In vivo mapping of a protective linear neutralizing epitope at the N-terminus of alpha hemolysin from Staphylococcus aureus.

Staphylococcus aureus is responsible for a large and diverse burden of human disease associated with significant morbidity and mortality. The dynamic challenge of this pathogen is exemplified by the emergence of highly virulent community-associated methicillin-resistant S. aureus strain USA300, which threatens both healthy and vulnerable individuals and constitutes a public health imperative in the United States. Though S. aureus employs many virulence factors that enable infectivity and evasion of host defenses, evidence suggests that the increased production of alpha hemolysin may be a critical contributor to the increased virulence of USA300. To enable and inform immunological targeting of alpha hemolysin, we sought to precisely map a neutralizing epitope that we hypothesized existed in the N-terminal domain. Using an in vivo mapping strategy employing peptide immunogens and an optimized in vitro toxin neutralization assay, we identified a linear neutralizing determinant in the N-terminal 19 amino acids of alpha hemolysin. Affinity purified rabbit antibody against this neutralizing epitope was shown to be highly effective at mitigating dermonecrosis in inbred and outbred mice challenged with USA300. To our knowledge, this is the first description of a linear neutralizing epitope in alpha hemolysin, and the delineation of this determinant should inform and facilitate the rational design and development of an efficacious, epitope-focused or multivalent vaccine against S. aureus.