Abstract

Piscirickettsiosis is a systemic infectious disease caused by Piscirickettsia salmonis, a Gram-negative, biofilm-forming bacterium capable of infecting the main salmonid species farmed in Chile. The initial stages of P. salmonis infection occur in the mucous membranes of the skin, gills, and intestine before spreading systemically. At the intestinal level, several pathogenic bacteria can disrupt the functionality of the epithelial barrier as an infection mechanism, associated with alterations in the expression of immune genes and intercellular junctions. The aim of this study was to determine in vitro the effect of P. salmonis infection in both sessile and planktonic conditions on the morpho functionality of the intestinal epithelial cell line RTgutGC of rainbow trout. Thus, the effect of P. salmonis infection on immune gene expression and intercellular junctions was evaluated using RT-qPCR, intercellular junction protein levels via Western blot, transepithelial resistance (TEER) modulation, cytotoxicity, and ZO-1 localization through immunofluorescence. The results indicate that P. salmonis LF-89 and EM-90 in both sessile and planktonic conditions significantly modulate the expression of il-8, il-1β, tgf-β, and zo-1, claudin-3, and E-cadherin. Interestingly, alterations in the levels of Claudin-3 and E-cadherin, associated with the altered immunolocalization of ZO-1 after the infection with P. salmonis, were detected. Importantly, an increase in bacterial translocation associated with a decrease in the TEER value, from the first 12 h post-infection, was measured. These findings suggest that P. salmonis modulates the expression of genes and proteins related to intercellular junctions, modifying the epithelial morpho-functionality, which could allow bacterial translocation in the early stages of infection.