Molecular typing of bacteria Vibrio harveyi and V. alginolyticus from shrimp farming systems

Abstract

Vibriosis is a commonly encountered disease in cultured shrimps. Vibrio spp. are the natural inhabitants of marine and brackish water ecosystems, which act as opportunistic pathogens in shrimp farms and shrimp hatcheries. Since the pathogenicity of Vibrio harveyi and V. alginolyticus is highly variable, a study was conducted to collect isolates of these two species from shrimp farming systems to analyse their strain variability. The above two bacteria were isolated from shrimp-farm water, sediment, shrimp larvae and hatchery water samples and subjected to polymerase chain reaction (PCR) fingerprinting using insertion sequence (IS) targeted primers. The IS primers were able to differentiate the intraspecies variability existing in both V. alginolyticus and V. harveyi strains efficiently. Twenty strains of V. alginolyticus tested differentiated into nine fingerprint patterns and 14 strains of V. harveyi also differentiated into 8 fingerprint groups. Dendrogram analysis of the two species tested was not able to associate the virulence factors studied, viz. production of amylase, gelatinase and lipase genetically. However, it has been found that all the amylase lacking V. alginolyticus strains except one belonged to a single genogroup. Dendrogram analysis confirmed the source independent genetic variability present within the same species of Vibrio tested.