Growth and Survival of Edwardsiella tarda Bacteria in Environmental Water

Abstract

At present, there is no available information or other previous report on the mechanism of infection in edwardsiellosis. This study therefore, deals with the effect of temperature, pH, and NaCl concentration on the growth and survival time of E. tarda in pond water, centrifuged pond water and subterranean water at different temperatures.
In the survival time experiment, environmental water was treated with a low concentration of 10^3.3 viable cells of E. tarda except the subterranean water which was treated with 10^3.6. On the other hand 10^7.8viable E. tarda cells were introduced in the high concentration group, however, the temperature during the incubation period was maintained at 20°C, 25°C, and 30°C in both high and low concentration.
As a result, it was observed that at temperatures from 15°C to 45°C (optimum 30°C-37°C), pH of 4.0-10.0 (optimum 7.5-8.0), and at 0-4.0NaCl (optimum 0.5-1.0%), the viable cells of E. tarda could still exist. In the case of 10^3.3 inocular size, it grew in pond water and centrifuged pond water and survivd the entire 17 days or more of storage. But it died in 3 days or less in the subterranean water. In pond water, multiplication of E. tarda cells was faster than in centrifuged pond water, and it has been found that the number of cells recovered was greater in the former than in the altter water environment. In the high concentration of E. tarda cells, a greater recovery was noticed after 76 days in pond water. In all cases, survival at 20°C was equal to or better than at any other temperature.
From the results obtained, it is assumed that the bacterial cells from infected fish can survive fro a long time in environmental water, thus, the possibility of further infestation is great.