Abstract

Bio-luminescence disease is caused by Vibrio harveyi, it is one of the major diseases in shrimp hatcheries and grow-out practices. V. harveyi produces virulence factors responsible for pathogenicity. The use of antibiotics as therapy for luminescence causes development of antibiotic resistance  among  the  bacterial strains.  Henceforth, it is indispensable to use bio-inhibitory agents as substitute for antibiotics from marine resources.  Hence, in this study, marine macro alga Kappaphycus alvarezii was collected, shadow-dried, pulverized and crude compounds were extracted. This algae extract at 300 µg level gave zone of inhibition (8.6 mm) against V. harveyi through “agar well diffusion assay”. The 300 mg treated with V. harveyi in LB broth and virulence factors produced were monitored for five days. Results show that in the control, higher level of lipolysis, thermonuclease, proteolysis, phospholipase were observed, in the treatment, moderate level was observed. The production of luminescence was reduced to 6.0, 7.0, 9.7 and 16.0 counts per second (CPS) observed by luminometer for 4 days when compared with the control (39.6, 50.3, 59.3 and 63.6 CPS). Further, the algae extract at 200 µg/ml was tested during larviculture for 30 days. The extract gave 29.70% reduction in the cumulative percentage of mortality. This extract was characterized by FTIR, GC-MS and detected various functional compounds like alcohols, phenols, alkenes, esters and ethers, etc. These compounds may be responsible for antagonism against V. harveyi and its virulence factors. This study confirms that the crude K. alvarezii extract may be a bio-inhibitory agent to control luminescence disease causing V. harveyi.

Key words: Kappaphycus alvarezii extract, antagonism, Vibrio harveyi, virulence factors, shrimp postlarvae, mortality reduction.