Pathogenic and fecal bacteria, such as Vibrio cholerae and Escherichia coli, possibly invade via seawater. This may expose marine engineers to an intrinsic risk of infection when they carry out routine maintenance. We therefore investigated, following the voyage, the seawater taken into a ship's engine-room. As for the populations, they varied from 102.9 to 105.9 colony-forming units (cfu) ml-1. A correlation coefficient between the population and the in situ seawater temperature was 0.71, 0.30, and 0.068 for the samples taken from calls facing to the ocean (n = 6), the Inland Sea (n = 12), and the coastal area around the Pacific Ocean (n = 16), respectively. An occupational ratio of Vibrio sp. population increases when the seawater was retained for more than three months in the condensers for the air conditioner and the drain cooler. Although three strains were detected from the drain cooler, those of which had ability to make yellow-colored colonies on a selective plate at 37°C and left for 6 months. It was identified as to be Aerococcus viridans. In that species, the lobster pathogen is included, but nothing human. So far examined is pathogenic V. cholerae, which was not detected in all the samples taken from the engine-room. These results indicate that the possibility of infection of marine engineers to be quite low when they do the maintenance on board in the coastal area and the Inland Sea of Japan
