Evaluation of Genetically Inactivated Alpha Toxin for Protection in Multiple Mouse Models of Staphylococcus aureus Infection

Abstract

Staphylococcus aureus is a major human pathogen and a leading cause of nosocomial and community-acquired infections. Development of a vaccine against this pathogen is an important goal. While S. aureus protective antigens have been identified in the literature, the majority have only been tested in a single animal model of disease. We wished to evaluate the ability of one S. aureus vaccine antigen to protect in multiple mouse models, thus assessing whether protection in one model translates to protection in other models encompassing the full breadth of infections the pathogen can cause. We chose to focus on genetically inactivated alpha toxin mutant HlaH35L. We evaluated the protection afforded by this antigen in three models of infection using the same vaccine dose, regimen, route of immunization, adjuvant, and challenge strain. When mice were immunized with HlaH35L and challenged via a skin and soft tissue infection model, HlaH35L immunization led to a less severe infection and decreased S. aureus levels at the challenge site when compared to controls. Challenge of HlaH35L-immunized mice using a systemic infection model resulted in a limited, but statistically significant decrease in bacterial colonization as compared to that observed with control mice. In contrast, in a prosthetic implant model of chronic biofilm infection, there was no significant difference in bacterial levels when compared to controls. These results demonstrate that vaccines may confer protection against one form of S. aureus disease without conferring protection against other disease presentations and thus underscore a significant challenge in S. aureus vaccine development.

Role of Antibodies in Protection Elicited by Active Vaccination with Genetically Inactivated Alpha Hemolysin in a Mouse Model of Staphylococcus aureus Skin and Soft Tissue Infections

“…The effect of vaccination on the protection of Jh mice compared to the protection of wildtype BALB/c mice was then assessed. As was observed previously (20), at 14 days postchallenge, BALB/c mice immunized with adjuvanted HlaH35L had significantly less bacterial colonization ( Fig. 2A) and visibly less tissue damage of the affected ear (Fig.…”

“…Alternatively, because secreted toxins cause localized tissue damage, the neutralization of alpha hemolysin may decrease subsequent nutrient release from host tissues and lessen the ability of S. aureus to further invade the host. This idea is supported by decreased levels of tissue destruction in HlaH35L-immunized mice (20). Whatever the mechanism, active toxin appears to be involved in the survival of the bacteria (23), and anti-Hla antibodies clearly play a pivotal role in the protection afforded by active immunization with an inactivated Hla-based vaccine in this SSTI model.…”

“…The concentration was verified by serial dilution and plating on TSA. The mice were anesthetized and challenged as previously described by Brady et al (20). Seven days postchallenge, each mouse was euthanized, and its affected ears were imaged when indicated.…”

“…Enzyme-linked immunosorbent assays (ELISAs) to measure mouse antibodies were performed as described by Brady et al (20). ELISAs to measure rabbit antibodies were performed according to the same protocol; however, the conjugate antibody used was goat anti-rabbit IgG conjugated to horseradish peroxidase (HRP) (Bio-Rad Laboratories, Hercules, CA).…”

Evaluation of Antibiotics Active against Methicillin-Resistant Staphylococcus aureus Based on Activity in an Established Biofilm

“…taphylococcus aureus is a leading cause of both hospital and community-acquired infections (1). S. aureus causes many different types of infections, but among the most common are infections associated with indwelling medical devices (2,3).…”