Abstract
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 30ËšC. 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 byCalotropis gigantean and Costus speciosus (7.3 mm). Plant extracts were reported for the presence of alkanes, alkenes, aromatics, primary and secondary amines etc, byFourier 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. Key words: V. harveyi, extraction of N-acyl homoserine lactones (AHL), analysis by Liquid chromatography and mass spectrometry (LC-MS), terrestrial plants, antagonism,Fourier transform infra red spectroscopy.
Highlights
Aquaculture continues to be the fastest-growing animal food producing sector
The samples were pre-enriched in alkaline peptone water (APW) and serially diluted with normal saline (0.85 % NaCl, w/v) and 0.1 ml of enriched inoculums was surface spread on Thiosulphate citrate bile salts sucrose agar medium (TCBS), Seawater complex agar (SWC) and V. harveyi selective agar medium (VHSA) separately
100 Vibrio strains were isolated from low saline water and 26 of them were identified as V. harveyi, following various biochemical tests and by the presence of vhh gene
Summary
Aquaculture continues to be the fastest-growing animal food producing sector. In shrimp grow-out practices, higher stocking densities always cause diseases by aquatic pathogenic bacteria, viruses and environmental contaminants3276 Afr. Aquaculture continues to be the fastest-growing animal food producing sector. In shrimp grow-out practices, higher stocking densities always cause diseases by aquatic pathogenic bacteria, viruses and environmental contaminants. (Darshanee et al, 2011). Vibriosis is one of the major disease problems in aquaculture (Christopher et al, 2010). Vibrio harveyi is causing bio-luminescence in both the shrimp larviculture and grow-out practices (Srinivasan and Ramasamy, 2009) that cause complete mortality especially among the postlarvae of shrimp hatcheries (Kannapiran et al, 2009). V. harveyi produce many virulence factors such as protease, phospholipase, haemolysin, cysteine protease, metallo protease, serine protease and chitinase (Defoirdt et al, 2010)
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