| dc.description.abstract | Yersinia ruckeri is the aetiological agent of enteric redmouth (ERM), a disease of
salmonids, notably rainbow trout (Oncorhynchus mykiss, Walbaum). Until the
1990s, prophylaxis was achieved using a formalin-inactivated whole-cell vaccine of
a motile (= flagellin producing) Y. ruckeri strain. However, outbreaks of ERM have
since occurred in vaccinated livestock which heralded the emergence of a new
biogroup. In addition to giving a negative result for the Voges–Proskauer (VP)
reaction and the production of an extracellular lipase, strains responsible for the
majority of these new outbreaks in vaccinated stock were non-motile and unable to
produce detectable flagellin. It was the aim of this study to determine what
protective role flagellin may have towards Y. ruckeri infection, both as a component
of the whole-cell vaccine and as a vaccine in itself (i.e. sub-unit vaccine).
Results showed that protection against bacterial challenge, either with a motile or
non-motile Y. ruckeri strain, was not entirely dependent on the presence of flagellin
within the whole-cell vaccine. On the other hand, administering native flagellin (50
μg/fish) via intraperitoneal injection (without adjuvant) resulted in excellent levels
of protection (relative percent survival = 100%) against challenge 28 days postvaccination
with a flagellin-producing (YR1) or flagellin-devoid (R1) Y. ruckeri
strain. Use of recombinant flagellin (r-flagellin) as a vaccine again confirmed the
protective properties against challenge with both YR1 and R1 strains, even at lower
concentrations i.e. 10 μg/fish. Protection was also conferred after a relatively short
period of time (14 days) without any detrimental effect on health or weight of the
fish. Thus flagellin has the potential to be an efficacious, non-specific sub-unit
vaccine for rainbow trout.
Analysis of whole cell proteins by SDS-PAGE from both motile and non-motile
isolates demonstrated that highly virulent EX5 isolates which caused disease in
vaccinated livestock were overexpressing a 30 to 40 kDa protein. 2D SDS-PAGE
and Maldi-tof mass spectrometry identified this protein as outer membrane protein A
(OmpA). However, attempts to disrupt the gene encoding the OmpA protein (ompA)
using transposon mutagenesis and PCR screening failed to isolate a mutant with a
transposon within the gene of interest (ompA::Tn-RL27). | |
