Objective: To investigate the Quorum Sensing inhibition (QSI) potential of Limonia acidissima L. against the biofilm forming Vibrio harveyi isolated from fresh water fish. Methods: The present study evaluated the anti-quorum sensing activity of the L. acidissima methanol and ethyl acetate fruit extracts by using Chromobacterium violaceum ATCC 12472 (wild) and C. violaceum CV026 (mutant) as bio monitor strains and biofilm formation using the crystal violet assay. Vibrio sp. were isolated from fresh water cultured fishes and screened for biofilm formation property. Strong biofilm forming isolate were subjected to molecular characterization. Limonia fruit pulp was subjected to methanol and ethyl acetate extraction using cold percolation method and yield was calculated. In parallel to, determining the QSI properties of the extract, MIC, BIC, anti-biofilm properties and metabolic activity of LA-M and LA-EA against the biofilm forming V. harveyi KUMB-VA4 was determined. Results: The results of the present study demonstrated that the overall yield of methanol and ethyl acetate extract was 12.84 % and 9.3 % (w/w) respectively. Strong biofilm forming Vibrio isolate KUMB-VA4 was obtained from infected fresh water fishes and was subjected to molecular characterization. MIC of LA-M was 1510 μg/ml and LA-EA was observed to be 3000 μg/ml against the test pathogen respectively. Biofilm inhibition assay revealed a BIC of LA-M at 250 μg/ml and LA-EA at 500 μg/ml. Both the plant extracts significantly reduced the biofilm formation of V. harveyi KUMB-VA4 and the metabolic activity in a dose dependant manner. Light microscopy and scanning electron microscopy revealed that LAM and LA-EA significantly altered 68.6% and 54.5% of the biofilm architecture at BIC. The quorum sensing inhibition assay revealed that LA-M effectively reduced the violacein production of the bio monitor strains at sub-BIC (100 – 500 μg/ml) to 80% than LA-EA (43 %) in a strong dose dependent fashion. Conclusions: The present study revealed the QSI property of Limonia acidissima against the biofilm forming V. harveyi isolated from infected fish.

Keywords: L. acidissima, V. harveyi, C. violaceum, Quorum Sensing Inhibition.