Peel and leaf oils of 43 taxa of lemons and limes were obtained from fruits and leaves collected from trees submitted to the same pedoclimatic and cultural conditions. Their chemical composition was investigated by capillary GC, GC-MS, and (13)C NMR, and the results were submitted to principal component analysis to check for chemical variability. Three major chemotypes were distinguished for lemon peel oils: limonene; limonene/beta-pinene/gamma-terpinene; and limonene/linalyl acetate/linalool. Two chemotypes were identified for lemon leaf oils: limonene/beta-pinene/geranial/neral and linalool/linalyl acetate/alpha-terpineol. In lime peel oils, four chemotypes were distinguished: limonene; limonene/gamma-terpinene; limonene/beta-pinene/gamma-terpinene; and limonene/gamma-terpinene/beta-pinene/oxygenated products. Four others were identified for lime leaf oils: beta-pinene/limonene; limonene/geranial/neral; limonene/linalool/citronellal; and limonene/sabinene/citronellal/linalool. These results were interpreted using principal component analysis.

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Peel and leaf oils of 30 sour orange cultivars, belonging to four different species (C. aurantium L., C. myrtifolia Raf., C. natsudaidai Hay. and C. neo‐aurantium Tan.) were obtained from fruits and leaves collected on sour orange trees submitted to the same pedoclimatic and horticultural conditions. Their chemical composition was investigated by capillary GC, GC–MS and 13C‐NMR. Two chemotypes, limonene and limonene/β‐pinene, were distinguished for peel oils, while four chemotypes, linalool/linalyl acetate, sabinene/(E)‐β‐ocimene, limonene/β‐pinene and β‐pinene/linalool, were observed for leaf oils. Copyright © 2001 John Wiley & Sons, Ltd.

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Quorum sensing (QS) is a bacterial communication mechanism used to express various survival or virulence traits leading to enhanced resistance. Chromobacterium violaceum is a commonly used strain that highlights anti-QS action of bioactive substances. Here, we wanted to see if 12 selected essential oils (EO) could exert anti-QS activity. We measured the sublethal minimal QS inhibitory concentration (MQSIC) by assessing violacein production of C. violaceum along with bacterial growth. To confirm the QS disruption, we also proceed to surface bacterial observations using scanning electron microscopy (SEM). We showed that cis-cis-p-menthenolide extracted and isolated from a plant endemic to occidental Mediterranean Sea islands, Mentha suaveolens ssp. insularis, acts as an inhibitor of violacein production and biofilm formation. Measured MQSIC was much lower than the minimal inhibitory concentration (MIC): 0.10 mg·mL−1 vs. 3.00 mg·mL−1. Moreover, disturbance of QS-related traits was confirmed by the degradation of C. violaceum biofilm matrix. There is a clear structure–activity relationship between cis-cis-p-menthenolide and anti-QS activity. Indeed, its isomer molecule (mintlactone) exerts a poor anti-QS action. These results indicate that inhibition of violacein production and biofilm formation by cis-cis-p-menthenolide might be related to a disruption in the QS mechanism.

The purpose of this study was to investigate the primary mode of action of Cistus ladaniferus essential oil active fractions on Staphylococcus aureus strain ATCC6538P (CIP 53.156). The mode of inhibition of the active fractions was assessed by determining the minimum inhibitory concentration (MIC). The effects of time on cell integrity were determined by time-kill, bacteriolysis and loss of 260 and 280-nm-absorbing material assays. Measurement of intra-and extracellular ATP was used to evaluate the energy remaining in the cells after treatment. A bacteriostatic and a bactericidal mode of inhibition were established respectively for acetate and alcohol fractions at their MIC. No intracellular material leakage and no lysis occurred after treatments with these fractions. In both cases, we observed a decrease of the ATP level within S. aureus cells whilst there was no proportional increase outside the cells. However, the effects induced by alcohols are more pronounced than those provoked by acetates. Indeed, marked structural changes were observed by transmission electron microscopy (TEM). The septal material of cells undergoing division became thicker and stained more lightly. The proportion of septa is also markedly increased and defective with respect to placement. These observations suggest a blocking in cell division, probably caused by the inhibition of ATPase or a disturbance in proton motrice force by the hydrophobic molecules viridiflorol and ledol, mainly present in alcohol fraction.