Functional and molecular assessment of the role of toxic shock syndrome toxin-1, staphylococcal enterotoxin A, and staphylococcal enterotoxin B in the pathogenesis of toxic shock syndrome
Creators: name: De Boer, Monica Lynn
Publisher: name: University of British Columbia
Year: 2009

description: Staphylococcus aureus produces exoproteins including toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) which have been implicated in causing an acute multisystem disease called toxic shock syndrome (TSS). These toxins belong to the family of proteins known as superantigens. Superantigens cause profound immunological disturbances which are believed to underly the mechanisms causing TSS upon infection with toxigenic strains of S. aureus. Production of TSST-1, SEA and SEB are examples of variable genetic traits in that they are produced by some S. aureus isolates but not others. Certain toxin combinations are more prevalent than others. For example, SEA and TSST-1 are frequently co-produced among menstrual TSS isolates, whereas TSST-1 and SEB appear to rarely, if ever, be co-produced. The nature of these interactions on both functional and molecular levels was examinined in this thesis. It was hypothesized that co-production of SEA and TSST-1 might yield a more virulent strain than production of TSST-1 alone, providing a putative explanation for why TSST- 1+/SEA+ strains are associated with the majority of menstrual TSS cases. To test this hypothesis, a TSST-1+/SEA" derivative of a TSST-1+/SEA+ clinical strain was constructed by the method of plasmid integration. Introduction of the TSST-1+/SEA+ and TSST- 1+/SEA" strains into a tampon-associated vaginal infection model of TSS and a Dgalactosamine sensitized mouse model of lethal shock however did not demonstrate any detectable differences in lethality or morbidity between the strains. In addition, in vitro analyses revealed that the culture filtrate from the SEA" mutant did not differ in its ability to induce TNFa secretion from rabbit splenocytes or stimulate T cell proliferation at low dilutions when compared to the TSST-1 VSEA" strain. This suggests that production of SEA with TSST-1 in this strain does not increase the virulence of S. aureus. The molecular basis of mutually exclusive production of TSST-1 and SEB in S. aureus was examined. Analysis of TSST-1+ isolates indicated that 8 of 8 TSST-1+ isolates had sequences homologous with seb, even though SEB was not produced. PCR analysis with primers that targeted various regions of seb failed to amplify the expected PCR product, suggesting that a full SEB coding sequence is not present. Hybridization of restriction fragments with TSST-1 and SEB genetic element probes suggested that tst was located in close proximity to SEB genetic element sequences on the chromosome. DNA similarities between TSST-1+ and SEB+ isolates were also found upon hybridization with SEB genetic element probes. These observations could suggest that the SEB genetic element carries a preferred site of TSST-1 genetic element insertion. Upon insertion, the TSST-1 genetic element may interfere with the expression of SEB in as yet some unidentifed manner. Alternatively, the TSST-1 and SEB genetic elements may share a common point of insertion in the S. aureus chromosome linked to DNA sequences homologous to the SEB genetic element. Insertion of one genetic element carrying one of the toxin genes may inhibit the insertion of the other genetic element carrying the alternate toxin gene.