Antimicrobial activity screening of Lyngbya majuscula crude methanolic extract against selected aquaculture pathogens

Lyngbya majuscula crude methanolic extract (LMCME) was screened for antimicrobial properties in vitro. The Gram-negative Vibrio harveyi and Aeromonas hydrophila and the Gram-positive Staphylococcus aureus and Micrococcus luteus were used as reference test bacteria. The filamentous Lagenidium sp. was used as test fungus. LMCME showed a poor or weak antibacterial activity against the bacterial isolates. The activity against V. harveyi was observed at 1,000 mg/mL-1 while that against A. hydrophila was at 500 and 1,000 mg/mL-1 concentrations. These activities, however, were significantly lower (p-1 concentration and was comparable (p>0.05) with the positive control (malachite green). The minimum inhibitory concentration (MIC) of LMCME against Lagenidium sp. was at 50 mg/mL-1, and the minimum fungicidal (lethal) concentration (MFC) at 100 mg/mL-1. Phytochemical screening revealed the presence of alkaloids to which its antifungal activity may be attributed. Brine shrimp assay against the larvae of Artemia salina L each showed that the LMCME was not toxic even at the highest concentration (1,000 mg/mL-1). By and large, L. majuscula can be a potential source of secondary metabolites that can be used for the control and treatment of larval mycosis in the aquaculture industry