Vibrio vulnificus is a halophilic estuarine bacterium that causes fatal septicemia and necrotizing wound infections in humans. Virulent V. vulnificus isolates produce a catechol siderophore called vulnibactin, made up of one residue of 2, 3-dihydroxybenzoic acid (2, 3-DHBA) and two residues of salicylic acid (SA). Vulnibactin biosynthetic genes (VV2_0828 to VV2_0844) are clustered at one locus of chromosome 2, expression of which is significantly up-regulated in vivo. In the present study, we decipher the biosynthetic network of vulnibactin, focusing specifically on genes around SA and 2, 3-DHBA biosynthetic steps. Deletion mutant of isochorismate pyruvate lyase (VV2_0839) or 2,3-dihydroxybenzoate-2,3-dehydrogenase (VV2_0834) showed retarded growth under iron-limited conditions though the latter showed more significant growth defect than the former, suggesting a dominant role of 2, 3-DHBA in the vulnibactin biosynthesis. A double deletion mutant of VV2_0839 and VV2_0834 manifested additional growth defect under iron limitation. Though the growth defect of respective single deletion mutants could be restored by exogenous SA or 2, 3-DHBA, only 2, 3-DHBA could rescue the double mutant when supplied alone. However, double mutant could be rescued with SA only when hydrogen peroxide was supplied exogenously, suggesting a chemical conversion of SA to 2, 3-DHBA. Assembly of two SA and one 2, 3-DHBA into vulnibactin was mediated by two AMP ligase genes (VV2_0836 and VV2_0840). VV2_0836 deletion mutant showed more significant growth defect under iron limitation, suggesting its dominant function. In conclusion, using molecular genetic analytical tools, we confirm that vulnibactin is assembled of both 2, 3-DHBA and SA. However, conversion of SA to 2, 3-DHBA in presence of hydrogen peroxide and growth profile of AMP ligase mutants suggest a plausible existence of yet unidentified alternative siderophore that may be composed solely of 2, 3-DHBA.

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Molecular characterization of vulnibactin biosynthesis in Vibrio vulnificus indicates the existence of an alternative siderophore

Vibrio vulnificus is an opportunistic human pathogen that is highly lethal and is responsible for the overwhelming majority of reported seafood-related deaths in the United States ([30][1], [117][2]). This bacterium is a part of the natural flora of coastal marine environments worldwide and has been

Vibrio vulnificus: Disease and Pathogenesis

The epidemiology of 690 Vibrio infections reported in Florida during 1981-1993 is described. Most infections resulted in one of three clinical syndromes : gastroenteritis (51%), wound infections (24%), or primary septicemia (17%). Case-fatality rates were 1% for gastroenteritis, 5% for wound infections, and 44% for primary septicemia. While gastroenteritis had little seasonal variation, 91% of primary septicemias and 86% of wound infections occurred from April through October, mostly due to the seasonality of Vibrio vulnificus and Vibrio parahaemolyticus infections. Infected wounds were largely a result of occupational activities around seawater. Some 68% of gastroenteritis cases and 83% of the primary septicemias were associated with raw oyster consumption. Preexisting liver disease was present in 48% of patients with primary septicemia and was associated with a fatal outcome in both wound infections (relative risk [RR], 28.3 ; 95% confidence interval [CI], 6.3-127.5 ; P <.0001) and primary septicemia (RR, 1.9 ; 95% C1, 1.2-3.1 ; P <.01).

The epidemiology of Vibrio infections in Florida, 1981-1993

Epidemiology and pathogenesis of Vibrio vulnificus.

Vibrio vulnificus is an estuarine bacterium responsible for 95% of all seafood-related deaths in the United States. The bacterium occurs naturally in molluscan shellfish, and ingestion of raw oysters is typically the source of human infection. V. vulnificus is also known to enter a viable but nonculturable (VBNC) state, wherein the cells are no longer culturable on routine plating media but can be shown to remain viable. Whether or not this human pathogen remains virulent when entering the VBNC state has not been definitively demonstrated. In this study, the VBNC state was induced through a temperature downshift to 5 degrees C, with cells becoming nonculturable ( 10(5) cells in the VBNC state were present in the inoculum. Culturable cells of V. vulnificus, with identification confirmed through PCR, were recovered from the blood and peritoneal cavities of mice which had died from injections of cells present in the VBNC state for at least 3 days. Thus, our data suggest that cells of V. vulnificus remain virulent, at least for some time, when present in the VBNC state and are capable of causing fatal infections following in vivo resuscitation. Our studies also indicate, however, that virulence decreases significantly as cells enter the VBNC state, which may account, at least to some extent, for the decrease in infections caused by this bacterium during winter months.

In vivo resuscitation, and virulence towards mice, of viable but nonculturable cells of Vibrio vulnificus.

16 Vibrio vulnificus strains isolated from clinical and environmental sources were studied. 6 strains (4 clinical and 2 environmental) were virulent in both an infant mouse intragastric inoculation model and an iron-loaded adult mouse model; there was a close correlation between results in the two models. Virulence was not associated with increased in vitro production of extracellular cytotoxin-hemolysin or protease. There was some correlation between virulence and the ability of a strain to grow in an iron-limited medium, with a significant association observed between virulence and utilization of transferrin as an iron source. Our results suggest that the ability to make use of available host iron is an important determinant for pathogenicity of V. vulnificus.

Virulence of Vibrio vulnificus: association with utilization of transferrin-bound iron, and lack of correlation with levels of cytotoxin or protease production

Patrick K. Wood

Papers

Virulence of Vibrio vulnificus: association with utilization of transferrin-bound iron, and lack of correlation with levels of cytotoxin or protease production