ملخص
Abstract Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial infections. MRSA infections are very difficult to cure because MRSA strains are resistance against almost all clinically available antibiotics. In this study two brown algae extracts, Petalonia fascia (P. fascia) and Dictyota dichotoma (D. dichotoma) collected from Tajura western coast of Libya, were evaluated individually and in combination with Amoxicillin for antibacterial activity against five strains of MRSA (S119,S120,S122,S130,S283), using holeplate diffusion method, and by absorption measurements using spectrophotometer. The MIC and MBC of algae extracts were determined, as well as the probable mode of their antibacterial effect, was evaluated using bacterial physiological indicators, including intracellular potassium ion efflux and nucleotide leakage. Also hemolytic activity of algae extracts was assessed as an indicator of their relative cytotoxicity on human red blood cells . The following extract-antibiotic combinations were used (1:1), (1:2), (2:1). Results showed that methanolic extracts of P. fascia and D. dichotoma have a significant inhibitory action against all tested MRSA strains, with a marked advantage of P.fascia against all tested strains. Also the two algae extracts showed spectrum of bactericidal effect with a ratio MBC/MIC ≤ 4 obtained on all tested MRSA strains. Compared Amoxicillin alone, the bacterial growth of all MRSA strains was completely inhibited as absorption of each sample decreased dramatically indicating reduced bacterial growth, due to the effect of algal extract enhancing the antibacterial activity of Amoxicillin. Also the combination between tested algae extracts and Amoxicillin showed significantly induced a distinct release of nucleotide and potassium ions out of cell membrane, compared with Amoxicillin as alone, which did not showed significant results. which indicates that is a disruption in the cell membrane permeability and leakage of intracellular materials, or a rupture of the cell membrane and cell wall and exit of all the contents of cell to the outside environment. Moreover the results also showed that algae extracts possess a considerable low hemolytic activity and considered at the safe level. Therefore, our results revealed the importance of D. dichotoma and P. fascia crude extracts when associated with Amoxicillin to control MRSA strains