Comparative Phenotypic and Genotypic Analysis of Edwardsiella Isolates from Different Hosts and Geographic Origins, with Emphasis on Isolates Formerly Classified as E. tarda, and Evaluation of Diagnostic Methods

Abstract

spp. are responsible for significant losses in important wild and cultured fish species worldwide. Recent phylogenomic investigations have determined that bacteria historically classified as actually represent three genetically distinct yet phenotypically ambiguous taxa with various degrees of pathogenicity in different hosts. Previous recognition of these taxa was hampered by the lack of a distinguishing phenotypic character. Commercial test panel configurations are relatively constant over time, and as new species are defined, appropriate discriminatory tests may not be present in current test panel arrangements. While phenobiochemical tests fail to discriminate between these taxa, data presented here revealed discriminatory peaks for each species using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) methodology, suggesting that MALDI-TOF can offer rapid, reliable identification in line with current systematic classifications. Furthermore, a multiplex PCR assay was validated for rapid molecular differentiation of the spp. affecting fish. Moreover, the limitations of relying on partial 16S rRNA for discrimination of spp. and advantages of employing alternative single-copy genes and for molecular identification and classification of were demonstrated. Last, sequencing confirmed that isolates previously defined as typical motile fish-pathogenic are synonymous with, while atypical nonmotile fish-pathogenic isolates are equivalent to Fish-nonpathogenic isolates are consistent with as it is currently defined. These analyses help deconvolute the scientific literature regarding these organisms and provide baseline information to better facilitate proper taxonomic assignment and minimize erroneous identifications of isolates in clinical and research settings.

Immunogenicity of a bivalent protein as a vaccine against Edwardsiella anguillarum and Vibrio vulnificus in Japanese eel (Anguilla japonica)

“…The genus Edwardsiella was composed by three species E. tarda , E. hoshinae, and E. ictaluri before 2013 (Abayneh, Colquhoun, & Sørum, ). Some strains of E. piscicida pathogenic to fish, previously identified as E. tarda , was described in 2013 (Abayneh, Colquhoun, & Sørum, ), and a new species named E. anguillarum , also previously identified as E. tarda , was isolated from diseased eel (Reichley et al, ). Until 2016, 13 strains of E. anguillarum isolated from diseased eels in our study were first identified as E. tarda (Duan, ; Hu, ), and then all 13 strains were identified as E. anguillarum according to the method of Buján et al ().…”

“…The occurrence of bacterial diseases is the common factor that affects Japanese eel production in China. Edwardsiella anguillarum , identified as Edwardsiella tarda before 2015 (Buján et al, ; Shao et al, ) and Vibrio vulnificus (Esteve‐Gassent, Nielsen, & Amaro, ; Haenen et al, ; Reichley et al, ) are two important bacterial pathogens in eels farming, and cause serious disease and high levels of mortality in cultured eels resulting in considerable economic losses in Chinese aquaculture (Guo, ; Guo et al, ; ). These two pathogens are also recognized as causing serious diseases in a variety of fish species globally (Griffin et al, ; Jheng et al, ; Lee et al, ; Shao et al, ; Tsao et al, ).…”

Recovery and confirmation of Edwardsiella piscicida from a black crappie Pomoxis nigromaculatus (Lesueur, 1829)

“…Contemporary investigations identified multiple distinct taxa within organisms previously classified as E. tarda , each with varying pathogenicity in different hosts (Abayneh, Colquhoun, & Sørum, ; Griffin et al, ; Matsuyama, Kamaishi, Ooseko, Kurohara, & Iida, ; Wang et al, ; Yamada & Wakabayashi, ; Yang et al, ). This led to the erection of Edwardsiella piscicida (Abayneh, Colquhoun, & Sørum, ) and Edwardsiella anguillarum (Shao et al, ), which represent strains formerly categorized as typical and atypical fish pathogenic E. tarda , respectively (Buján et al, ; Reichley et al, ; Sakai, Yuasa, Sano, & Iida, ).…”

“…Since its recognition in 2013, E. piscicida has been reported from >20 species of economically and recreationally important fish (Reichley et al, ). Disease presentation varies among hosts, with a range of lesions often described as non‐specific signs of bacterial septicaemia (Griffin, Greenway, & Wise, ).…”

“…Both isolates were identified as Edwardsiella hoshinae , which has not been reported from fish. Given the documented limitations of MALDI‐TOF to differentiate the Edwardsiella (Reichley et al, ) , further molecular testing was performed.…”