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The global escalation of antibiotic-resistant bacterial infections, particularly those caused by Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus (MRSA), underscores an urgent need for novel antimicrobial agents. Marine macroalgae, especially red algae from the genus Gracilaria, are increasingly recognized as promising sources of bioactive secondary metabolites with potential antibacterial properties. This study aimed to evaluate the antibacterial efficacy of Gracilaria sp. extracts and fractions against clinical isolates of S. aureus, MRSA, and S. aureus ATCC 25923 and to determine the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the most active fraction. Antibacterial activity was assessed via the agar disc diffusion method, while MIC and MBC values were determined using a microdilution assay. The extract revealed concentration-dependent inhibitory effects, with notable activity against S. aureus and MRSA observed at 30–60% concentrations and against S. aureus ATCC 25923 at 20–50%. The ethyl acetate fraction demonstrated the strongest activity, producing inhibition zones of 15.14 mm, 17.81 mm, and 22.23 mm against S. aureus, MRSA, and ATCC 25923, respectively. MIC and MBC values varied by strain, ranging between 12.5–50%. These findings suggest that Gracilaria sp. possesses potent antibacterial properties, with variable efficacy depending on the strain. It supports its potential as a natural source of anti-Staphylococcal agents to combat antibiotic resistance.

Antibacterial activity; Gracilaria sp.; MRSA; natural antimicrobial agents; red algae; Staphylococcus aureus