In aquaculture, the occurrence of bacterial resistance to synthetic antibiotics has become a serious problem. Therefore, research has been focused on finding new antimicrobial antibiotics from natural products to replace synthetic antibiotics. The aim of this study was to investigate the antimicrobial properties of mangrove plant blinding tree Excoecaria agallocha against selected fish pathogens namely Flavobacterium indicum, Chryseobacterium indologenes, Chryseobacterium gleum and Elizabethkingia meningoseptica previously named Flavobacterium meningosepticum. Mangrove leaves were obtained via extraction with 100 ml of methanol. The antimicrobial susceptibility test showed that the bacteria were resistant to Nitrofurantion, Gentamycin and Neomycin, and were sensitive to Flumequine. The minimum inhibitory concentration (MIC) of E. agallocha was 3.12 mg/ml, and minimum bactericidal concentration (MBC) was 6.25 mg/ml. Inhibition zones were significantly different (p< 0.05) depending on concentrations (100, 300 and 500 mg/ml) of the crude extraction of E. agallocha. The highest activity with LC50 of E. agallocha was 94.19 (mg/ml). Methanolic extract of E. agallocha exhibited strong antimicrobial activity against these bacteria.
Key words: Antimicrobial activities, Excoecaria agallocha, inhibition zone, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), LC50.
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