Survival Estimation of Pathogenic Vibrio cholerae after Invasion from Ballast Water Discharged into Tokyo Bay

Marine small living things, such as planktons and bacteria, in ballast water taken into overseas vessels are transported to foreign ports by following voyages. They are spread at calls with discharged ballast water. That is threat of adaptation and growth of invasive species to new areas. An infectious risk increases when the ballast water is contaminated with pathogenic Vibrio cholerae . Exotic zebra mussels 2) and toxic dinoflagellates 3) have also been transported via ships’ ballast water and successively adapted in new areas. We have examined V. cholerae in thirty-eight of seawater samples taken on board by following a voyage in the vicinity of southeastern Japan from January to May, 2008 . So far examined, we couldn’t detect the pathogen for all of the samples. Surviving Vibrio cholerae cells, however, have been detected in the ballast water loaded on the vessels arriving to Chesapeake Bay , indicating that continuous survey of seawater in busy ports, where ballast water taken in pandemic areas is discharged, is necessary from the view point of keeping public health. Regulations adopted in 2004 by the International Convention for the Control and Management of Ships’ Ballast Water and Sediments place restrictions on acceptable microbial populations in discharged ballast water . In the convention, the number of surviving cells of Vibrio cholerae, the serum types of O1 and O139, are limited to less than one colony-forming units (CFU) 100 ml. It is important to determine the survivability of the pathogen after invasion of new habitats. In this study, therefore, a marine non-pathogenic Vibrio sp., which was isolated from a ship’s ballast water , was used to estimate the survivability of the pathogen after its invasion of Tokyo Bay. The isolate grew at 37°C and metabolized sucrose as V. cholerae does. The usefulness of a hydrogen peroxide (H2O2) solution was discussed for the pasteurization of seawater taken from busy ports in the vicinity of southwestern Japan.