In vitro studies of toxic shock toxin-1-secreting staphylococcus aureus and implications for burn care in children

Background: The main etiologic agent of toxic shock syndrome is the toxic shock syndrome toxin-1 (TSST-1) protein secreted by Staphylococcus aureus. Diagnosis of toxic shock syndrome is difficult and is significantly underdiagnosed in young children with burns due to the nonspecific presentation coupled with a rapid deterioration in patient condition. Methods: The lytic and cytolytic activity of a number of clinical and laboratory TSST-1-positive strains of methicillin-susceptible S. aureus (101, 253, 279 and RN4282, respectively) and Pseudomonas aeruginosa PAO1 strain were tested in vitro using an assay designed to assess the relative exotoxin activity of bacteria using phospholipid vesicles and a T cell toxicity assay. In addition, the activity of lytic exotoxins such as δ-toxin and the secretion of nonlytic TSST-1 toxin from S. aureus was measured using the vesicle assay and Western blotting over the 20-hour growth of TSST-1-positive S. aureus culture. Results: Both the vesicle and T cell assays suggest a lytic exotoxin-mediated mechanism of vesicle rupture and T cell death, with high levels of vesicle lysis and T cell toxicity. It is important to note that the clinical TSST-1-positive methicillin-susceptible S. aureus strains exhibited lytic exotoxin production as well as TSST-1 expression as confirmed by Western blot. Conclusion: We suggest that there is no correlation between the expression of TSST-1 and lack of exotoxin production. We also suggest that apurulence in an S. aureus-infected burn wound in a child should not be used to rule out toxic shock syndrome.