Article

Immunity to Staphylococcus aureus secreted proteins protects rabbits from serious illnesses

Department of Microbiology, Medical School, University of Minnesota, Minneapolis, MN 55455, USA.
Vaccine (Impact Factor: 3.62). 06/2012; 30(34):5099-109. DOI: 10.1016/j.vaccine.2012.05.067
Source: PubMed

ABSTRACT

Staphylococcus aureus causes significant illnesses throughout the world, including toxic shock syndrome (TSS), pneumonia, and infective endocarditis. Major contributors to S. aureus illnesses are secreted virulence factors it produces, including superantigens and cytolysins. This study investigates the use of superantigens and cytolysins as staphylococcal vaccine candidates. Importantly, 20% of humans and 50% of rabbits in our TSS model cannot generate antibody responses to native superantigens. We generated three TSST-1 mutants; G31S/S32P, H135A, and Q136A. All rabbits administered these TSST-1 toxoids generated strong antibody responses (titers>10,000) that neutralized native TSST-1 in TSS models, both in vitro and in vivo. These TSST-1 mutants lacked detectable residual toxicity. Additionally, the TSST-1 mutants exhibited intrinsic adjuvant activity, increasing antibody responses to a second staphylococcal antigen (β-toxin). This effect may be due to TSST-1 mutants binding to the immune co-stimulatory molecule CD40. The superantigens TSST-1 and SEC and the cytolysin α-toxin are known to contribute to staphylococcal pneumonia. Immunization of rabbits against these secreted toxins provided complete protection from highly lethal challenge with a USA200 S. aureus strain producing all three exotoxins; USA200 strains are common causes of staphylococcal infections. The same three exotoxins plus the cytolysins β-toxin and γ-toxin contribute to infective endocarditis and sepsis caused by USA200 strains. Immunization against these five exotoxins protected rabbits from infective endocarditis and lethal sepsis. These data suggest that immunization against toxoid proteins of S. aureus exotoxins protects from serious illnesses, and concurrently superantigen toxoid mutants provide endogenous adjuvant activity.

Download full-text

Full-text

Available from: Joseph A Merriman, Dec 18, 2013
  • Source
    • "In summary, this study contributes to a growing body of literature underlining the importance of SAgs in eliciting diseases (Spaulding et al., 2013). In other studies, we have demonstrated that immunizing rabbits against SAgs protects from lethal challenge (Spaulding et al., 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The 1928 Bundaberg Disaster is one of the greatest vaccine tragedies in history. Of 21 children immunized with a diphtheria toxin-antitoxin preparation contaminated with Staphylococcus aureus, 18 developed life-threatening disease and 12 succumbed within 48 hours. Historically, the deaths have been attributed to α-toxin, a secreted cytotoxin produced by most S. aureus strains, yet the ability of the Bundaberg contaminant microbe to produce the toxin has never been verified. For the first time, we investigate the ability of the original strain to produce α-toxin and other virulence factors. We first investigate the genetic and regulatory loci mediating α-toxin expression by polymerase chain reaction and assess for production of the cytotoxin in vitro using an erythrocyte hemolysis assay. We extend this analysis to other secreted virulence factors produced by the strain and determine their sufficiency to cause lethality in New Zealand white rabbits. We demonstrate that although the strain possesses a wild-type allele for α-toxin, it must have a defective regulatory system, which is responsible for the strain's minimal α-toxin production. The strain encodes for and produces staphylococcal superantigens, including toxic shock syndrome toxin-1 (TSST-1), which is sufficient to cause lethality in patients. Our findings cast doubt on the belief that α-toxin is the major virulence factor responsible for the Bundaberg fatalities and point to the superantigen TSST-1 as the cause of the disaster.
    Full-text · Article · Oct 2015 · Microbiology
  • Source
    • "Whether MHC class II molecules play a role in induction of an inflammatory response by SAgs in adipocytes is unknown. In a previous report, we have also speculated that TSST-1 might bind to and activate CD40 [54]. Interestingly, it has been demonstrated that mature adipocytes express CD40 that can be activated, by CD40 ligand or activated CD4+ T cells, to induce secretion of inflammatory cytokines [55]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Human adipocytes may have significant functions in wound healing and the development of diabetes through production of pro-inflammatory cytokines after stimulation by gram-negative bacterial endotoxin. Diabetic foot ulcers are most often associated with staphylococcal infections. Adipocyte responses in the area of the wound may play a role in persistence and pathology. We studied the effect of staphylococcal superantigens (SAgs) on immortalized human adipocytes, alone and in the presence of bacterial endotoxin or staphylococcal α-toxin.
    Full-text · Article · Oct 2013 · PLoS ONE
  • Source
    • "For treatment of humans, however, Ab treatment would be combined with incision and drainage, unless the abscess was in a difficult-to-reach area, such as deep brain tissue. Although experimental data suggest that immunization with toxoid proteins of S. aureus exotoxins protects against serious illnesses [34], selection of S. aureus variants by a vaccine would be a concern. In addition, vaccination is costly and less efficacious in elderly patients or in patients with comorbidities, who are also most likely to develop serious S. aureus infection [35]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Background: Methicillin-resistant Staphylococcus aureus (MRSA) has become a major health threat in the United States. Staphylococcal enterotoxin B (SEB) is a potent superantigen that contributes to its virulence. High mortality and frequent failure of therapy despite available antibiotics have stimulated research efforts to develop adjunctive therapies. Methods: Treatment benefits of SEB-specific monoclonal antibody (mAb) 20B1 were investigated in mice in sepsis, superficial skin, and deep-tissue infection models. Results: Mice challenged with a SEB-producing MRSA strain developed fatal sepsis, extensive tissue skin infection, and abscess-forming deep-seeded thigh muscle infection. Animals preimmunized against SEB or treated passively with mAb 20B1 exhibited enhanced survival in the sepsis model, whereas decrease of bacterial burden was observed in the superficial skin and deep-tissue models. mAb 20B1 bound to SEB in the infected tissue and decreased abscess formation and proinflammatory cytokine levels, lymphocyte proliferation, and neutrophil recruitment. Conclusions: mAb 20B1, an SEB-neutralizing mAb, is effective against MRSA infection. mAb 20B1 protects against lethal sepsis and reduces skin tissue invasion and deep-abscess formation. The mAb penetrates well into the abscess and binds to SEB. It affects the outcome of S. aureus infection by modulating the host's proinflammatory immune response.
    Preview · Article · Aug 2013 · The Journal of Infectious Diseases
Show more