Isolation, identification, virulence potential and genomic features of Tenacibaculum piscium isolates recovered from Chilean salmonids.

Tenacibaculum piscium, a gram-negative bacterium isolated from the skin ulcers of sea-farmed fish, has only been described in Norway. In the present study, we examined 16 Chilean Tenacibaculum isolates recovered from different organs in moribund and dead Atlantic salmon (Salmo salar), Rainbow trout (Oncorhynchus mykiss) and Coho salmon (Oncorhynchus kisutch) cultured at different fish farms between 2014 and 2018. The present study applied biochemical, phenotypic, fatty acid and whole-genome sequence-based analyses to confirm the taxonomic status of the Chilean isolates. The obtained results are the first to confirm the presence of T. piscium in Chile and in Coho salmon, thus extending the recognized geographical and species distribution of this bacterium. Subsequent bath-challenge assays in Atlantic salmon utilizing three T. piscium isolates obtained from different hosts resulted in low cumulative mortality (i.e. 0-35%), even after exposure to an unnaturally high concentration of bacterial cells (i.e. > 107 cells/ml). However, scale loss and frayed fins were observed in dead fish. In silico whole-genome analysis detected various genes associated with iron acquisition, encoding of the type IX secretion system and cargo proteins, resistance to tetracycline and fluoroquinolones and stress responses. These data represent an important milestone towards a better understanding on the genomic repertoire of T. piscium.

First report and characterization of Tenacibaculum maritimum isolates recovered from rainbow trout (Oncorhynchus mykiss) farmed in Chile.

The present study reports on the first isolation of Tenacibaculum maritimum in rainbow trout (Oncorhynchus mykiss) farmed in Chile. In March 2020, two cages raising rainbow trout (~250 g) in the Los Lagos Region suffered a disease outbreak. In total, 17,554 fish died (3.5%-4.8% accumulated mortality). Microbiological analysis of the diseased fish obtained two representative isolates (i.e. Tm-035 and Tm-036). These were obtained from the external gross skin lesions-typical of tenacibaculosis-of two fish. Phenotyping, PCR tests and sequencing of the 16S rRNA and housekeeping genes confirmed the isolates as T. maritimum. The pathogenic potential of Tm-035 was further assessed by bath challenging Atlantic salmon (Salmo salar), which killed 70 ± 15% of fish within 11 days. Dead fish presented the same external clinical signs as did the farmed rainbow trout specimens. This research further broadens the known host distribution of this pathogen. Furthermore, the virulence experiments demonstrated that T. maritimum does not have a specific host. Additional studies are needed to evaluate the risk of T. maritimum for the O. mykiss farming industry.