The role of a Vibrio vulnificus type IV pilin in pathogenesis and in persistence in oysters.

摘要

Vibrio vulnificus is a Gram negative, halophilic bacterium, which is a natural inhabitant of sub tropical and tropical marine estuarine waters. These bacteria concentrate in filter-feeding mollusks such as oysters and unlike fecal contaminants are not easily eliminated during normal shellfish processing. The specific mechanisms by which these bacteria interact with or colonize oysters are unclear. Food-borne infections, mainly by consumption of raw oysters, caused by this bacterium have a high fatality rate of about 50% in susceptible individuals. This bacterium can also cause severe wound infections from handling fish or shellfish. 20--30% of which are fatal.; Bacterial adherence to biotic and abiotic surfaces is mediated by several mechanisms including pill, flagella, surface polysaccharide capsules and non-fimbrial adhesions. This study verifies that one of the pilins of V. vulnificus , PilA, of the type IV class of pili, contributes to virulence in a mouse model, adherence to human epithelial cells, and biofilm formation on abiotic surfaces. Loss of PilA also resulted in a decrease in the ability of this bacterium to persist in oysters. A strain with a mutation in the type IV prepilin peptidase, PilD, which is defective in expression of all surface pili and secretion of exoenzymes that are exported by the type II secretion pathway was also less persistent in oysters as compared to the wild type strain. If these factors prove to be responsible for the bacterium's ability to colonize oyster tissue, they may present a unique and specific target(s) for compounds designed to interfere with this attachment, leading to depuration methods that could potentially reduce or eliminate the bacteria from oysters.; Examination of the Y. vulnificus pilA sequences from several clinical and non clinical isolates demonstrates that these pilins cluster into a limited number of groups within which the amino acid sequences are almost identical, although the sequences between groups are considerably variable. Preliminary phylogenetic analysis also suggests that the sequence diversity in pilA is similar to that of drE, an Escherichia coli fimbrial adhesin that is both the structural and adhesin gene, raising the possibility that pilA may be evolving in a similar fashion.