Extraction and detection of quorum sensing N- acyl homoserine lactones from shrimp pathogen Vibrio harveyi and antagonistic effect of terrestrial plants against its growth

Vibrio harveyi strains were isolated from the water samples of low salinity. Isolates were confirmed by both the presence of vhh gene using polymerase chain reaction and bio-chemical tests. V. harveyi was grown in LB medium and its spent culture was treated with ethyl acetate. The organic layer was pooled and dried by Roto Vapour with vacuum at 30 ̊C. The dried residues were dissolved with 50 % acetonitrile and water. The presence of N-acyl homoserine lactones (AHL) compounds from the residues of crude extract and the standard “3 Oxo hexanoyl homoserine lactone” were analyzed separately using Liquid chromatography and mass spectrometry (LC-MS). Different peaks were detected and peaks corresponding to 214.4 m/z were identified as N(3-oxohexanoyl)-L-homoserine lactones in the sample. Different unknown peaks were also identified. Aqueous extracts of 47 terrestrial plants were evaluated against luminescence disease causing V. harveyi, through “Agar well diffusion assay”. Ten plant extracts showed zone of inhibition (5 to 7 mm) on V. harveyi. Extracts from Phyllanthus niruri and Cynodon dactylon showed the highest zone of inhibition (8.3 mm) against V. harveyi followed by Calotropis gigantean and Costus speciosus (7.3 mm). Plant extracts were reported for the presence of alkanes, alkenes, aromatics, primary and secondary amines etc, by Fourier transform infra red spectroscopy (FT-IR). The antagonistic activity may be due to by the presence of these functional compounds in the extracts. Therefore, terrestrial plants could be used to control aquatic bacterial pathogens, which can also be extended to control human bacterial pathogens.