Edwardsiella ictaluri sp. nov., the Causative Agent of Enteric Septicemia of Catfish

Abstract

We characterized 13 cultures of the enteric bacterium causing enteric septicemia of catfish by studying their biochemical reactions, deoxyribonucleic hybridizations, and deoxyribonucleic acid guanine-plus-cytosine contents. We confirmed that this bacterium is a new species, which is most closely related to Edwardsiella tarda of the family Enterobacteriaceae. Five strains of the bacterium causing enteric septicemia of catfish were 80% or more related to the type strain, SECFDL GA 77-52 (= CDC 1976-78 = ATCC 33202), in 60°C deoxyribonucleic acid homology reactions. Species level relatedness among the 13 strains which we studied was demonstrated by the more than 80% relatedness in 75°C reactions. The bacterium causing enteric septicemia of catfish was most closely related to E. tarda (56 to 62%) in 60°C reactions. The guanine-plus-cytosine was 53 mol%, as determined by buoyant density centrifugation. We propose the name Edwardsiella ictaluri sp. nov. for the bacterium causing enteric septicemia of catfish.Enteric septicemia of catfish (ESC) is a newly described bacterial disease primarily of cultured channel catfish (Ictalurus punctatus) (9). The causative agent of this disease is a gram-negative, rod-shaped, 0.5-by 1.25-pm, oxidase-negative, peritrichous, fermentative bacterium that has been isolated 26 different times from the kidney tissues of moribund catfish. Biochemically, this organism is most similar to Edwardsiella tarda but differs from E. tarda in several key diagnostic characteristics (1).ESC was fist detected in 1976. Although not always consistent, the clinical signs of this disease in I. punctatus are typical of the acute bacterial septicemias caused by E. tarda, Aeromonas hydrophila, and Pseudomonas fluorescens ( 5 , 11).ESC presently constitutes an economic threat to catfish farmers in Alabama, Georgia, and Mississippi. The pathogenicity of the ESC bacterium to species of fish other than catfish has not been demonstrated, although it has been isolated from channel catfish (I. punctatus), white catfish (Ictalurus catus), and brown bullhead (Ictalurus nebulosus). In this paper we characterize, classify, and name the ESC bacterium.

The Edwardsiella ictaluri O polysaccharide biosynthesis gene cluster and the role of O polysaccharide in resistance to normal catfish serum and catfish neutrophils

“…ictaluri chromosome (53 %) ( Fig. 2) (Hawke et al, 1981). Low mol% G+C content is a common feature of bacterial polysaccharide biosynthesis clusters and is thought to reflect a heterologous origin due to lateral transfer of genetic material between species or strains (Reeves, 1993).…”

Mortality and pathology in brown bullheads Amieurus nebulosus associated with a spontaneous Edwardsiella ictaluri outbreak under tank culture conditions

“…This disease was first described in channel catfish Ictalurus punctatus by Hawke (1979), and the causative organism was later identified and characterized (Hawke et al 1981). The pathogen is a gram-negative, catalase-positive, cytochrome oxidase-negative, enteric bacterium that ferments a limited number of carbohydrates in standard bacteriological media (Waltman et al 1986).…”

Immune response of channel catfish to ipopolysaccharide and whole cell Edward-siella ictaluri vaccines

“…Studies on the immune response of fish have employed many antigens including particulate (virus), cellular (bacteria) and molecular (proteins, carbohy-MATERIALS AND METHODS drates, and haptens) substances. In a few cases, lipopolysaccharides (LPS) or endotoxins from the bacEdwardsieLla i c t a l w (Hawke et al 1981) (ATCC terial cell wall have been used to stimulate an immune 33202) was reconstituted from lyophilized pellets and response in fish (Cisar & Fryer 1974, Paterson & Fryer grown on brain-heart infusion (BHI) agar plates at 1974, Busch 1978, Ingram & Alexander 1980. Enteric 30°C.…”

“…Enteric 30°C. Cells were removed from the plates and sussepticemia of catfish (ESC), caused by EdwardsieLla pended in either 0.85 % saline or phosphate-buffered ictaluri (Hawke 1979, Hawke et al 1981) is the most saline (PBS, pH 7.2). important bacterial disease of cultured channel catfish One-year-old channel catfish (averaging 60 g each (Beleau & Francis-Floyd 1986).…”