oxycedrus and J. thurifera plants respectively, while 45 and 32 compounds, constituted mainly by oxygenated monoterpenes, were identified from S. officinalis L. and T. ciliatus ssp. munbyanus, respectively. The EOs of T. ciliatus ssp. munbyanus showed the most inhibitory activity of all the four plants on CoNS isolates (n=66) with mean  inhibition zone diameter of 24.99±6.29mm, and mean MIC and MBC values of 2.65±3.77mg/ml and 5.31±7.41mg/ml respectively, followed by S.  officinalis L., with mean inhibition zone diameter of 13.38± 6.52mm, and mean MIC and MBC values of 27.53±28.2 mg/ml and 31.97±33.19 mg/ml  respectively (p<0.0001 by one-way ANOVA). Also, percentage biofilm inhibition of CoNS isolates (n=59) was high for EOs of T. ciliatus ssp. munbyanus  (65.63±10.71%) and S. officinalis L. (53.13±5.83%), although was significantly higher for T. ciliatus ssp. munbyanus compared to S. officinalis L. (p<0.0001, t=7.874). Conclusion: Essential oils from T. ciliatus ssp. munbyanus and S. officinalis L. could represent an alternative to classical antibiotics against planktonic cells and biofilms of CoNS

Natural insecticides from native plants of the Mediterranean basin and their activity for the control of the date moth Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae)

The present work aims at evaluating the insecticidal activity of T. algeriensis and T. hyemalis (Lamiaceae) essential oils against different stages of Eceratoniae ceratoniae Zeller (Lepidoptera: Pyralidae) in controlled conditions. Essential oil vapours were isolated by hydrodistillation and analysed by gas chromatography-mass spectrometry technique (GC-MS). Camphor (37.29%), 1,8-cineole (11.12%), camphene (7.81%), myrcene (7.13%) and borneol (5.54%) were obtained as major compounds in the essential oil of T. algeriensis, while the main essential oil compounds of T. hyemalis were 1,8-cineole (34.17%), camphor (8.33%) and camphene (7.11%). Ovicidal activity of oils was studied by topical application, while the adulticidal and larvicidal activities were assessed by fumigation and ingestion. The results revealed that T. hyemalis oil was more effective as compared to T. algeriensis. The exposure to T. hyemalis vapour caused 0% of hatching rate at the concentration of 2.5 mg/ml, while at the same concentration, the hatching rate was 15% when eggs were exposed to T. algeriensis oil. The adulticidal activity of both oils decreased with the increase in concentration or exposure time. The corresponding LC50 values were found to be 0.11 and 0.19 mg/ml respectively for T. hyemalis and T. algeriensis. Young larvae L1 seemed to be more resistant to both essential oils in the antifeedant bioassay (LC50 = 2.75 mg/ml for T. hyemalis and 5.78 mg/ml for T. algeriensis). Overall, this work showed the efficacy of essential oils from plants of Mediterranean origin that could be used as an alternative to synthetic insecticides for the managing of E. ceratoniae