Virulence Factors Expressed By Vibrio tubiashii, A Pathogen Of Invertebrates And Vertebrates?     Ben D.  Tall, Mahendra H.  Kothary, Sherill K.  Curtis, Rachel Delston, Marion Pereira, Nancy Flores, Steve R. Monday, and Matthew Jeletic   U.S. FDA, 200 C Street, S.W.,Washington, D.C.     Recent studies in this laboratory have revealed that Vibrio tubiashii, a known cause of bacillary necrosis in mollusks, expresses a number of virulence factors found in other pathogenic Vibrio species. Two of these factors are an extracellular cytolysin and a metalloprotease. The cytolysin has a molecular weight of 59 kDa and is inhibited by cholesterol. It lyses various types of vertebrate erythrocytes, and is cytotoxic to cells in culture, including Caco-2 cells, Chinese hamster ovarian cells, and Atlantic menhaden liver cells. The N-terminal sequence of the cytolysin displays significant homology to that of a cytolysin produced by Vibrio vulnificus. Preliminary results obtained from degenerative PCR analysis using primers based on the N-terminal sequence yielded a theoretical 60 bp amplicon. In addition, a theoretical 1456 bp amplicon was obtained using primers based on the cytolysin gene of V. vulnificus that included the conserved sequence of the ribosome-binding site. The metalloprotease of V. tubiashii displays biological properties that are indistinguishable from those of the metalloproteases expressed by Vibrio cholerae, V. vulnificus, and Vibrio anguillarum. Its molecular weight is 34 kDa, and the first 20 amino acids of its N-terminal sequence are identical to those of the V. cholerae metalloprotease. Oral feeding of V. tubiashii to suckling mice produced significant intestinal fluid accumulation, equal to that produced by V. cholerae. Collectively these results suggest that this molluscan pathogen produces at least two virulence factors that are related to those of other vibrios, and thus has the potential for causing diarrhea in vertebrates, including humans.