Variation of extracellular proteases produced by Vibrio vulnificus clinical isolates: Genetic diversity of the metalloprotease gene (vvp), and serine protease secretion by vvp-negative strains

Vibrio vulnificus is a causative agent of septicemia or wound infection in human and eel; however, the genetic variation between human and eel isolates has been reported. In the present study, the difference in the vvp gene encoding a tissue-damaging metalloprotease was investigated. The gene of strain E86 from a diseased eel (type B vvp) was 95.2% identical with that of strain L-180 from human blood (type A vvp). PCR using oligonucleotide primers designed to differentiate two types of the gene showed that eel avirulent strains (9 isolates) commonly carry type A vvp, whereas eel virulent strains (18 isolates) revealed significant genetic variation. The vvp genes from 12 strains including strain E86 were placed on type B while those from 3 strains were on type A. Other strains were found to be vvp-negative, but PAGE and amino acid sequencing analysis showed that they secreted a serine protease (VVA0302) instead of the metalloprotease. This protease is an orthologue of a toxic protease from Vibrio parahaemolyticus, a human pathogen causing wound infection as well as gastroenteritis. These findings suggest that, in addition to metalloprotease, the extracellular serine protease may contribute to pathogenicity of V. vulnificus.