Antibacterial activity of medicinal plants extracts; Rosmarinus officinalis and Nerium oleander

Bacterial resistance to antibiotics has led scientists to search into nature for novel therapeutic molecules with less or no side effects. This study aims to determine the antibacterial activity of methanol extract of the leaves and stems of two plants species widely used in traditional medicine in the Mediterranean basin; Rosmarinus officinalis and Nerium oleander. The antibacterial activity was evaluated through determining the minimum inhibitory concentration (MIC) by the agar dilution method on four microbial strains; Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus cereus. Results showed that extracts of the different parts of both species revealed inhibitory activity against all the tested strains with lower MICs exhibited by R. officinalis. P. aeruginosa was shown to be the most sensitive bacteria to N. oleander extracts and S. aureus the most resistant to them. However, E. coli was relatively the most resistant bacteria to R. officinalis extracts whereas B. cereus was the most sensitive to them. It should be noted that Gram-positive bacteria were the most sensitive to R. officinalis extracts while Gram-negative bacteria were more sensitive to N. oleander extracts. Taking all together, both plant species proved to be effective antibacterial agents and consequently, they may constitute a potential natural resource for new substances with antibacterial activity as alternative of the usual drugs to avoid microbial resistance.