Survival of Edwardsiella ictaluri in Pond Water and Bottom Mud

Abstract

Abstract Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish, is involved in about one-third of all disease cases in diagnostic laboratories where channel catfish (Ictalurus punctatus) is the predominant species examined. Edwardsiella ictaluri causes disease primarily when water temperatures range from 18°C to 28°C; these temperatures prevail during May and June and again in September and October in southern USA where catfish are cultured. This investigation was undertaken to confirm earlier reports that E. ictaluri does not survive in water and to determine if it could survive in bottom muds of ponds. Survival of E. ictaluri was determined in pond water at 5°C and 25°C, and in bottom mud at 5°C, 18°C, and 25°C. In mud incubated at 25°C, E. ictaluri maintained itself at densities of 106.5 cells/mL for 95 d; at 18°C the organism maintained approximately 10-fold higher densities for 40 d. However, E. ictaluri survived for less than 10 d in water at 25°C and for less than 15 d in water and mud at 5°. These data demonstrate that E. ictaluri can survive in pond bottom muds for an extended period of time; from this refuge, it may be a source of infection from spring through the fall. In view of these data, it is unlikely that E. ictaluri is a true obligate pathogen, but its survival is restricted by environmental conditions.