Molecular Identification of <i>Vibrio alginolyticus</i> Causing Vibriosis in Shrimp and Its Herbal Remedy

Abstract

<i>Penaeus monodon</i> is highly susceptible to vibriosis disease. Aims of the study were to identify the pathogen causing vibriosis in <i>P. monodon</i> through molecular techniques and develop a biocontrol method of the disease by application of herbal extracts. Shrimp samples were collected aseptically from the infected farm and the bacteria were isolated from the infected region of those samples. Based on phenotypic identification, several isolates were identified as <i>Vibrio</i> sp. 16S rRNA gene sequences of the selected isolates exhibited 100% homology with <i>V. alginolyticus</i> strain ATCC 17749. An <i>in vivo</i> infection challenge test was performed by immersion method with <i>V. alginolyticus</i> where these isolates caused high mortality in juvenile shrimp with prominent symptoms of hepatopancreatic necrosis. Antibiogram profile of the isolates was determined against eleven commercial antibiotic discs whereas the isolates were found resistant to multiple antibiotics. A total of twenty-one herbal extracts were screened where <i>Emblica officinalis, Allium sativum</i>, and <i>Syzygium aromaticum</i> strongly inhibited the growth of <i>V. alginolyticus</i> in <i>in vitro</i> conditions. In <i>in vivo</i> conditions, the ethyl acetate extracts of <i>E. officinalis</i> and <i>A. sativum</i> successfully controlled the vibriosis disease in shrimp at a dose of 10 mg/g feed. This is the first report on molecular identification and biocontrol of <i>V. alginolyticus</i> in shrimp in Bangladesh.