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The essential oils obtained by hydrodistillation from fresh leaves of Cymbopogon citratus and Ocimum gratissimum growing in Cameroon were analyzed by GC and GC/MS. The main constituents of the oil of Ocimum gratissimum were gamma-terpinene (21.9 %), beta-phellandrene (21.1 %), limonene (11.4 %) and thymol (11.2 %), while the oil of Cymbopogon citratus contained geranial (32.8 %), neral (29.0 %), myrcene (16.2 %) and beta-pinene (10.5 %). The effects of these oils on the growth of Plasmodium berghei were investigated. Both oils showed significant antimalarial activities in the four-day suppressive in vivo test in mice. At concentrations of 200, 300 and 500 mg/kg of mouse per day, the essential oil of C. citratus produced the highest activity with the respective percentages of suppression of parasitaemia: 62.1 %, 81.7 % and 86.6 %. The corresponding values for the oil of O. gratissimum at the same concentrations were 55.0 %, 75.2 % and 77.8 %, respectively. Chloroquine (10 mg/kg of mouse, positive control) had a suppressive activity of 100 %.

The essential oils obtained by hydrodistillation of resins of Boswellia neglecta, B. pirottae, B. rivae, Commiphora myrrha (myrrh) and C. guidottii (opopanax or scented myrrh) were analysed using GC-MS. α-Thujene (19.2%), α-pinene (16.7%) and terpinen-4-ol (12.5%) were found to be the major components in B. neglecta; limonene (14.8%) in B. rivae; trans-verbenol (15.5%) and terpinen-4-ol (14.6%) in B. pirottae; (E)-β-ocimene (33%) in gum opopanax and furanoeudesma-1,3-diene (34%) in myrrh.

Aims:  The in vitro antimicrobial activity of three essential oil samples of frankincense (Boswellia rivae, Boswellia neglecta and Boswellia papyrifera) and two essential oil samples of myrrh and sweet myrrh (Commiphora guidotti and Commiphora myrrha), collected from different regions of Ethiopia, was investigated independently and in combination to determine their anti‐infective properties. Methods and Results:  The microdilution minimum inhibitory concentration (MIC) assay was performed, whereby it was noted that generally Cryptococcus neoformans (MIC values in the range of 0·8–1·4 mg ml−1) and Pseudomonas aeruginosa (MIC values in the range of 0·5–1·3 mg ml−1) often appeared to be the most susceptible micro‐organisms against oils of both Boswellia and Commiphora spp. When assayed in various combinations, the frankincense and myrrh oils displayed synergistic, additive and noninteractive properties, with no antagonism noted. When investigating different ratio combinations against Bacillus cereus, the most favourable combination was between B. papyrifera and C. myrrha. The composition of the oils was determined by gas chromatography coupled to mass spectrometry (GC–MS) to document the specific chemotypes used in the study, and the chemical profiles were found to be congruent with previously reported data. Conclusions:  The majority of interactions identified synergistic and additive effects, with strong synergism noted between B. papyrifera and C. myrrha. Significance and Impact of the Study:  Frankincense and myrrh essential oils have been used in combination since 1500 bc; however, no antimicrobial investigations have been undertaken to confirm their effect in combination. This study validates the enhanced efficacy when used in combination against a selection of pathogens.