Evaluation of Approaches to Monitor Staphylococcus aureus Virulence Factor Expression during Human Disease

Abstract

Staphylococcus aureus is a versatile pathogen of medical significance, using multiple virulence factors to cause disease. A prophylactic S. aureus 4-antigen (SA4Ag) vaccine comprising capsular polysaccharide (types 5 and 8) conjugates, clumping factor A (ClfA) and manganese transporter C (MntC) is under development. This study was designed to characterize S. aureus isolates recovered from infected patients and also to investigate approaches for examining expression of S. aureus vaccine candidates and the host response during human infection. Confirmation of antigen expression in different disease states is important to support the inclusion of these antigens in a prophylactic vaccine. Hospitalized patients with diagnosed S. aureus wound (27) or bloodstream (24) infections were enrolled. Invasive and nasal carriage S. aureus isolates were recovered and characterized for genotypic diversity. S. aureus antigen expression was evaluated directly by real-time, quantitative, reverse-transcriptase PCR (qRT-PCR) analysis and indirectly by serology using a competitive Luminex immunoassay. Study isolates were genotypically diverse and all had the genes encoding the antigens present in the SA4Ag vaccine. S. aureus nasal carriage was detected in 55% of patients, and in those subjects 64% of the carriage isolates matched the invasive strain. In swab samples with detectable S. aureus triosephosphate isomerase housekeeping gene expression, RNA transcripts encoding the S. aureus virulence factors ClfA, MntC, and capsule polysaccharide were detected by qRT-PCR. Antigen expression was indirectly confirmed by increases in antibody titer during the course of infection from acute to convalescent phase. Demonstration of bacterial transcript expression together with immunological response to the SA4Ag antigens in a clinically relevant patient population provides support for inclusion of these antigens in a prophylactic vaccine.

S. aureus colonization in healthy Australian adults receiving an investigational S. aureus 3-antigen vaccine

“…Immunogenicity was assessed using a triplex competitive Luminex R immunoassay (cLIA) which measures competition between serum immunoglobulins and antigen-specific monoclonal antibodies for binding to the respective antigen-coated microspheres. 45…”

Safety, tolerability, and immunogenicity of a novel 4-antigen Staphylococcus aureus vaccine (SA4Ag) in healthy Japanese adults

“…Immune responses were measured by immunoassays that monitor functional responses to each antigen: the OPA assay 12,14 for CP5 and CP8; the FBI assay 12,24 for ClfA; and the cLIA 17,25 for ClfA and MntC. These assays were performed on blood samples collected during each study visit.…”

The complex biology and contribution ofStaphylococcus aureusin atopic dermatitis, current and future therapies

“…Such approaches could neutralize virulence determinants and also target the bacteria for opsonophagocytic killing by immune cells. SA4ag and 4C‐Staph are two vaccines comprised of multiple antigens: SA4ag consists solely of S. aureus surface antigens whereas 4C‐Staph includes surface antigens and α‐toxin . These vaccines look encouraging in some preclinical models but there are no reports of them having activity in S. aureus skin infections and they have yet to be tested in preclinical models of AD.…”