Abstract
Piscirickettsia salmonis is the causative agent of Piscirickettsiosis, an infectious disease with a high economic impact on the Chilean salmonid aquaculture industry. This bacterium produces biofilm as a potential resistance and persistence strategy against stressful environmental stimuli. However, the in vitro culture conditions that modulate biofilm formation as well as the effect of sessile bacteria on virulence and immune gene expression in host cells have not been described for P. salmonis. Therefore, this study aimed to analyze the biofilm formation by P. salmonis isolates under several NaCl and iron concentrations and to evaluate the virulence of planktonic and sessile bacteria, together with the immune gene expression induced by these bacterial conditions in an Atlantic salmon macrophage cell line. Our results showed that NaCl and Fe significantly increased biofilm production in the LF-89 type strain and EM-90-like isolates. Additionally, the planktonic EM-90 isolate and sessile LF-89 generated the highest virulence levels, associated with differential expression of il-1β, il-8, nf-κb, and iκb-α genes in SHK-1 cells. These results suggest that there is no single virulence pattern or gene expression profile induced by the planktonic or sessile condition of P. salmonis, which are dependent on each strain and bacterial condition used.
Highlights
Chilean fish farming has gone through a tremendous expansion over the last decades including the culture of three main salmonids species such as Atlantic salmon (Salmo salar), Coho salmon (Oncorhynchus kisutch), and rainbow trout (O. mykiss)
This study aimed to determine and analyze the biofilm formation of different P. salmonis isolates under several culture conditions and to evaluate the virulence of planktonic and sessile bacteria and the immune gene expression induced by these bacterial conditions in Salmo salar head kidney (SHK-1) cells
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Summary
Chilean fish farming has gone through a tremendous expansion over the last decades including the culture of three main salmonids species such as Atlantic salmon (Salmo salar), Coho salmon (Oncorhynchus kisutch), and rainbow trout (O. mykiss). Increased fish farming has been accompanied by the development of novel infectious-contagious diseases caused mainly by viral, parasitic, and bacterial pathogens. Piscirickettsiosis is the most prevalent bacterial disease for salmonids in Chilean aquaculture [1]. This disease is caused by Piscirickettsia salmonis, a γ-proteobacteria classified into two different genogroups associated with the LF-89T (ATCC VR-1361) type strain and the Chilean isolate EM-90 [2,3]. P. salmonis secretes outer membrane vesicles (OMVs) [7], which transport several virulence proteins and toxins to the extracellular environment and within the host cell, and are involved in bacterial virulence [8]
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