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BackgroundThe infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming. For effective sanitary management, the IPNV strains present in Chile need to be fully studied, characterized, and constantly updated at the molecular level.MethodsIn this study, 36 Chilean IPNV isolates collected over 6 years (2006–2011) from Salmo salar, Oncorhynchus mykiss, and Oncorhynchus kisutch were genotypically characterized. Salmonid samples were obtained from freshwater, estuary, and seawater sources from central, southern, and the extreme-south of Chile (35° to 53°S).ResultsSequence analysis of the VP2 gene classified 10 IPNV isolates as genogroup 1 and 26 as genogroup 5. Analyses indicated a preferential, but not obligate, relationship between genogroup 5 isolates and S. salar infection. Fifteen genogroup 5 and nine genogroup 1 isolates presented VP2 gene residues associated with high virulence (i.e. Thr, Ala, and Thr at positions 217, 221, and 247, respectively). Four genogroup 5 isolates presented an oddly long VP5 deduced amino acid sequence (29.6 kDa). Analysis of the VP2 amino acid motifs associated with clinical and subclinical infections identified the clinical fingerprint in only genogroup 5 isolates; in contrast, the genogroup 1 isolates presented sequences predominantly associated with the subclinical fingerprint. Predictive analysis of VP5 showed an absence of transmembrane domains and plasma membrane tropism signals. WebLogo analysis of the VP5 BH domains revealed high identities with the marine birnavirus Y-6 and Japanese IPNV strain E1-S. Sequence analysis for putative 25 kDa proteins, coded by the ORF between VP2 and VP4, exhibited three putative nuclear localization sequences and signals of mitochondrial tropism in two isolates.ConclusionsThis study provides important advances in updating the characterizations of IPNV strains present in Chile. The results from this study will help in identifying epidemiological links and generating specific biotechnological tools for controlling IPNV outbreaks in Chilean salmon farming.

Un nuevo medio de cultivo líquido para el patógeno Piscirickettsia salmonis SUMMARYPiscirickettsia salmonis is the ethiologic agent of the Salmonid Rickettsial Syndrome (SRS), which was first described in cultured Coho salmon in the south coast of Chile in 1989 and since then has been reported in different places around the world. Initially, this bacterium was described as an obligate intracellular pathogen, able to grow only in cytoplasmic vacuoles in host cell where it replicates by binary fission, so their in vitro culture is performed mainly in cell lines derived from fish. Recently, it has been demonstrated that this bacterium can grow in cell-free media containing sheep blood or fish and high levels of cysteine; however, due to the presence of cellular elements these culture media present drawbacks regarding handling, storage and high costs. We propose an artificial culture medium supplemented with an iron salt to replace the blood that is traditionally used; it reported successful growth of the bacterial reference strain and of a strain isolated from the environment, which was evaluated by optical density (OD 600 ), while purity and identity of the culture were checked by using Gram stain, immunofluorescence and PCR. Developing a blood-free culture medium facilitates the cultivation of P. salmonis and allows the growth of this bacterium in a liquid medium, which provides various microbiological and biotechnological applications.Palabras clave: cultivo líquido, Piscirickettsia salmonis.