Vibrio vulnificus sepsis presenting as leg pain and lower extremity rash

Characterization of temperature-dependent hemin uptake receptors HupA and HvtA in Vibrio vulnificus

The Gram-negative pathogen Vibrio vulnificus produces several iron-sequestration systems including a hemin uptake system in response to iron limitation as a means to acquire this essential element. Strains of this organism are capable of causing serious septicemia in humans and eels, where hemin is abundant and an advantageous source of iron. Vibrio vulnificus hemin uptake systems consist of HupA, a well studied outer membrane protein, and a recently identified HvtA protein receptor. In this study, we confirmed that the expression of the hvtA gene is iron-regulated in a fur-dependent manner. When analyzed for virulence in a hemin-overloaded murine model system, the hupA gene was more important for establishing infection than the hvtA gene. Transcriptional profiling of these genes using strains of two different biotypes, biotype 1 (human pathogen) and biotype 2 (eel pathogen), showed that the expression of the two receptors was also regulated in response to temperature. The expression of hupA was highly induced in elevated temperatures in the human pathogenic strain when tested in iron-depleted conditions. Conversely, hvtA expression was induced significantly in the eel pathogenic strain at a lower temperature, a condition where the hupA locus was relatively repressed. Our results indicate that although both hupA and hvtA are involved for optimal hemin uptake in V. vulnificus, their expression is dually regulated by the environmental cues of iron concentration and temperature. Together, these data suggest that the virulence genes hupA and hvtA are tightly regulated and strictly induced during iron limitation combined with the physiological temperature of the host organism.

Vibrio vulnificus septicemia and leg ulcer

Vibrio vulnificus is a gram-negative bacteria that can cause septicemia, wound infection, or a self-limiting diarrhea. This infection typically presents as an extremely virulent infection in patients with underlying liver disease 1 to 2 days after exposure. We report a case of V vulnificus septicemia, cellulitis, and leg ulceration in a patient who had symptoms develop after exposure to brackish water (19 days before admission) or after ingestion of raw oysters (10 days before admission). The longest incubation period previously reported is 6 days. The diagnosis was made from identification of the bacteria from blood cultures. No organisms were seen or grown in culture from the skin biopsy specimen, which showed epidermal necrosis and dermal and subcutaneous neutrophilic abscess. We review 13 cases of V vulnificus septicemia and leg ulcers and their approximate incubation time.