Fish diseases caused bypathogenic bacteria Aeromonas hydrophila is one of the obstacles for fish farming because it can cause death and loss for farmers. A. hydrophila was reported to possess resistance to several antibiotics. Therefore, there is a need to seek an alternative source of natural antimicrobials. This in vitro study aimed to examinethe effect of ethanol extracts of coffee grounds as an antimicrobial to A. hydrophila which infects carp (Cyprinus carpio). The coffee grounds were

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... cted from four traditional coffee shops in Banda Aceh, and a total of 500 g coffee grounds were extracted using 96% ethanol. Antimicrobial assay of ethanol extracts of coffee grounds was performed by the agar well diffusion method on Mueller Hinton Agar (MHA) plates. The result showed that all coffee ground extracts at concentration of 10%, 50%, and 100% were able to inhibit A. hydrophila bacteria with the highest inhibition zone of 10.96 mm posses a strong inhibition, while negative control does not indicate the existence of clear zone. The experiment confirmed the efficacy of coffee ground extracts as natural antimicrobials and suggested the possibility of utilizing them as a drugs for treatment of fish pathogenic caused by A. hydrophila.