Abstract
BackgroundStaphylococcus aureus is unrestrictedly found in humans and in animal species that maintain thermal homeostasis. Inadequate cleaning of processing equipment or inappropriate handling can contaminate processed food and cause severe food poisoning. Staphylococcal enterotoxin B (SEB), a potent superantigenic exotoxin, is produced by 50% of clinical isolates of S. aureus and is associated with massive food poisoning and with the induction of toxic shock syndrome.ResultsA gene sequence encoding a recombinant SEB (rSEB), devoid of superantigenic activity, was successfully cloned and expressed in a cytoplasmic or a secreted form in the food-grade lactic acid bacterium Lactococcus lactis. The recombinant protein detected in the cytoplasm or in the culture medium exhibited the expected molecular mass and was recognized by a SEB-polyclonal antibody. Oral immunization with the recombinant L. lactis strains induced a protective immune response in a murine model of S. aureus infection. Immunized mice survived intraperitoneal challenge with an S. aureus SEB-producer strain. Counts of S. aureus in the spleen of rSEB-immunized mice were significantly reduced. The rSEB-immunized mice showed significant titers of anti-SEB IgA and IgG in stools and serum, respectively. Both recombinant L. lactis strains were able to elicit cellular or systemic immune responses in mice, with no significant difference if rSEB was produced in its cytoplasmic or secreted form. However, recombinant L. lactis expressing the cytoplasmic rSEB increased the survival rate of the challenged mice by 43%.ConclusionsThese findings show the vaccine efficacy of L. lactis carrying an attenuated SEB, in a murine model, following lethal S. aureus challenge.
Highlights
Staphylococcus aureus is unrestrictedly found in humans and in animal species that maintain thermal homeostasis
The pCYT:recombinant SEB (rSEB) vector harbors a transcriptional fusion between the ribosomebinding site (RBSusp45) of the usp45 gene [22] and the DNA sequence encoding the mature moiety of rSEB, and the pSEC:rSEB harbors a transcriptional fusion between RBSusp45 and the DNA sequence encoding the signal peptide (SPusp45) of Usp45 plus rSEB
A single band with the expected size for rSEB (27 kDa) – available in the Protein families database Pfam [http://www.sanger.ac.uk/ Software/Pfam/search.shtml] - was identified in the cell pellet (Figure 1, lane 2) and in culture supernatants (Figure 1, lane 4) of induced L. lactis and L. lactis, respectively
Summary
Staphylococcus aureus is unrestrictedly found in humans and in animal species that maintain thermal homeostasis. Staphylococcal enterotoxin B (SEB), a potent superantigenic exotoxin, is produced by 50% of clinical isolates of S. aureus and is associated with massive food poisoning and with the induction of toxic shock syndrome. Staphylococcus aureus is a Gram-positive opportunistic pathogen of humans and warm-blooded animals, and is part of the commensal microbiota of the skin and nares in a significant proportion of the human population It is a leading cause of bloodstream, lower respiratory tract, and skin and soft-tissue infections. S. aureus has a wide range of virulence factors, including superantigens such as staphylococcal enterotoxins (SEs). These heatstable toxins cause a self-limiting gastrointestinal intoxication, but parenteral exposures can cause a potentially fatal toxic shock syndrome [1,2,3]. Various vaccination regimens of an attenuated SEB mutant protein containing L45R, Y89A and Y94A were effective in a primate model against aerosolized wild-type SEB, with a correlation between survival of rhesus monkeys, antibody titers, and neutralizing antibody [11]
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