Electron Microscopic Study of In Vitro Vibrio vulnificus Infection to Tissue Culture Cells and Peripheral Blood Cells

Vibrio vulnificus is the most pathogenic species among the genus Vibrio, and such a fatal V. vulnificus infection case occurred in Niigata in 2003. In this study, we investigated the in vitro characteristics of V. vulnificus infection to tissue culture cells (HEp-2, HeLa, and HCT-8) and human peripheral blood cells by scanning and transmission electron microscopy. V. vulnificus damaged those cells, especially HeLa cells. Moreover, V. vulnificus adhered to cells possessed unique pearl-like structure, unlike V. cholerae O1 or O139 and V. parahaemolyticus. When human peripheral blood cells were infected with V. vulnificus, leukocytes and platelets were markedly adhered with V. vulnificus, and platelet was most seriously damaged. Separation of the outer and inner nuclear membranes was observed in some blood cells such as leukocytes. Pilus-mediated V. vulnificus adherence to blood cells was also observed. Invasion (or uptake) of V. vulnificus into blood cells was not obvious, in contrast to methicillin-resistant Staphylococcus aureus. The data suggest that V. vulnificus may use unique appendages for infection, and may damage blood cells such as platelets and leukocytes by producing toxins rather than invading cells, and prevent phagocytosis by bacterium-engulfing cells by toxins.