| Summary: | The chemical composition of the volatile oils from five Anacardiaceae species and their activities against Gram positive and negative bacteria were assessed. The peroxidative damage within bacterial cell membranes was determined through the breakdown product malondialdehyde (MDA). The major constituents in <em>Anacardium</em> <em>humile</em> leaves oil were (<em>E</em>)-caryophyllene (31.0%) and <em>α</em>-pinene (22.0%), and in <em>Anacardium occidentale</em> oil they were (<em>E</em>)-caryophyllene (15.4%) and germacrene-D (11.5%).<em> </em>Volatile oil from <em>Astronium fraxinifolium</em> leaves were dominated by (<em>E</em>)-<em>β</em>-ocimene (44.1%) and <em>α</em>-terpinolene (15.2%), whilst the oil from <em>Myracrodruon urundeuva</em> contained an abundance of <em>δ</em>-3-carene (78.8%). However, <em>Schinus terebinthifolius</em> leaves oil collected in March and July presented different chemical compositions. The oils from all species, except the one from <em>A. occidentale</em>, exhibited varying levels of antibacterial activity against <em>Staphylococcus aureus</em>, <em>Bacillus cereus</em> and <em>Escherichia coli</em>. Oil extracted in July from <em>S. terebinthifolius </em>was more active against all bacterial strains than the corresponding oil extracted in March. The high antibacterial activity of the <em>M. urundeuva</em> oil could be ascribed to its high <em>δ</em>-3-carene content. The amounts of MDA generated within bacterial cells indicate that the volatile oils induce lipid peroxidation. The results suggest that one putative mechanism of antibacterial action of these volatile oils is pro-oxidant damage within bacterial cell membrane explaining in part their preservative properties.
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