Objective: This study has been done to evaluate the interaction between water extracts of Psidium guajava, Rosmarinus officinalis, Salvia fruticosa, Majorana syriaca, Ocimum basilucum, Syzygium aromaticum, Laurus nobilis, and Rosa damascena alone and then synergy testing of these extracts with known antimicrobial agents including oxytetracycline HCl, gentamicin sulfate, penicillin G, cephalexin and enrofloxacin. This study was conducted against five S. aureus isolates; one is Methicillin-resistant Staphylococcus aureus (MRSA) and 4 Methicillin-sensitive Staphylococcus aureus (MSSA
Methods: Evaluation of the interaction between plant extracts and different antimicrobial agents has been done using well-diffusion and microdilution methods.
Results: The results of the conducted experiments using well-diffusion method demonstrate that these plants showed in vitro interactions between antimicrobial agents and plant extracts were additive, while using microdilution method showed synergistic effects with significant reduction in the MICs of the test antibiotics against these strains of S. aureus. This change in MIC was noticed in all plant extracts including these plants showed weak antibacterial activity by well diffusion method. Synergism effect was occurred in both sensitive and resistant strains but the magnitude of minimum fold reduction of inhibitory concentration in resistant strains especially MRSA strain was higher than the sensitive strains.
Coclusion: This study probably suggests the possibility of concurrent use of these antimicrobial drugs and plant extracts in combination in treating infections caused by S. aureus strains or at least the concomitant administration may not impair the antimicrobial activity of these antibiotics.