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Seawater used in mariculture has been suspected of being a potential source of infection. In this study, the lethal effects of low-amperage electric treatment on microorganisms were examined in natural seawater and in seawater inoculated with Vibrio parahaemolyticus. In both cases, bacteria including V. parahaemolyticus in seawater were completely eliminated in 100 ms by a 0.5-A, 12-V direct current. Electron microscopic investigation of the electrically treated bacteria revealed substantial structural damage at the cellular level. In conclusion, our results indicate that low-amperage electric treatment is effective for rapid inactivation of microorganisms in seawater.The prevalence and distribution of bacteria such as Vibrio species in aquatic environments are of great public health concern because Vibrio spp. are pathogenic for both humans and animals (18). Recent outbreaks of Vibrio parahaemolyticus in the United States have been associated with eating behavior such as the consumption of raw or undercooked seafood, including fish and shellfish (1, 4, 9). Hence, seawater used for the cultivation and washing of fish and shellfish is another potential source of infection. However, conventional techniques of water sterilization are typically unsuitable for seawater. Antibiotics, for example, have come to be commonly used to prevent diseases due to seafood in fishery and culture, but chemical disinfectants may be toxic, deteriorate with an abnormal smell, and cause increased resistance to antibiotics (8). Heat sterilization is not suitable for large-scale treatment and culturing of fish (12). Ozone and UV light are efficient and produce harmless derivatives but are more costly (3,5,19). Recently, the use of pulsed electric fields, which are nonthermal and nonchemical, has been researched for sterilization of water (13,16,21,22). However, the industrial plant required for such treatment represents a major investment for manufacturers because of the limited application of high-voltage electric fields. We also have studied an electric sterilization method for seawater that is based on low-amperage direct-current transfer between bacterial cells and electrodes rather than on the generation of toxic substrates such as H 2 O 2 (10). In contrast to a pulsed electric field, the method described here uses a lowintensity electric current and is therefore potentially much simpler and cheaper to implement. In the present study, the sterilizing effect of low-amperage electric treatment for various times was studied with natural seawater and seawater inoculated with V. parahaemolyticus. Because V. parahaemolyticus is known to cause gastrointestinal illness in humans, it seemed to be suitable as our experimental model.The natural seawater used in this study was collected in the seashore of In-cheon in Korea. V. parahaemolyticus (ATCC 17802; Shirasu food-poisoning isolate) was grown in nutrient broth (Difco Laboratories, Detroit, Mich.) containing 3% (wt/ vol) NaCl at 37°C. At the end of the exponential growth phase, the cells we...

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Vibrio parahaemolyticus, the cause of gastroenteritis in humans, was inactivated by alternating low-amperage electricity. In this study, the application of alternating low-amperage electric treatment to effluent seawater was investigated for the large-scale disinfection of seawater. This method was able to overcome the problem of chlorine generation that results from treatment with continuous direct current. In conclusion, our results showed that alternating-current treatment inactivates V. parahaemolyticus in effluent seawater while minimizing the generation of chlorine and that this alternating-current treatment is therefore suitable for practical industrial applications.Vibrio parahaemolyticus is a gram-negative, halophilic bacterium that naturally inhabits marine and estuarine environments and causes three major syndromes of clinical illness: gastroenteritis (the most common syndrome), wound infections, and septicemia (11). V. parahaemolyticus has been recognized as a common cause of food-borne illness in the world (6, 16). During the past 10 years in the United States, V. parahaemolyticus has been the most common Vibrio species isolated from humans, as well as the most frequent cause of Vibrio-associated gastroenteritis (9). Recent V. parahaemolyticus outbreaks in the United States have been associated with consumption of raw or undercooked shellfish (1, 4, 5). Thus, seawater used in mariculture requires a sterile process to prevent the propagation of bacteria. As an alternative to conventional techniques of water sterilization, such as antibiotics (8), heat sterilization (10), ozone (15), UV light (3), and pulsed electric field (14), low-amperage electric treatment of bacteria in seawater was developed in a previous study (13). The method as proposed above was potentially much simpler and cheaper than any other methods for disinfection of seawater. In the present study, we evaluate the improvements and practical applications of the method for the large-scale sterilization of seawater.To apply to large-scale treatment, we employed a flow-simulating fluidic conduit made of a titanium pipe and rod, connected to a feeding pump (NP-2; Nakasa, Japan) and an electric power supply (model 525C; Metronix Corp., Tokyo, Japan) (Fig. 1). The pipe and rod were coated with a 1-m-thickness of platinum to function as direct electrodes. In passing through the space between the pipe and rod, the seawater containing V. parahaemolyticus flowed at the speed of 850 ml/min while being treated with a certain electric current. In the experiments involving static conditions, an electrolysis vessel used in previous study (13) was also employed. In this case, each experiment was applied to a stationary quantity of 5 ml of seawater.The natural seawater used in this study was collected from the seashore of In-cheon in Korea. V. parahaemolyticus ATCC 17802 (American Type Culture Collection) was grown in nutrient broth (Difco, Detroit, Mich.) containing 3% (wt/vol) NaCl at 37°C for 18 h until the end of the exponential growth phase and re...