Abstract

Piscirickettsiosis is a fish disease caused by the facultative intracellular bacterium,Piscirickettsia salmonis. Even though entry routes ofP. salmonisin fish are not fully clear yet, the skin seems to be the main portal in some salmonid species. Despite the importance of fish mucous skin barrier in fighting waterborne pathogens, the interaction between salmonid skin mucus and the bacterium is unknown. This study seeks to determine the in vitro changes in the growth of two ChileanP. salmonisstrains (LF-89-like and EM-90-like genotypes) and the type strain LF-89(T)under exposures to skin mucus fromSalmo salarandOncorhynchus mykiss, as well as changes in the cytotoxic effect ofP. salmonison the SHK-1 cells following exposures. The results suggest that the growth of threeP. salmonisstrains was not significantly negatively affected under exposures to skin mucus (adjusted at 100 mu g total protein ml(-1)) ofO. mykiss(69 +/- 18 U lysozyme ml(-1)) andS. salar(48 +/- 33 U lysozyme ml(-1)) over time. However, the cytotoxic effect ofP. salmonis, pre-exposed to salmonid skin mucus, on the SHK-1 cell line was reliably identified only towards the end of the incubation period, suggesting that the mucus had a delaying effect on the cytotoxic response of the cell line to the bacterium. These results represent a baseline knowledge to open new avenues of research intended to understand howP. salmonisfaces the fish mucous skin barrier.