Isolation and identification of fish pathogenEdwardsiella tardafrom mariculture in China

Abstract

The causative agent was isolated from diseased turbots (Scophthalmus maximus) stricken by a highmortality outbreak of bacterial septicaemia occurring in a mariculture farm in Yantai, a northern coastal city of China. Seven pure isolates, namely EH-15, EH-103, EH-107, EH-202, EH-203, EH-305 and EH-306, belonged to Edwardsiella tarda. The phenotypic features of the cultures were analysed extensively. Three of the isolates showed high 16S rDNA sequence similarities with E. tarda sequence (GenBank accession no. EF467289). However, unlike the E. tarda ATCC 15947, all the isolates, except EH-15, contained a novel large plasmid sized about 23.7 kb. Furthermore, pathogenicity of the isolates was addressed by experimental challenges with ¢sh models. The isolates exhibited strong virulence to swordtail ¢sh with LD 50 ranging between 3.8 Â 10 3 and 3.8 Â 10 5 CFU g À 1, and EH-202 displaying the lowest LD 50 value among them. Antibiotic susceptibilities of E. tarda isolates were assayed. Compared with E. tarda ATCC 15947, the isolates displayed strong resistance to chloramphenicol, and the probable dominant chloramphenicol resistance determinant was cat III. Depicting the main biological properties of turbot-borne E. tarda strains in China, the study provided useful information for further unveiling their pathogenic mechanisms.

Isolated faecal bacterial communities found for Weddell seals, Leptonychotes weddellii, at White Island, McMurdo Sound, Antarctica

“…Leotta et al (2009) identified the bacterium in Antarctic sea birds and penguins, and Weddell seals. Although the bacterium has been associated with diseased fish (Xiao et al 2008), E. tarda is considered a common bacterium of Antarctic wildlife that probably does not cause any clinical signs of disease (Leotta et al 2009). Several of the bacterial clones' closest matches have been identified from the gastrointestinal tracts of other seal species.…”

QseBC controls flagellar motility, fimbrial hemagglutination and intracellular virulence in fish pathogen Edwardsiella tarda

“…tarda isolates were pathogenic to freshwater or marine fish [23,30]. Intramuscularly infections caused by E. tarda exhibited typical symptoms of edwardsiellosis including haemorrhagic necrotic lesions in skin and muscle with suppurative abscesses, suggesting that this pathogen can invade cells to spread systemically and cause tissue damage in vivo [30].…”

Edwardsiella tarda T6SS component evpP is regulated by esrB and iron, and plays essential roles in the invasion of fish

“…The E. tarda strains used in this study (Table 1) were isolated and identified as previously described [23]. Briefly, the isolates were grown on Salmonella-Shigella agar (SS, Difco) at 28 C. Small colonies with black centers were picked up and re-streaked onto SS agar to ensure purity.…”