Edwardsiellosis

Table of contents

1. Introduction

2. Identification and classification

3. Hosts

4. Pathology and diagnosis

5. Virulence factors

6. Vaccines

7. Concluding remarks

8. Competing interests

9. Authors’ contributions

10. Acknowledgements

11. References

1. Introduction

Edwardsiellosis, caused by Edwardsiella tarda, has been reported worldwide in economically important fish spe- cies, including Japanese eel (Anguilla japonica), red sea bream (Pagrus major), yellowtail (Seriola quinqueradiata), channel catfish (Ictalurus punctatus), and turbot (Scophthalmus maximus) [1-4]. This infection also leads to serious economic losses in the aquaculture of olive flounder (Japanese flounder; Paralichthys olivaceus), the most important fish species in South Korean aquaculture,

* Correspondence: jungts@gnu.ac.kr

1Aquatic Biotechnology Center, College of Veterinary Medicine, Gyeongsang National University, Jinju 660-701, South Korea

Full list of author information is available at the end of the article

with production valued at 489.7 billion Korean Won (40 922 MT), which corresponds to 56.5% of total fisheries production in 2010 [5-7].

Recent studies on vaccine development have applied a variety of antigen-preparation methods; however, com- mercial vaccines are not yet available. In addition, nu- merous studies have reported on virulence factors of E. tarda and immune responses of hosts. In the present study, the pathogenicities of E. tarda in fish that can be exploited to elicit effective protection strategies against edwardsiellosis will be discussed.

2. Identification and classification

The genus Edwardsiella is composed of three species, E. tarda, E. ictaluri, and E. hoshinae [8-10]. Fish are usually infected with E. tarda or E. ictaluri, whereas E. hoshinae infection is usually reported in reptiles and birds [11]. Panangala et al. [12] suggested that bio- chemical tests can differentiate E. tarda from E. icta- luri among bacteria isolated from freshwater fish based on the positive reaction of E. tarda in tests of indole production, methyl red reduction and hydrogen sulfide generation. In protein profiling of bacterial isolates using sodium dodecyl sulfate-polyacrylamide gel elec- trophoresis (SDS-PAGE) and Western blotting, the authors also demonstrated that E. ictaluri is more homogenously distributed than E. tarda.

E. tarda was originally isolated from cultured Japanese eel (Anguilla japonica) in Japan in 1962 [1]. Subsequent findings for the bacterium were reported from snakes in Japan [13] and from human feces in the USA; the bac- terium was designated E. tarda by Ewing et al. [8]. Al- though there was a move to change the epithet tarda to anguillimortiferum since it had been initially reported as Paracolobactrum anguillimortiferum [14], the bacterium is commonly named E. tarda because P. anguillimorti- ferum was not registered and the original culture was lost [6,15].

E. tarda is a Gram-negative, short, rod–shaped, fac- ultative anaerobic bacterium that measures about 2–3 μm in length and 1 μm in diameter [11]. It is usually motile, but isolates from red sea bream and yellowtail are non-motile [16]. This bacterium can sur- vive at 0–4% sodium chloride, pH 4.0–10.0, and 14– 45°C [17]. The biochemical characteristics of E. tarda are catalase positive, cytochrome oxidase negative, pro- duction of indole and hydrogen sulfide, fermentation of glucose, and reduction of nitrate to nitrite [11]. However, several variations of biochemical tests have been found for ornithine decarboxylase, citrate utilization, hydrogen sulfide production, and fermenta- tion of mannitol and arabinose. These discrepancies allow division into two groups: wild type and biogroup 1 [8,9,18]. The characteristics

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