“Biofilm formation and viability of Renibacterium salmoninarum under varying salinities and temperatures (7098)”

Biofilm formation and viability of Renibacterium salmoninarum under varying salinities and temperatures

introduction: bacterial kidney disease (bkd), caused by renibacterium salmoninarum (r. salmoninarum), is a serious disease affecting both wild and farmed salmonid fish worldwide. reports indicate an 80% mortality rate in pacific salmon and 40% in atlantic salmon. in norway, where it was first detected in 1980, it is classified as a notifiable disease. bkd outbreaks were reported in 2023, and well boats have been identified as a critical risk factor for horizontal disease transmission between farms during these outbreaks. as industries have prioritized biosecurity measures in recent years, it is crucial to investigate the efficacy of washing detergents and disinfectants against r. salmoninarum that can be applied to well boats and other transportation equipment. however, the efficacy of washing detergents and disinfectants is influenced by the bacteria’s ability to form autoaggregation or biofilm. the capacity of r. salmoninarum to produce autoaggregation or biofilm has not been well-documented so far.
method and aim: the bkdsafeguard project aims to determine the bacterium’s survivability, auto-aggregation, and biofilm formation abilities in different sterilized and unsterilized media (fish tank outlet water, freshwater, and seawater) and under various temperature conditions (5, 10, and 15°c) that mimic the fish farm environment.
results: the 6-week survival experiment showed that the Ct-values (14.92-17.99) of bacteria were stable and viable throughout the experiment in all the sterilized media. in unsterilized media, a marked reduction of bacteria (Ct-value: 15.55- 27.34) was observed until the 3rd week, followed by a slow increase until the 6th week (Ct-value: 15.55- 17.11). Results also indicate better viability at 5°C compared to 10 and 15°C. based on macroscopic and microscopic observations, and tube sedimentation assays, the bacterium exhibited a high tendency to form autoaggregation in fresh and seawater and a lower tendency in fish tank outlet water. the highest autoaggregation occurred at 15°c, followed by 5°c, and the lowest was at 10°c.
moreover, the biofilm formation assay showed that the bacterium can form a strong biofilm in seawater and fish tank outlet water at 15 and 10°c, but a moderate biofilm formation at 5°c. we hypothesize that autoaggregation and biofilm-forming bacteria may be more resistant to disinfection than planktonic bacteria. further work will be performed within the project to investigate the efficacy of disinfection and washing detergents on r. salmoninarum and determine the effective dose, exposure time, and optimal temperature conditions.

1. WELEKIDAN, LETEMICHAEL NEGASH, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Presenter
2. Weman Persson, David, Norwegian University of Life Sciences, Author
3. Østevik, Liv, Norwegian University of Life Sciences, Author
4. Foyn Nørstebø, Simen, Norwegian Veterinary Institute, Author