Seasonal recovery of Edwardsiella piscicida from wild European eels and natural waters: Isolation methods, virulence and reservoirs

Abstract

A total of 127 wild eels caught in the L'Albufera Lake (Spain) and 24 samples of lagoon freshwater were analysed for 1-year period. Edwardsiella strains were isolated from liver/kidney on TSA-1 plates in 31.9% of total diseased specimens, and the edwardsiellosis prevalence in the fishery was of 11.8%. The use of double-strength Salmonella-Shigella (DSSS) broth and SS agar yielded Edwardsiella isolation from intestine in 100% of those edwardsiellosis-diseased eels, but also in 40.4% of other sick fish with vibriosis or aeromonosis and in 28.8% of healthy eels, as well as from freshwater in 8.3% of samples. Pure cultures were isolated on SS agar from the former, but motile Aeromonas, Plesiomonas shigelloides and Hafnia alvei were recovered along with Edwardsiella in the other samples. Edwardsiella isolates identification at species level revealed that E. piscicida was distributed between wild eels and freshwater but E. tarda only did in freshwater. All E. piscicida strains were virulent for eels (LD < 1.0 × 10 CFU/fish) but that of E. tarda was not. This is the first report of E. piscicida in wild eel intestines and natural freshwater, highlighting its role as potential reservoirs for the bacterium. A seasonal recovery was found for E. piscicida at water temperature above 20°C.

Monitoring the Starvation–Survival Response of Edwardsiella piscicida and E. tarda in Freshwater Microcosms, at Various Temperatures

“…Three Edwardsiella strains were used in the study: E. piscicida V12.1 isolated from kidney of diseased European eel [ 19 ], E. piscicida V57.2 isolated from intestine of healthy European eel [ 10 ] and E. tarda V43.2 isolated from lagoon freshwater [ 10 ]. These strains were previously identified by biochemical traits as well as 16S rRNA sequencing [ 10 ]. Unless otherwise stated, cells were grown in Luria Bertani (LB, Pronadisa, Alcobendas, Spain) broth and agar (LBA, Pronadisa) at 28 °C for 24 h.…”

“…The search for Edwardsiella reservoirs in wild aquatic vertebrates and natural surface waters has primarily been a public health issue [ 6 , 7 ] because E. tarda cause water- and foodborne infection in humans [ 2 ]. To date, the Edwardsiella have been effectively isolated from diseased aquatic vertebrates [ 8 , 9 , 10 ] and, to a lesser extent, from “healthy carriers” [ 6 , 10 , 11 ]. In addition, E. tarda have been isolated from natural surface freshwater on a few occasions [ 8 , 10 ].…”

“…To date, the Edwardsiella have been effectively isolated from diseased aquatic vertebrates [ 8 , 9 , 10 ] and, to a lesser extent, from “healthy carriers” [ 6 , 10 , 11 ]. In addition, E. tarda have been isolated from natural surface freshwater on a few occasions [ 8 , 10 ]. Regarding E. piscicida , the only data on its presence in nature describe its isolation from wild eels ( Anguilla anguilla ), but scarcely from lagoon freshwater, with all samples being collected at the L’Albufera Lake (Mediterranean Spain) over a 12-year period [ 10 , 12 ].…”

“…In addition, E. tarda have been isolated from natural surface freshwater on a few occasions [ 8 , 10 ]. Regarding E. piscicida , the only data on its presence in nature describe its isolation from wild eels ( Anguilla anguilla ), but scarcely from lagoon freshwater, with all samples being collected at the L’Albufera Lake (Mediterranean Spain) over a 12-year period [ 10 , 12 ]. Since Edwardsiellosis disease arises within populations in warm seasons [ 10 , 13 , 14 ], its continuous incidence in the fishery over a long time period is an intriguing problem [ 10 , 12 ].…”

Genome-Wide Identification of Fitness Factors in Seawater for Edwardsiella piscicida

“…Edwardsiella piscicida (formerly named E. tarda) (6,7) is an important etiological agent of edwardsiellosis in marine fish, especially in farmed fish during the summerautumn seasonal changes, resulting in enormous losses to aquaculture industries worldwide (8). E. piscicida is a member of the Enterobacteriaceae and has a broad host range, such as turbot, flounder, and ϳ20 other piscine species (9).…”