Effects of temperature and salinity on survival of toxigenicVibrio cholerae O1 in seawater

In 1991 and 1992, the Latin American epidemic strain of Vibrio cholerae O1 was isolated from ballast water, bilge water, and sewage taken from cargo ships docked in Mobile Bay, Alabama. The findings raised questions regarding the organism's ability to survive long-term aboard ships and to withstand the exchange of ballast at sea. The effects of temperature (6, 18, and 30°C) and salinity (8, 16, and 32 ppt) on survival of V. cholerae O1 strains C6706 and C6707 and a ballast water isolate in sterile seawater were determined. The ballast water isolate, which had a D-value (number of days required to produce a 1 log₁₀ reduction in colony-forming units per milliliter) of 240 days at 18°C, 32 ppt salinity, had the longest survival time. The range of D-values was 36–240 days at 18°C, 60–120 days at 30°C, and 5–20 days at 6°C. In sterile seawater short-term survival was temperature dependent, whereas long-term survival was salinity dependent. In raw seawater, survival time of the ballast water isolate was reduced to 12–27 days, implying the existence of biological influences. As also shown in our previous work, the organism appeared to be able to survive for several months under relatively stable conditions in ballast water aboard ships; however, viability may be reduced to only a few weeks after the organism is introduced into estuarine or marine environments. Correspondence to: Susan A. McCarthy.