Evaluation of the antibacterial activity of selected herbal extracts against Aeromonas schubertii causing visceral white spot disease in Snakehead fish (Channa sp.)

Abstract

This study aims to evaluate the antibacterial activity of five herbal extracts, Terminalia catappa (LB), Piper betle (TK), Psidium guajava (OI), Nelumbo nucifera (LS), and Andrographis paniculata (XTL), against Aeromonas schubertii CL238, a pathogenic agent responsible for visceral white spot disease in Snakehead fish (Channa sp.). The agar well diffusion method was employed to assess antimicrobial activity, as well as determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). All five extracts exhibited inhibitory effects against the growth of A. schubertii CL238. Specifically, the LB, TK, and OI extracts demonstrated MIC/ MBC values of 6.25/12.5 mg/ml, while LS and XTL presented MIC/MBC values of 12.5/25 mg/ml. Based on their demonstrated antibacterial efficacy, the TK and OI extracts were selected to assess safety on Snakehead fingerling fish at doses of 1xMBC and 5xMBC. After a two week observation period, the 1xMBC dose caused no mortality (100% survival) for both extracts, whereas the 5xMBC dose resulted in survival rates of 85±5% (TK) and 35±5% (OI). Furthermore, the median lethal dose (LD₅₀) of A. schubertii CL238 on fingerling Snakehead fish (7 g/fish) was determined to be 1.7x10² CFU/ml. The results indicated that betel leaf extract showed the most favourable preliminary profile among the tested extracts.