phoP, SPI1, SPI2 and aroA mutants of Salmonella Enteritidis induce a different immune response in chickens
Elsheimer-Matulova et al. Veterinary Research
phoP, SPI1, SPI2 and aroA mutants of Salmonella Enteritidis induce a different immune response in chickens
Marta Elsheimer-Matulova 0
Karolina Varmuzova 0
Kamila Kyrova 0
Hana Havlickova 0
Frantisek Sisak 0
Masudur Rahman 0
Ivan Rychlik 0
0 Veterinary Research Institute , Hudcova 70, 621 00, Brno , Czech Republic
Poultry is the most frequent reservoir of non-typhoid Salmonella enterica for humans. Understanding the interactions between chickens and S. enterica is therefore important for vaccine design and subsequent decrease in the incidence of human salmonellosis. In this study we therefore characterized the interactions between chickens and phoP, aroA, SPI1 and SPI2 mutants of S. Enteritidis. First we tested the response of HD11 chicken macrophage-like cell line to S. Enteritidis infection monitoring the transcription of 36 genes related to immune response. All the mutants and the wild type strain induced inflammatory signaling in the HD11 cell line though the response to SPI1 mutant infection was different from the rest of the mutants. When newly hatched chickens were inoculated, the phoP as well as the SPI1 mutant did not induce an expression of any of the tested genes in the cecum. Despite this, such chickens were protected against challenge with wild-type S. Enteritidis. On the other hand, inoculation of chickens with the aroA or SPI2 mutant induced expression of 27 and 18 genes, respectively, including genes encoding immunoglobulins. Challenge of chickens inoculated with these two mutants resulted in repeated induction of 11 and 13 tested genes, respectively, including the genes encoding immunoglobulins. In conclusion, SPI1 and phoP mutants induced protective immunity without inducing an inflammatory response and antibody production. Inoculation of chickens with the SPI2 and aroA mutants also led to protective immunity but was associated with inflammation and antibody production. The differences in interaction between the mutants and chicken host can be used for a more detailed understanding of the chicken immune system.
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Introduction
Non-typhoid Salmonella enterica serovars are among
the most common causative agents of food-borne
diseases worldwide [1]. Since poultry is the most frequent
reservoir of salmonellosis for humans, vaccination of
chickens is understood as an effective measure to
decrease S. enterica incidence in humans. Currently,
construction of attenuated vaccine strains of S. enterica
is not an issue and many different mutants have been
tested in mice, chickens and even humans [2-7].
However, the main dilemma is which mode of attenuation to
choose out of the many possibilities [8]. More detailed
information on host response to S. enterica infection or
vaccination is therefore needed. Such information can be
obtained either by generating chickens with knocked out
genes involved in innate or acquired immune response
or by preparing S. enterica mutants with clearly defined
defects in pathogenesis and analysis of chicken immune
response. Since the former possibility is still an issue in
chickens, the latter approach represents a feasible
alternative.
Mutants with clearly different defects in Salmonella
pathogenesis include those with deletions in aroA, phoP,
SPI1 or SPI2. Reduced virulence of aroA mutants can be
explained by their inability to produce aromatic
compounds as well as having a high sensitivity to serum
[2,9]. phoP mutants belong to the most attenuated ones
as they fail to survive inside phagocytic cells [10],
perhaps due to their high sensitivity to acidification and
host antimicrobial peptides [11]. However, phoP mutants
also exhibit intracellular overgrowth in fibroblasts [12].
Recently, mutants defective in virulence genes specific to
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S. enterica such as those localized on the Salmonella
pathogenicity island (SPI) 1 and SPI2 have been
successfully tested [5,13]. SPI1 mutants are impaired in invading
non-professional phagocytes while SPI2 mutants are
unable to survive intracellularly for a prolonged time
[14-17]. SPI1 mutants are also defective in induction of
apoptosis in macrophages [18,19]. Interestingly, when
we recently used SPI1 and SPI2 mutants of S. enterica
serovar Enteritidis for vaccination of chickens, higher
antibody levels were observed in chickens vaccinated
with the SPI2 mutant than in chickens vac (...truncated)