Yersinia Ruckeri O1 Biotype Research Articles

Citrus flavonoids, β-Glucan and organic acid feed additives decrease relative risk during Yersinia ruckeri O1 biotype 2 infection of rainbow trout (Oncorhynchus mykiss).

Whether through direct supplementation of bacteria or by prebiotic supplementation thought to favour subsets of bacteria, modulation of gut microbiota constitutes an important and promising alternative to the use of prophylactic and growth promoting antibiotics in worldwide aquaculture. We fed a commercial base feed, alone or supplemented with either proprietary β-glucan, β-glucan and organic acids, citrus flavonoid or yeast cell wall supplements, to rainbow trout over a period of four weeks. Fish from each feed group were then subjected to experimental, waterborne infection with Yersinia ruckeri O1 biotype 2. Following experimental feeding, the β-glucan and organic acids supplemented group showed significantly improved feed conversion and lipid efficiency ratios. Furthermore, the β-glucan, β-glucan and organic acids and citrus flavonoid supplements proved to significantly reduce the risk of mortality in rainbow trout during experimental infection as shown by hazard ratio analysis. Resulting in 33.2%, 30.6% and 30.5% reduction in risk relative to the non-supplemented base feed, respectively, these three supplements show a promising potential either as stand-alone feed supplements, or as components in complex feed formulations.

Effects of fish size and route of infection on virulence of a Danish Yersinia ruckeri O1 biotype 2 strain in rainbow trout (Oncorhynchus mykiss)

The comparative virulence of Yersinia ruckeri serotype O1 biotype 2 strain 07111224 from a Danish outbreak of enteric redmouth disease in rainbow trout (Oncorhynchus mykiss) was investigated in different sizes of rainbow trout (5, 19, 25 and 52 g) using a panel of challenge methods (bath, intraperitoneal (IP) injection, anal intubation and cohabitation).The results show that Y. ruckeri 07111224 is virulent enough to successfully cause mortality in 5–52 g rainbow trout through three different infection routes (bath, IP injection and anal intubation), and strongly suggests that susceptibility to Y. ruckeri infection is dependent on fish size. Bath challenge (108 CFU/ml) caused 79% mortality in 5 g fish, while the mortality in 19–52 g fish was approximately 26%. IP injection challenges (105–106 CFU/individual) resulted in high mortalites in fish of all sizes. Anal intubation challenges (109 CFU/individual) induced 82% mortality in 5 g fish and decreased with increasing fish weight. Finally, cohabitation challenges induced 45% mortality in 5 g test fish when test fish were cohabitated 1:1 with shedder fish, while mortalities in test fish of five other challenge groups were lower (5–25%). Statistical models were fit to the data from each challenge model. The model parameter predictions suggests statistically significant effects of fish weight for bath, IP and anal intubation challenges. Furthermore, they highlight the importance of the ratio of shedders to test fish in cohabitation challenges and of the challenge doses, in particular for the IP challenge model.

Development of a Yersinia ruckeri O1 biotype 2 waterborne challenge model for future ERM vaccine testing in rainbow trout

Development of a Yersinia ruckeri O1 biotype 2 waterborne challenge model for future ERM vaccine testing in rainbow trout

Comparative evaluation of administration methods for a vaccine protecting rainbow trout against Yersinia ruckeri O1 biotype 2 infections

Numerous outbreaks of enteric red mouth disease (ERM) caused by Yersinia ruckeri O1 biotype 2 in rainbow trout farms are currently being recorded despite established vaccination procedures against this disease. This could indicate that the currently used application of single immersion vaccination (using a commercial vaccine AquaVac® RELERA™) does not provide full protection. We elucidated by a controlled duplicated experiment if different vaccine administration methods can improve level and extent of protection. Rainbow trout, Oncorhynchus mykiss were vaccinated by: (1) a single immersion in bacterin diluted 1:10 for 30s (only primary vaccination); (2) two times 30s immersion (primary immersion vaccination followed by booster immersion vaccination 1 month later); (3) a single i.p. injection (only primary vaccination); (4) immersion vaccination followed by injection booster 1 month later; (5) a single 1h bath in bacterin diluted 1:2000; and (6) immersion (30s, 1:10) plus booster (1h in diluted 1:2000 vaccine) 5 months later). Injection challenge experiments were performed 3, 5 and 7 months post primary vaccination with 8.5×106CFU/fish, 10.6×106CFU/fish and 1×108CFU/fish, respectively. In the first challenge trial, control fish exhibited a mortality of 76%, one time immersion vaccination had a mortality of 37%, two times immersion vaccinated fish had a 4% mortality, the one-time injection vaccinated group showed a mortality of 2% and the immersion plus injection boostered fish showed no mortality at all. When rainbow trout were challenged 5 months post primary vaccination, 26% mortality occurred in control fish, 21% in one time immersion group, 12% in two times immersion group, 5% in the one-time injection vaccinated group whereas immersion plus injection boostered fish again showed no mortality at all. When challenged 7 months post vaccination, one-time immersion vaccinated were not protected at all compared to the control group whereas injection vaccinated fish showed lower mortality (17%) compared to booster immersed fish (32% mortality) which was still better than un-vaccinated controls (44% mortality). It was noteworthy that a diluted bacterin (1:2000 for 1h after 5 months post primary vaccination) booster showed the same effect as a booster with 1:10 bacterin dilution for 30s applied 1 month after primary vaccination. Antibody levels showing significant elevations 28 days post challenge in vaccinated fish point to this immune parameter as a protective element. The superior and extended protection offered by booster vaccination or simply injection is noteworthy and may be applied in future vaccination strategies at farm level.