Study on the potential ofAaptos aaptos aqueous extract as an antibacterial agent against Vibrio harveyi in tiger shrimp (Penaeus monodon Fabricius) post larvae

Abstract

The sponge Aaptos aaptos is known to contain bioactive compounds with bactericidal properties. These compounds could be utilized in shrimp aquaculture to inhibit the growth of Vibrio harveyi, the causative agent of vibriosis. This study aimed to evaluate the antibacterial activity of an aqueous extract of Aaptos aaptos on V. harveyi isolated from diseased shrimp post larvae and identify bioactive compounds active against V. harveyi. An aqueous extract was obtained through solvent partitioning of active Aaptos aaptos extract using methanol with n-hexane and butanol. The bioactive compound was isolated from the aqueous extract through repeated column chromatography with silica gel as stationary phase and a mixture of dichloromethane and methanol as mobile phase. The antibacterial activity of the aqueous extract was tested using a 96 microwell plate with extract concentrations of 10,000, 1,000, 100, 10, 1, and 0 mg/L. An in vitro aqueous extract antibacterial activity challenge test against V. harveyi was conducted using reaction tubes with extract concentrations of 5,000, 500, 50, 5 and 0 mg/L. Antibacterial activity of isolated bioactive compounds was determined through an agar diffusion assay using paper discs with a concentration of 20 μg/disc. Results showed that the Aaptos aaptos aqueous extract displayed strong antibacterial activity with a minimum inhibitory concentration (MIC) of 10 mg/L. V. harveyi colonies treated with aqueous extract at concentrations of 500 and 5,000 mg/L had decreased drastically (5.50 × 103 and 0.83 × 102 CFU/mL respectively) 4 hours post treatment. The orange spot exhibited when sprayed with Dragendorff reagent indicated that one of the compounds successfully isolated belonged to the alkaloid group, with an Rf value of 0.2 (acetonitrile/methanol, 2:8, Q8 TLC Plate).This bioactive compound was one of those responsible for the Aaptos aaptos aqueous extract activity, with an inhibition zone of 22 ± 0.1 mm.