The essential oil of Helichrysum italicum significantly reduces the multidrug resistance of Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. Combinations of the two most active fractions of the essential oil with each other or with phenylalanine arginine ␤-naphthylamide yield synergistic activity. Geraniol, a component of one fraction, significantly increased the efficacy of ␤-lactams, quinolones, and chloramphenicol.

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A commercial sample of the essential oil of Chenopodium ambrosioides L. from Madagascar was analysed by GC, GC-MS and 13C-NMR. By GC analysis, the major constituents were found to be ascaridole (1) (41.8%), isoascaridole (2) (18.1%), p-cymene (16.2%), alpha-terpinene (9.7%) and limonene (3.8%). However, ascaridole undergoes a partial thermal isomerisation to 2 and hence the amount of 1 is under-estimated by GC analysis. The actual contents of 1 and 2 (55.3 and 4.6%, respectively) were obtained following combined analysis of the sample by GC and 13C-NMR. Several hydroxy- and polyhydroxy-menthanes were identified by 13C-NMR.

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The composition of the essential oil of Teucrium polium subsp. capitatum from Corsica was investigated using a combination of GC-RI, GC-MS (EI and CI) and 13 C-NMR spectroscopy after fractionation by column chromatography. The 86 identified compounds accounted for 93% of the total amount of the oil. The main components were α α α α α-pinene (28.8%), β β β β β-pinene (7.2%) and p-cymene (7.0%).

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The essential oils of six Helichrysum species from Madagascar were investigated and 46 components were identified by GC, GC-MS and 13 C-NMR spectrometry. The main constituents were 1,8-cineole for H. gymnocephalum (59.7%) and H. bracteiferum (27.3%);ˇ-pinene for H. selaginifolium (38.2%); (E)-caryophyllene for H. cordifolium (55.6%), H. faradifani (34.6%) and H. hypnoides (34.0%).