Plant-based compounds may reduce virulence of SRS
Published
The potential use of polyphenolic compounds as an alternative to antibiotics to tackle SRS (salmonid rickettsial septicaemia) has shown promising results in lab experiments in Chile, reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.
Piscirickettsia salmonis, which causes SRS, is the pathogen that has most affected the Chilean salmon industry for over 30 years and is also becoming an increasing issue in Ireland, where a widespread and previously less pathogenic strain of P. salmonis is increasing in virulence. SRS is also a problem in Canada, and isolated outbreaks have been reported in Scotland.
The heavy use of antibiotics to combat SRS has led scientists at Santiago University to look at antivirulence therapy is an alternative to reduce the virulence of pathogens without affecting their growth.
Plant extracts
In their most recent study, they evaluated the capacity of the polyphenolic compounds, quercetin and silybin, to reduce the intracellular replication of P. salmonis in salmon head kidney-1 (SHK-1) cells. Quercetin is a plant pigment found in many fruits and vegetables, and silybin is the major active constituent of silymarin, a standardised extract of milk thistle.
The researchers used three different infection protocols: co-incubation for 24 hours, pre-incubation for 24 hours prior to infection, and post-incubation for 24 hours after infection.
In addition, the effect of co-incubation in rainbow trout intestinal epithelial cells (RTgutGC) and the effect on the phagocytic capacity of SHK-1 cells were evaluated. Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells, but P. salmonis has the ability to internalise itself in phagocytic cells and replicate inside them.
Decreased replication
The researchers discovered that quercetin and silybin decreased the intracellular replication of P. salmonis in SHK-1 cells when they were co-incubated for 24 hours. However, they did not have the same effect in RTgutGC cells.
On the other hand, both compounds decreased the phagocytosis of SHK-1 cells during co-incubation.
“These results could indicate that the compounds affect the phagocytosis process of phagocytic cells, which are the target cells of P. salmonis,” concluded the researchers.
“Future experiments are necessary to elucidate the mechanism by which these compounds have this effect, which could be an interaction with proteins of the bacteria, of the cells, or both. Finally, these results are promising to evaluate the effect of the administration of these compounds in Salmo salar (Atlantic salmon) against a challenge with P. salmonis as a possible treatment.”
Read the full study titled “Quercetin and Silybin Decrease Intracellular Replication of Piscirickettsia salmonis in SHK-1 Cell” here.
