Tenacibaculosis is one of the most threatening bacterial infections in aquaculture, limiting the farming of various commercially important fish species worldwide. In Chilean salmonid farming, Tenacibaculum maritimum has been identified as one of the main causative agents of the disease, yet little is known about the genetic variability of local isolates. This study aimed to characterize 40 Chilean isolates of Tenacibaculum maritimum obtained from Salmo salar, Oncorhynchus mykiss, and Genypterus chilensis during disease outbreaks from 2020 to 2024. Two molecular techniques were employed: multiplex PCR for O-antigen typing (Lopez et al., 2022) and REP-PCR for genetic fingerprinting (Fernández-Alvarez et al., 2018).
Phenotypic analysis confirmed that the isolates show homogeneity among the Chilean isolates, which is not correlated with the origin of the isolate or host. The isolates were filamentous Gram-negative rods, catalase- and oxidase-positive, with gliding motility and no flexirubin pigments. Colonies on FMM agar were pale yellow, flat, and irregular.
Molecular serotyping revealed four profiles: 1-0 (n=3), 3-1 (n=3), 3-2 (n=2), and 4-0 (n=32), with serotype 4-0 predominating. REP-PCR identified three known patterns related with REP 3 from O. mykiss and S. salar and two novel patterns. Thirty-five isolates grouped under REP7 (including 34 from S. salar and one from G. chilensis), and two isolates from S. salar shared a new REP6 profile associated with serotype 1-0 and the reference strain NCIMB 2154T.
These findings suggest higher genetic variability among Chilean isolates than previously detected by serotyping alone. These results expand the current knowledge about the epidemiology of the fish pathogen Tenacibaculum maritimum, by incorporating new data, especially regarding the molecular diversity affecting cultured fish. Also allow us to recommend preventive measures, specifically vaccines, should be developed according to dominant isolates and with specificity to each farm.