Background: Quantitative and qualitative changes in the plant chemical profiles due to
stress-induced response may alter the biological activity of plant tissues. In the current study, we
tested the hypothesis that biologic potential against microorganisms of essential oils obtained from
Piper marginatum leaves may be affected by herbivore or mechanical injury.
Methods: The chemical compositions of the essential oils were determined by GC/MS while antimicrobial
activity was determined by disc diffusion method and minimum inhibitory concentration assay.
Results: The chemical profile of leaf essential oil of P. marginatum underwent alterations when infested
with the grasshopper Xyleus discoideus. The antimicrobial activity of leaf essential oil infested
by grasshopper decreased against the microorganisms Bacillus subtilis and Mycobacterium smegmatis,
and oil was inactive against the fungus Malassezia furfur. Additionally, the essential oil obtained
of P. marginatum leaves subjected to the mechanical damage showed chemical change compared to
the oil from the intact leaves but did not cause alterations in the antimicrobial activity of oil.
Conclusion: The overall results of this study reveal that P. marginatum leaves respond very clearly to
the damages caused by attack by the grasshopper X. discoideus and mechanical damage.