scholarly journals Aeromonas salmonicida type III secretion system-effectors-mediated immune suppression in rainbow trout ( Oncorhynchus mykiss )

2017 ◽  
Vol 60 ◽  
pp. 334-345 ◽  
Author(s):  
F.C. Origgi ◽  
O. Benedicenti ◽  
H. Segner ◽  
U. Sattler ◽  
T. Wahli ◽  
...  
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Immune Suppression ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Aeromonas Salmonicida ◽  
Type Iii ◽  
Rainbow Trout Oncorhynchus Mykiss

Attenuated virulence of an Aeromonas salmonicida subsp. salmonicida type III secretion mutant in a rainbow trout model

Microbiology ◽  
2005 ◽  
Vol 151 (6) ◽  
pp. 2111-2118 ◽  
Author(s):  
Sarah E. Burr ◽  
Dmitri Pugovkin ◽  
Thomas Wahli ◽  
Helmut Segner ◽  
Joachim Frey
Keyword(s):  
Rainbow Trout ◽  
Histological Examination ◽  
Type Iii Secretion ◽  
Systemic Disease ◽  
Type Iii Secretion System ◽  
Systemic Infection ◽  
Secretion System ◽  
Aeromonas Salmonicida ◽  
Blood Leukocytes ◽  
Type Iii

Aeromonas salmonicida subsp. salmonicida is the causative agent of furunculosis, a severe systemic disease affecting salmonid fish. This bacterium contains a type III protein secretion system that is responsible for the secretion and translocation of the ADP-ribosylating toxin, AexT, into the cytosol of fish cells. This study showed that inactivation of the type III secretion system by marker-replacement mutagenesis of the gene ascV, which encodes an inner-membrane component of the type III secretion system, attenuated virulence in a rainbow trout model. The isogenic ascV deletion mutant was phagocytosed by peripheral blood leukocytes but the wild-type (wt) A. salmonicida subsp. salmonicida isolate was not. Histological examination of fish experimentally infected with the wt bacterium revealed extensive tissue necrosis and bacterial aggregates in all organs examined, including the heart, kidney and liver, indicating that the isolate established a systemic infection. Cumulative mortality of fish experimentally infected with the wt bacterium reached 88 %. In contrast, no mortality was observed among fish infected with the same dose of the ascV mutant, and histological examination of fish infected with this strain revealed healthy organs. The results indicate that the type III secretion system of A. salmonicida subsp. salmonicida is required to establish systemic infection.

scholarly journals Evidence for a Type III Secretion System in Aeromonas salmonicida subsp. salmonicida

2002 ◽  
Vol 184 (21) ◽  
pp. 5966-5970 ◽  
Author(s):  
Sarah E. Burr ◽  
Katja Stuber ◽  
Thomas Wahli ◽  
Joachim Frey
Keyword(s):  
Type Iii Secretion ◽  
Type Strain ◽  
Wild Type Strain ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Aeromonas Salmonicida ◽  
Broad Host Range ◽  
Wild Type ◽  
Secretion Systems ◽  
Type Iii

ABSTRACT Aeromonas salmonicida subsp. salmonicida, the etiological agent of furunculosis, is an important fish pathogen. We have screened this bacterium with a broad-host-range probe directed against yscV, the gene that encodes the archetype of a highly conserved family of inner membrane proteins found in every known type III secretion system. This has led to the identification of seven open reading frames that encode homologues to proteins functioning within the type III secretion systems of Yersinia species. Six of these proteins are encoded by genes comprising a virA operon. The A. salmonicida subsp. salmonicida yscV homologue, ascV, was inactivated by marker replacement mutagenesis and used to generate an isogenic ascV mutant. Comparison of the extracellular protein profiles from the ascV mutant and the wild-type strain indicates that A. salmonicida subsp. salmonicida secretes proteins via a type III secretion system. The recently identified ADP-ribosylating toxin AexT was identified as one such protein. Finally, we have compared the toxicities of the wild-type A. salmonicida subsp. salmonicida strain and the ascV mutant against RTG-2 rainbow trout gonad cells. While infection with the wild-type strain results in significant morphological changes, including cell rounding, infection with the ascV mutant has no toxic effect, indicating that the type III secretion system we have identified plays an important role in the virulence of this pathogen.

scholarly journals Expression of and secretion through the Aeromonas salmonicida type III secretion system

Microbiology ◽  
2006 ◽  
Vol 152 (5) ◽  
pp. 1275-1286 ◽  
Author(s):  
Roger O. Ebanks ◽  
Leah C. Knickle ◽  
Michel Goguen ◽  
Jessica M. Boyd ◽  
Devanand M. Pinto ◽  
...  
Keyword(s):  
Growth Temperature ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Growth Conditions ◽  
Secretion System ◽  
Aeromonas Salmonicida ◽  
Effector Proteins ◽  
Type Iii ◽  
Low Calcium

Aeromonas salmonicida subsp. salmonicida is the aetiological agent of furunculosis, a disease of farmed and wild salmonids. The type III secretion system (TTSS) is one of the primary virulence factors in A. salmonicida. Using a combination of differential proteomic analysis and reverse transcriptase (RT)-PCR, it is shown that A. salmonicida A449 induces the expression of TTSS proteins at 28 °C, but not at its more natural growth temperature of 17 °C. More modest increases in expression occur at 24 °C. This temperature-induced up-regulation of the TTSS in A. salmonicida A449 occurs within 30 min of a growth temperature increase from 16 to 28 °C. Growth conditions such as low-iron, low pH, low calcium, growth within the peritoneal cavity of salmon and growth to high cell densities do not induce the expression of the TTSS in A. salmonicida A449. The only other known growth condition that induces expression of the TTSS is growth of the bacterium at 16 °C in salt concentrations ranging from 0·19 to 0·38 M NaCl. It is also shown that growth at 28 °C followed by exposure to low calcium results in the secretion of one of the TTSS effector proteins. This study presents a simple in vitro model for the expression of TTSS proteins in A. salmonicida.

scholarly journals Contribution of the type III secretion system (TTSS) to virulence of Aeromonas salmonicida subsp. salmonicida

Microbiology ◽  
2006 ◽  
Vol 152 (6) ◽  
pp. 1847-1856 ◽  
Author(s):  
A. Dacanay ◽  
L. Knickle ◽  
K. S. Solanky ◽  
J. M. Boyd ◽  
J. A. Walter ◽  
...  
Keyword(s):  
Atlantic Salmon ◽  
Type Iii Secretion ◽  
Parental Strain ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Aeromonas Salmonicida ◽  
Gene Encoding ◽  
Membrane Pore ◽  
Type Iii ◽  
H Nmr

The recently described type III secretion system (TTSS) of Aeromonas salmonicida subsp. salmonicida has been linked to virulence in salmonids. In this study, three TTSS effector genes, aexT, aopH or aopO, were inactivated by deletion, as was ascC, the gene encoding the outer-membrane pore of the secretion apparatus. Effects on virulence were assayed by live challenge of Atlantic salmon (Salmo salar). The ΔascC mutant strain was avirulent by both intraperitoneal (i.p.) injection and immersion, did not appear to establish a clinically inapparent infection and did not confer protection from subsequent rechallenge with the parental strain. 1H NMR spectroscopy-based metabolite profiling of plasma from all fish showed significant differences in the metabolite profiles between the animals exposed to the parental strain or ΔascC. The experimental infection by immersion with ΔaopO was indistinguishable from that of the parental strain, that of ΔaexT was delayed, whilst the virulence of ΔaopH was reduced significantly but not abolished. By i.p. injection, ΔaexT, ΔaopH and ΔaopO caused an experimental disease indistinguishable from that of the parental strain. These data demonstrate that while the TTSS is absolutely essential for virulence of A. salmonicida subsp. salmonicida in Atlantic salmon, removal of individual effectors has little influence on virulence but has a significant effect on colonization. The ΔascC i.p. injection data also suggest that in addition to host invasion there is a second step in A. salmonicida pathogenesis that requires an active TTSS.

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