Middle-East Journal of Scientific Research 3 (3): 134-139, 2008 ISSN 1990-9233 © IDOSI Publications, 2008 Corresponding Author: Ghaleb Adwan, Department of Biology and Biotechnology, An-Najah N. University, P.O. Box 7, Nablus, Palestine 134 Synergistic Effects of Plant Extracts and Antibiotics on Staphylococcus aureus Strains Isolated from Clinical Specimens Ghaleb Adwan and Mohammad Mhanna 1 2 Department of Biology and Biotechnology, An-Najah N. University, 1 P.O. Box 7, Nablus, Palestine Faculty of Graduate Studies, Department of Environmental Sciences, 2 An-Najah N. University, P.O. Box 7, Nablus, Palestine Abstract: 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 of different mechanisms (protein synthesis inhibition: oxytetracycline HCl and gentamicin sulfate; cell wall synthesis inhibition: penicillin G and cephalexin; folic acid synthesis inhibition: Sulfadimethoxine as sodium; and nucleic acid synthesis inhibition: enrofloxacin) using both well-diffusion and microdilution method. This study was conducted against five S. aureus isolates; one is Methicillin-resistant Staphylococcus aureus (MRSA) and 4 Methicillin-sensitive Staphylococcus aureus (MSSA). 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 against the five strains of S. aureus, while using microdilution method showed synergistic effects between combination of antibiotics and plant extracts 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 against test antibiotics including these plants showed weak antibacterial activity by well diffusion method. Also our results showed that synergism effect between antimicrobial agent and plant extract was occurred in both sensitive and resistant strains but the magnitude of minimum fold inhibition in resistant strains especially MRSA strain was higher than the sensitive strains. Key words: Plant extracts Synergistic effects Antimicrobial agents Microdilution method Well diffusion method INTRODUCTION Few studies have found that the efficacy of The wide use of antibiotics in the treatment of with crude plant extracts against different pathogens bacterial infections has led to the emergence and spread including S. aureus, P. aeruginosa, E. coli, Extended of resistant strains. Methicillin-resistant Staphylococcus Spectrum -lactamases-producing multidrug-resistant aureus (MRSA) is a major cause of nosocomial infections. E. coli and vancomycin-resistant enterococci MRSA infections are very difficult to cure because MRSA (Enterococus fecalis) [6-18]. Some Palestinian plants strains are resistance against almost all clinically available exhibit significant potency against human bacterial antibiotics. For most MRSA strains, glycopeptide-type [19-21]. But plant extracts as antimicrobials are rarely used drugs such as vancomycin are the only effective as systemic antibiotics at present, this may be due to their antimicrobial agents [1]. However, vancomycin-resistant low level of activity, especially against Gram-negative S. aureus (VRSA) has been reported [2-4]. Thus, it is bacteria. Here we are trying to investigate an alternative extremely important to find new antimicrobial agents or approach to the treatment of bacterial infections by able new ways that are effective for the treatment of infectious to change the phenotype of a resistant pathogen to diseases caused by drug-resistant bacteria including certain antibiotics to more susceptible pathogen to that MRSA [5]. antibiotics. This alternative approach has been evaluated antimicrobial agents can be improved by combining them