Aeromonas encheleia sp. nov., Isolated from European Eels

This study describes Aeromonas encheleia, a novel bacterial species isolated from healthy European eels in a freshwater farm in Valencia, Spain. Four phenotypically related strains were recovered from juvenile eels and characterized using DNA-DNA hybridization and extensive phenotypic testing. The strains demonstrated DNA relatedness of 0-50% to 13 previously described Aeromonas species and showed 59.4-60.8 mol% guanine-plus-cytosine content. Phenotypically, A. encheleia strains are gram-negative motile rods, oxidase and catalase positive, positive for indole production and arginine dihydrolase activity, and negative for lysine and ornithine decarboxylase. They produce acid from salicin but not from arabinose, cellobiose, or lactose, and use L-serine as a sole carbon source. The strains are ampicillin-resistant and can be distinguished from other mesophilic Aeromonas species by multiple characteristics including inability to use gluconate and differential substrate utilization patterns. Pathogenicity studies showed the strains were mostly avirulent for eels and non-pathogenic for mice, suggesting they represent part of the saprophytic microbial community associated with European eels rather than a pathogenic species.

Key findings

• Four phenotypically related bacterial strains isolated from healthy European eels constitute a new Aeromonas species with 0-50% DNA relatedness to existing Aeromonas species and ≥70% homology to each other
• A. encheleia can be distinguished from other mesophilic Aeromonas species by inability to use D-gluconate and L-arginine as sole carbon sources, inability to produce acid from lactose and cellobiose, and ampicillin resistance
• The new species is mostly avirulent for eels and non-pathogenic for mice, indicating it represents a saprophytic rather than pathogenic member of the eel microbiota
• A. encheleia has a DNA G+C content of 59.4-60.8 mol% and exhibits characteristic Aeromonas traits including oxidase, catalase positivity and glucose fermentation with variable gas production