Antibacterial Activity of Gracilaria verrucosa Extract Against Fish Pathogenic Bacteria Pseudomonas fluorescens

Abstract

The fisheries sector is essential to the economy of the coastal communities in South Java Island. The primary indicator in fish farming is the health of the fish. As the fisheries business develops, the risk of fish mortality due to bacterial infections increases. One of the infecting bacteria is Pseudomonas fluorescens, which causes Pseudomoniasis. G. verrucosa seaweed is a product of fish ponds that contains bioactive compounds, and it is necessary to conduct antibacterial tests. The aim of this research is to determine the antibacterial activity and the optimal concentration of G. verrucosa seaweed extract in inhibiting the growth of P. fluorescens bacteria. The research stages include extraction, bacterial re-culturing, extract dilution, and antibacterial activity testing using the well diffusion method. Antibacterial activity was tested at extract concentrations of 100 mg/mL, 150 mg/mL, 200 mg/mL, and 250 mg/mL, resulting in inhibition zone diameters of 4.02 ± 1.26 mm, 4.18 ± 2.57 mm, 5.6 ± 3.59 mm, and 9.97 ± 5.84 mm, respectively. Data were analyzed descriptively and statistically using SPSS 26 to examine significant differences between the produced inhibition zone diameters. Based on the analysis results, it can be concluded that all four extract concentrations have antibacterial activity, and the optimum concentration is 250 mg/mL. This research demonstrates the ability of G. verrucosa seaweed to inhibit the growth of the pathogenic bacterium P. fluorescens, which is expected to serve as a basis for the development of natural antibacterial products in the field of fisheries.