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.
Highlights
The declining fish production and consumers’ growing demands for fishery products are the main factors affecting expansion of aquaculture
This paper describes antagonism of different types of garlic extract on the growth of Vibrio harveyi that produces luciferase, virulence and bioluminescence
The samples were pre-enriched in alkaline peptone water (APW) and serially diluted with normal saline (0.85 % NaCl w/v), 0.1 ml of each sample was surface spread on Thiosulphate citrate bile salt sucrose agar medium (TCBS), Seawater complex agar (SWC) and V. harveyi selective agar medium (VHSA)
Summary
The declining fish production and consumers’ growing demands for fishery products are the main factors affecting expansion of aquaculture. The association and species composition of bio-luminous bacteria in near-shore seawater, semi-intensive and brackish water fed shrimp grow-out systems of Tamil Nadu was reported (Abraham et al, 2008). Five species of bio-luminous bacteria, viz., Photobacterium leiognathi, Vibrio fischeri, V. harveyi, Vibrio orientalis and Vibrio splendidiis biotype 1 were encountered in seawater fed shrimp grow-out ponds. Mass mortality of tiger shrimp (P. monodon) larvae caused by V. harveyi showing multiple antibiotic resistances has been reported (Karunasagar et al, 1994). The quest for alternative methods to control infection caused by antibiotic-resistant Vibrios is imperative challenge for sustainable development of aquaculture. Due to the increased antibiotic resistance among bacteria, WHO recommended in exploring herbs or plants as antimicrobial agents for treating various bacterial infections (Wallace, 2004). The present study focussed on the analysis of the inhibitory activity of garlic extract against the growth of pathogenic V. harveyi in shrimp larviculture practice and interference with virulence factors
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