The genus Edwardsiella, previously residing in the family Enterobacteriaceae and now a member of the family Hafniaceae, is currently composed of five species, although the taxonomy of this genus is still unsettled. The genus can primarily be divided into two pathogenic groups: E. tarda strains are responsible for almost all human infections, and two other species (E. ictaluri, E. piscicida) cause diseases in fish. Human infections predominate in subtropical habitats of the world and in specific geospatial regions with gastrointestinal disease, bloodborne infections, and wound infections, the most common clinical presentations in decreasing order. Gastroenteritis can present in many different forms and mimic other intestinal disturbances. Chronic gastroenteritis is not uncommon. Septicemia is primarily found in persons with comorbid conditions including malignancies and liver disease. Mortality rates range from 9% to 28%. Most human infections are linked to one of several risk factors associated with freshwater or marine environments such as seafood consumption. In contrast, edwardsiellosis in fish is caused by two other species, in particular E. ictaluri. Both E. ictaluri and E. piscicida can cause massive outbreaks of disease in aquaculture systems worldwide, including enteric septicemia in channel catfish and tilapia. Collectively, these species are increasingly being recognized as important pathogens in clinical and veterinary medicine. This article highlights and provides a current perspective on the taxonomy, microbiology, epidemiology, and pathogenicity of this increasingly important group.

In a study carried out between 2013 and 2018 in fish farms in Turkey, several putative novel species were isolated. The 16S rRNA nucleotide sequences of fourteen strains of Gram-negative rods, which were isolated from asymptomatic and symptomatic rainbow trouts (Onchorhynchus mykiss), placed them under the genus Pseudomonas. The similarity values of the concatenated nucleotide sequences of the rpoD, rpoB, gyrB and 16S rRNA genes clustered these isolates into the P. fluorescens phylogenetic group of species and into the Pseudomonas koreensis subgroup, close to Pseudomonas helmanticensis and Pseudomonas baetica. An isolate of a totally different origin, strain CCUG 67011, clustered with these isolates. Phenotypic characterization, together with the chemotaxonomic data, whole-cell MALDI-TOF MS and fatty acids methyl esters analyses were performed. The DNA G + C content was 58.7 mol% for isolate P9T and 58.8 mol% for isolate P42T. The phylogenomic analysis and whole genome nucleotide sequences of four of these isolates confirmed that the isolates P9T, P25 and P141, represent a novel species for which the name Pseudomonas anatoliensis sp. nov. is proposed, with P9T as the type strain (=CCUG 74755T = CECT 3172T). The isolates P1, P2, P10, P27, P30, P24a, P42T, P117, P139, P152 and CCUG 67011 represent another novel sècies, for which the name Pseudomonas iridis sp. nov. is proposed, with P42T as the type strain (=CCUG 74870T = CECT 3174T).

Plesiomonas shigelloides is the only species in its genus and has zoonotic importance due to the serious implications resulting from the consumption of contaminated seafood. This is the first report on the genomic features of the whole-genome sequence (WGS) of P. shigelloides strain V78, recovered from diseased rainbow trout, Oncorhynchus mykiss. The genome of P. shigelloides V78 consists of 4,478,098 base pairs (bps), which encode 3730 proteins, and has a G + C content of 51.1%. The bioinformatics analysis of WGS of V78 confirmed the presence of 121 tRNA genes and 42 rRNA genes (15 genes for 5S rRNA, 13 genes for 16S rRNA, and 14 genes for 23S rRNA). Comprehensive genome analyses revealed that the strain encodes secondary metabolites, antimicrobial resistance, and virulence genes. The strain V78 has 31 known antibiotic resistance models, which encode many antimicrobial resistances. In addition, strain V78 has 42 different virulence genes, such as adhesion, a secretion system, and motility. The digital DNA–DNA hybridization value against P. shigelloides NCTC 10360 was 74.2%, while the average nucleotide identity value was 97.1%. Based on the scrutinized analysis of genomic data, strain V78 should be considered a novel subspecies of P. shigelloides, for which Plesiomonas shigelloides subsp. oncorhynchi is proposed, with V78^T as the type strain (=LMG 33380^T=DSM 117059^T).