The conserved surface M-protein SiMA of Streptococcus iniae is not effective as a cross-protective vaccine against differing capsular serotypes in farmed fish

Aviles, Fabian, Zhang, Meiman May, Chan, Janlin, Delamare-Deboutteville, Jerome, Green, Timothy J., Dang, Cecile and Barnes, Andrew C. (2013) The conserved surface M-protein SiMA of Streptococcus iniae is not effective as a cross-protective vaccine against differing capsular serotypes in farmed fish. Veterinary Microbiology, 162 1: 151-159. doi:10.1016/j.vetmic.2012.08.018


Author Aviles, Fabian
Zhang, Meiman May
Chan, Janlin
Delamare-Deboutteville, Jerome
Green, Timothy J.
Dang, Cecile
Barnes, Andrew C.
Title The conserved surface M-protein SiMA of Streptococcus iniae is not effective as a cross-protective vaccine against differing capsular serotypes in farmed fish
Journal name Veterinary Microbiology   Check publisher's open access policy
ISSN 0378-1135
1873-2542
Publication date 2013-02
Year available 2012
Sub-type Article (original research)
DOI 10.1016/j.vetmic.2012.08.018
Volume 162
Issue 1
Start page 151
End page 159
Total pages 9
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2013
Language eng
Abstract Streptococcus iniae causes invasive infections in fresh and saltwater fish and occasional zoonoses. Vaccination against S. iniae is complicated by serotypic variation determined by capsular polysaccharide. A potential target for serologically cross-protective vaccines is the M-like protein SiMA, an essential virulence factor in S. iniae that is highly conserved amongst virulent strains. The present study determined how SiMA is regulated and investigated potential as a cross-protective vaccine for fish. Electrophoretic mobility shift suggested that SiMA is regulated by the multigene regulator Mgx via a binding site in the -35 region of the simA promoter. Moreover, expression of simA and mgx was highly correlated, with the highest level of simA and mgx expression during exponential growth under iron limitation (20-fold increase in relative expression compared to growth in Todd-Hewitt broth). Based on these results, a vaccination and challenge experiment was conducted in barramundi (Lates calcarifer) to determine whether SiMA is protective against S. iniae infection and cross-protective against a different capsular serotype. The challenge resulted in 60% mortality in control fish. Formalin-killed bacterins prepared from the challenge strain resulted in 100% protection, whereas bacterins prepared from a serotypically heterologous strain resulted in significantly reduced protection, even when culture conditions were manipulated to optimise SiMA expression. Moreover, recombinant SiMA protein was not protective against the challenge strain in spite of eliciting specific antibody response in vaccinated fish. Specific antibody did not increase oxidative activity or phagocytosis by barramundi macrophages. Indeed incubating S. iniae with antisera significantly reduced phagocytosis. Lack of specific-antibody mediated opsonisation in spite of 100% protection against challenge with the homologous vaccine suggests that other immune parameters result in protection of challenged fish.
Keyword Antibody response
Barramundi
Macrophage
Mgx
SiMA
Streptococcus iniae
Vaccine
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online: 1 September 2012.

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2013 Collection
School of Biological Sciences Publications
 
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Created: Wed, 14 Nov 2012, 15:56:16 EST by Gail Walter on behalf of School of Biological Sciences