Abstract

There has been augmented curiosity in the application of herbal products against diseases causing marine pathogenic bacteria in aquaculture system. This paper describes antagonism of different types of garlic extract on the growth of Vibrio harveyithat produces luciferase, virulence and bio-luminescence. Aqueous filtered garlic extract (AFGE) showed zone of inhibition (12.33 ± 0.50 mm) against V. harveyi. But aqueous unfiltered garlic extract (AUGE) showed less zone of inhibition. V. harveyi treated with AFGE showed reduced growth varying from 0.32 to 0.26 OD as compared to the control. UV treated AFGE showed 9.0 ± 0.50 mm zone of inhibition against V. harveyi. But during heat treatment at 100 and 121°C, the extracts lost their activity. Most of the virulence factors exhibited by V. harveyi were found to be reduced by AFGE treatment. Crude bacteriocin values changed from 0.10 to 0.24 OD as compared to the control (1.60 OD) for the 5 days. The cellular luciferase level was reduced to 86, 98, 79 and 94 counts per second (CPS, that is, photons/second) and the different CPS values are 23, 06, 12, 12 compared to the control. AFGE treatment also reduced bio-luminescence counts (30, 29, 35 and 30 CPS) with the differences being 14, 07, 09, 06. Challenge experiment proved that AFGE used in treating post larvae of Penaeus monodon showed less cumulative percentage mortality. In the control, maximum mortality of 2 - 42% occurred for 30 days. But in the AFGE treatment, mortality varied from 0.5 to 5.5%. Therefore, garlic extract may be a source of herbal product for controlling bacterial diseases in aquaculture.

Key words: Garlic extracts, Vibrio harveyi, virulence factors, bio-luminescence, luciferase, P. monodon larviculture.