Synergistic Antibacterial Effect of Extracts in Combination with Antibiotics against Fish Pathogenic Bacteria.

The aquaculture industry faces significant challenges due to bacterial infections caused by , , and . The extensive use of traditional antibiotics, has resulted in widespread antibiotic resistance. This study aimed to investigate the antibacterial potential of the brown seaweed , particularly its synergistic effects with antibiotics against these fish pathogenic bacteria. were processed to obtain methanolic extracts and fractionated using different polar solvents. The antibacterial activities of these extracts and fractions were assessed through disc diffusion and minimum inhibitory concentration (MIC) assays. The study further evaluated the antibiotic susceptibility of the bacterial strains and the synergistic effects of the extracts combined with erythromycin and oxyteteracycline using the fractional inhibitory concentration index. Results showed that the ethyl acetate (EtOAc) fraction of methanolic extract exhibited the highest antibacterial activity. The combination of the EtOAc fraction with erythromycin significantly enhanced its antibacterial efficacy against the tested strains. This synergistic effect was indicated by a notable reduction in MIC values, demonstrating the potential of to enhance the effectiveness of traditional antibiotics. The findings suggest that extracts, particularly the EtOAc fraction, could serve as a potent natural resource to counteract antibiotic resistance in aquaculture.