DAO 86:113-122 (2009)  -  DOI: https://doi.org/10.3354/dao02119

ABSTRACT: The virulence factors of Vibrio harveyi, the causative agent of luminous vibriosis, are not completely understood. We investigated the correlations between shrimp mortality, hemolysis, the presence of a hemolysin gene (vhh), and a gene involved in the type III secretion system (the Vibrio calcium response gene vcrD). V. harveyi HY01 was isolated from a shrimp that died from vibriosis, and 36 other V. harveyi isolates were obtained from fish and shellfish in Hat Yai city, Thailand. An ocean isolate of V. harveyi BAA-1116 was also included. Thirteen isolates including V. harveyi HY01 caused shrimp death 12 h after injection. Most V. harveyi isolates in this group (designated as Group A) caused hemolysis on prawn blood agar. None of the shrimp died after injection with V. harveyi BAA-1116. Molecular analysis of all V. harveyi isolates revealed the presence of vcrD in both pathogenic and non-pathogenic strains. Although vhh was detected in all V. harveyi isolates, some isolates did not cause hemolysis, indicating that vhh gene expression might be regulated. Analysis of the V. harveyi HY01 genome revealed a V. cholerae like-hemolysin gene, hlyA (designated as hhl). Specific primers designed for hhl detected this gene in 3 additional V. harveyi isolates but the presence of this gene was not correlated with pathogenicity. Random amplified polymorphic DNA (RAPD) analysis revealed a high degree of genetic diversity in all V. harveyi isolates, and there were no correlations among the hhl-positive isolates or the pathogenic strains.

KEY WORDS: Vibrio harveyi · Type III secretion system · TTSS · vcrD · vhh · hhl · Random amplified polymorphic DNA analysis · RAPD